What If the Universal Gravitational Constant Changed?

[jackster18]

If the universal gravitational constant was changed from 6.67 X 10^-11 to 6.67 X 10^+11 what would happen?
Hi. I am doing a physics project for grade 12 physics. Here is the question: The universal gravitational constant, G, is suddenly changed from 6.67 X 10^-11 Nm^2/kg^2 to 6.67 X 10^+11 Nm^2/kg^2. Discuss the implication of such a change.
- What changes would there be in your life? The life of your descendants?
- In what ways would life be different? What safety precautions would you have to exercise?
- Think about everyday life and how it would be changed in such an environment.
- You have all the money and resources that you need. How are you going to redesign the world to accommodate this change?

So far i have calculated that if this did occur, FG would be 1.0 X 10^22 times stronger than what it would normally be on earth. So basically everything would just be crunched into a ball. Actually everything in the universe would just get smashed together into a huge ball. If you can help try and answer some of the question above, thanks. It’s worth 12% of my mark :(.

My teacher gave me a hint and told me to calculate how long it would take for the Earth to crash into the sun and compare that to how long it would take for Pluto to do the same.

This is the way it is being marked is:

Creativity #/10
-originality
-entertainment value
-insight

Sensory Impact #/10
-neat
-quality
-time/effort

Physics Implications #/10
-references to kinetics and dynamics
-mathematical calculations
-insight

Presentation:
Multimedia
-report
-comic
-magazine
-newspaper
-text/photos
-slide show
-oral presentation
-dramatic presentation
-video
-power point
-poster
-etc...
So we can basically present it any way we want my teacher said.

Must be neat/professional/signs of time and effort/eye catching/holds attention

Physics Content:
-Reference to laws (Newton’s 3 laws)
-how changes affect our lives
-calculations to quantify the effects
-demonstrates a clear understanding of Universal Law of Gravity

So as I said, if anyone can help I would greatly appreciate it because this project is worth 12% of my mark.

 

[rbj]

okay, Jackster, this might be difficult to get, and i wouldn't have understood it when i was in high school (which was 34 years ago), but, it turns out that it is actually a meaningless question about what operationally changes if some dimensionful parameter or "constant" changes. when we measure a physical quantity, we do so against a like-dimensioned standard (often this is called a "unit") and that ratio of like-dimensioned quantities, a dimensionless number, is the salient quantity that we measure or simply perceive in our everyday experience. (e.g. when we measure a length of something, we are actually counting tick marks on a ruler or tape-measure. similarly, when we measure a period of time, we are counting ticks of some kinda clock.)

if you go to the relativity forum, you will see similar questions about why the speed of light, c, is what it is and the same issues regarding measurement and perception apply. whether it is G or Planck's constant h or c, all of these quantities can be set to the constant 1, if you define everything in terms of Planck Units. i would recommend to check out the Wikipedia article regarding Planck units, but recently some editors have really f\mucked it up. so if you go to that article, hit the "history" tab and view a version that is a couple months old, and you will have a better read.

the thing is that Nature doesn't give a rat's ass what units we humans (or the aliens on the planet Zog) choose to use. if we choose to measure things in terms of Planck units, there is no graviational constant, no Planck's constant, no speed of light to change. they are all normalized to 1.

now, if you think that you measured a change in any of these dimensionful parameters (given some anthropocentric units like meters, kilograms, and seconds), what really changed was the number of Planck Lengths per meter or the number of Planck Times per second or the number of Planck Masses per kilogram. those numbers are dimensionless and asking why those numbers are what they are is the meaningful question. but if you measure and define everything in terms of Planck units, there simply is no G, c, or \hbar to vary, they are removed from all mathematical expressions of physical law.

 

[Loren Booda]

jackster18,

If gravitational force were increased by 22 powers of ten, it might not affect the other fundamental forces (strong, weak, electromagnetic - still a factor of 10¹⁵ removed) directly, but it most likely would affect the size of masses and most certainly their orbits.

In addition to changes in the Planck units (like the Planck mass), cosmological parameters including the horizon radii of the universe and black holes would probably reduce 10²² times. Look out also for effects of gravity that could rely on its strength squared, maybe feeding back into such calculations.

Remember that homework belongs in another forum.

 

[mikelepore]

- What changes would there be in your life? The life of your descendants?
- In what ways would life be different? What safety precautions would you have to exercise?
- Think about everyday life and how it would be changed in such an environment.
- You have all the money and resources that you need. How are you going to redesign the world to accommodate this change?

Aren't these funny question to ask about a change that would utterly destroy the whole reality that we know? Similar in anticlimactic characteristic to asking someone: Suppose our entire universe were suddenly annihilated -- how would you reorder your personal priorities for the rest of the afternoon? Everything everywhere is going to be obliterated tomorrow: have you prepared yourself by stocking up on flashlight batteries and bottled drinking water? This sounds like a psychology experiment about how the phrasing of a question can alter the boundaries in which people conceive of an answer.

 

[ks_physicist]

Hmm. Calculate your Schwarzschild radius, that of your car, your house, Sol, etc. with each value.

 

[rbj]

jackster18,

If gravitational force were increased by 22 powers of ten, it might not affect the other fundamental forces (strong, weak, electromagnetic - still a factor of 10¹⁵ removed) directly, but it most likely would affect the size of masses and most certainly their orbits.

In addition to changes in the Planck units (like the Planck mass), cosmological parameters including the horizon radii of the universe and black holes would probably reduce 10²² times. Look out also for effects of gravity that could rely on its strength squared, maybe feeding back into such calculations.

Remember that homework belongs in another forum.

Hmm. Calculate your Schwarzschild radius, that of your car, your house, Sol, etc. with each value.

okay guys, the issue is what would happen if G changed its value with no reference to a change in any of the 26 or so dimensionless fundamental universal constants. there's a reason that neither G nor c nor \hbar are on that list of 26. if all of the dimensionless constants remained constant, you could not know if there was a change in one of these dimensionful constants in and of itself. if, say, the ratio of the Bohr radius (about the size of atoms) to the Planck Length remains constant, if the ratio of the elementary charge to the Planck Charge, if the ratio of the period of Cesium radiation (that they base the second on) to the Planck Time were constant, if the ratio of the particle masses to the Planck Mass remained constant, if none of those change, a change in G is meaningless. everything else would adjust in such a way so that when we measure G, it would, in terms of "new" meter sticks, kilogram standards, and cesium clocks, come out to be the same, from our ability to measure it.

okay, if you say "a change in G means that one (or more) of those ratios changed", then i would say that the root issue is that that dimensionless ratio (or ratios) changed. it's the dimensionless parameters that are the salient parameters. the Wikipedia Planck units article at least used to quote from a book by John Barrow about the Constants of Nature. i'll try to find it and quote it here.

 

[rbj]

that quote from Barrow is regarding the same question except it's c that's changing. but the same principle regarding dimensionful vs. dimensionless varying "constant" applies.

[An] important lesson we learn from the way that pure numbers like α define the world is what it really means for worlds to be different. The pure number we call the fine structure constant and denote by α is a combination of the electron charge, e, the speed of light, c, and Planck's constant, h. At first we might be tempted to think that a world in which the speed of light was slower would be a different world. But this would be a mistake. If c, h, and e were all changed so that the values they have in metric (or any other) units were different when we looked them up in our tables of physical constants, but the value of α remained the same, this new world would be observationally indistinguishable from our world. The only thing that counts in the definition of worlds are the values of the dimensionless constants of Nature. If all masses were doubled in value [including the Planck mass m_P] you cannot tell because all the pure numbers defined by the ratios of any pair of masses are unchanged.

John Barrow, 2002, The Constants of Nature

 

[Loren Booda]

What matters is that the change in G is relative (in the sense of measurement units, not necessarily velocity or acceleration dependence) to the observer. Therefore, whatever is an object to this observer would embody the change in G. Dimensionless fundamental "constants" are no more fundamental or constant than the established G with respect to the observer.

 

[rbj]

What matters is that the change in G is relative (in the sense of measurement units.

okay, so today you measure the length of some thing to be 10.01 cm in length using some ruler and tomorrow you measure the same thing (with the same ruler) to be 10.03 cm. do you know that it was that thing that changed or if it was your ruler that changed? or maybe a little of both? all you really know is that ratio of lengths changed. that is fundamentally all you know.

Therefore, whatever is an object to this observer would embody the change in G.

dunno what that means.

Dimensionless fundamental "constants" are no more fundamental or constant than the established G with respect to the observer.

that, i completely disagree with. and i think that physicists like Barrow, Baez, and Duff would also disagree with it.

 

[Loren Booda]

To be observed as true constants, dimensionless fundamental constants require simultaneity for demarcation and comparison of at least two spacetime points. Objectivity requires the thing and the ruler likely nonsimultaneous (nonidentical), i. e., compared between at least two (probably four) events. For measurement, the ruler requires 2 points in space, the thing 2 points in space, and the lapse of time 2 points each for ruler and thing.

The result is that dimensionless parameters may be constant or not, but to a participating observer, most likely not (vanishingly simultaneous). One does not know whether the laboratory standard (ruler) is perfectly objective in comparison to the quantum mechanics of measurement. Also, when we observe the value of either a dimensional or dimensionless parameter, we are comparing it to an internalized standard of the same dimension - a third improbability of inconstancy.

 

[jackster18]

Thanks everyone for trying to help, i do appreciate it, but I have no clue what anyone is talking about. I am only in grade 12, i think i know less then 5% of what you guys are saying. If possible please put it in lame mans terms :/ .

 

[jackster18]

Also some of the words everyone is using makes my mind spin. I guess my vocabulary is low :(.

 

[Loren Booda]

The Newtonian constant G affects the strength of gravitational attraction. It determines the orbit of planets, the weight and acceleration of massive objects, (at least in part) the birth and death of the universe, and the bending of spacetime - most prominently near black holes. If you increase the value of G by 10²², it will increase all of these forces likewise.

 

[rbj]

Thanks everyone for trying to help, i do appreciate it, but I have no clue what anyone is talking about. I am only in grade 12, i think i know less then 5% of what you guys are saying. If possible please put it in lame mans terms :/ .

Also some of the words everyone is using makes my mind spin. I guess my vocabulary is low :(.

i'm trying not to use big words or anything like that. i just want you to consider the thought: what if you today measured some thing, say the height of your favorite beer mug, to be 15 cm tall, and tomorrow you took the very same ruler and measured the very same beer mug and found it to be 16 cm tall. what changed? was it the beer mug or was it the ruler (or maybe a little of both)? whatever it was, the net thing you did is measure a dimensionless quantity by counting the tick marks on the ruler. that is the way it is with any physical experiment, any physical measurement. we only measure dimensionless values. we only perceive the mass or size or time of stuff in relative terms. if some dimensionless constant changes (like the ratio of proton mass to electron mass, which is about 1836 something) then we know the difference. if it's just a single dimensionful quantity that is alleged to have changed, we would not know the difference. nothing would be different, including what we think the value of that dimensionful quantity is.

The Newtonian constant G affects the strength of gravitational attraction. It determines the orbit of planets, the weight and acceleration of massive objects, (at least in part) the birth and death of the universe, and the bending of spacetime - most prominently near black holes. If you increase the value of G by 10²², it will increase all of these forces likewise.

Loren, the Newtonian constant, G, is something that we measure with our meter sticks, clocks, and kilogram standards. it does not represent a parameter of the universe that Nature defines or even knows about. like the speed of propagation of the fundamental interactions (E&M, gravity, nuclear forces), what we denote as c, nature does not define a particular quantitative value for it, except that it is real, positive, and finite. that's it. Nature does not decree it to be 6 x 10^-11 anything. that value is a construct purely of human origin that had its birth when Cavendish constructed the first experiment to measure this gravitational interaction using meters, kilograms, and seconds (maybe he used English units, i dunno).

you should take a good look at the Wikipedia articles on Planck Units and Fundamental Physical Constants. but look at a version of Planck Units before March 2008 like this one, because some new editors have screwed the article up, and i am no longer trying to defend it from BS. please read the section entitled Planck units and the invariant scaling of nature (where i got that Barrow quote). the example there was about the meaning of a changing c, but it could be the meaning of a changing G and the principle would be the same. if any single dimensionful constant changed, yet all of the dimensionless constants (all of the dimensionless ratios of like-dimensioned physical quantity) remained the same, no mortal would notice any difference. if G suddenly increased by a factor of 10²², then the Planck length would be (from God's POV, not ours) 10¹¹ times longer. but since the axiom is that the dimensionless constants remain the same, so would the meter be 10¹¹ longer, we would 10¹¹ times taller and fatter (from "God's POV" or whatever observer who is unaffected by physical law) but we wouldn't know the difference. the size of and distance between planets would increase (from "God's POV") by the same factor. but relative to us and our meter sticks, they would appear to be just the same size as before. the Planck Mass would be reduced by factor of 10^-11 and so would the masses of atoms, people, planets, and the big steel balls in the Cavendish experiment. clocks would tick slower by the same factor, including the period of Cesium radiation we use as a time standard. but so would our minds and our sense of time. when we run the Cavendish experiment to again measure G, it would, from our mortal perspective, come out to be the same number as it had before.

if we measure any changing in G (conceivably a change in measurement is conceptually possible), the net quantities measured (that we determine G from, in terms of our meters and kilograms and seconds) are all dimensionless numbers. it is those dimensionless numbers that are salient. G is just a human construct. an artifact of the units we arbitrarily established to measure things and Nature doesn't give a rat's ass what units we use to measure things.edit: here is a reference to that article by Michael Duff: Comment on time-variation of fundamental constants where he takes on specifically claims of a varying c, but applies the same reasoning to G.

 

[jackster18]

I understand what your traying to say. That you could measure in any units you wanted. Like my name is Jack. I could say...1 m = 2.35 Jack's. But your trying to say that if G did change everything else would change along with it?

What I am trying to say is that if just G itself changed, along with nothing else changeing what would happen, if you were even able to watch it happen.

And yes, i understand what you mean about the ruler, that you don't really know what changed...so like, if G did change ur saying that we wouldn't really know if G changed. It may have been something else that changed, or something else changed along with G chaninging at the same time? And this is because if G changed, other things would change along with it...as in us getting fatter you said, so really we would see no change at all. I think i get what you mean.

I will try and find that article your talking about.

 

[jackster18]

On the link you had set up i found this by clicking (V1) at the bottom:

The possible time variation of dimensionless fundamental constants of nature, such as the fine structure constant alpha, is a legitimate subject of physical enquiry. By contrast, the time variation of dimensional constants, such as h-bar, c, G, e, k..., which are merely human constructs whose number and values differ from one choice of units to the next, has no operational meaning. To illustrate this, we refute a recent claim that black holes can discriminate between two contending theories of varying alpha, one with varying c and the other with varying e.

But how do i get the rest of the article?

 

[jackster18]

What my teacher is basically asking for is what would happen if the force of gravity is increased. Meaning if just the force of gravtiy increased and everything else stayed the same.

 

[Dale]

rbj's point is maybe a little advanced for high-school level physics, but perhaps it might help to learn a little about http://en.wikipedia.org/wiki/Planck_units" . In Planck Units all of the fundamental constants like G, c, and h are set to 1. Although the resulting units would be a little difficult to use in everyday situations they represent a more fundamental system of units than SI.

Usually when textbooks talk about G they talk about how small it is. They compare it with the Coulomb constant which is relatively large and talk about gravity being a weak force. However, in Planck units the question is a little different. In Planck units gravity and electrostatic attraction are the same "strength", and what is different is that the mass of a proton is much smaller than its charge.

So, instead of asking "why is gravity so weak and what would happen if it were stronger?" you could ask "why are the masses of elementary particles so small and what would happen if they were greater?" The answer will be what your teacher is actually looking for, but with more insight into the nature of unit systems and universal constants.

 

[Loren Booda]

Thank you rbj and DaleSpam for persevering and elucidating why units like those of the Planck system can be arbitrarily fixed, most commonly to 1. I still entertain whether the observer, through the relativity or uncertainty of its measurements, can disturb the objectivity of such a system. Just a thought.

 

[rbj]

But how do i get the rest of the article?

hit the PDF link in the upper right.

Dale, you're right about the level of this, and i tried to warn Jackster about that. I just didn't want him doing this paper for HS and saying stuff like that Mr. Tompkins story.

jackster, to be clear, if just G changed to another real, finite, and positive value and none of the dimensionless fundamental constants that Baez listed changed, you and every other mortal (who, along with your tools and instruments, must be subject to the same physical laws that have G in them) can not know the difference. if the number of Planck Lengths per meter remain constant, and the number of Planck Times per second remain constant, and the number of Planck Masses per kilogram remain constant, then when we set about to measure G again, we'll measure it to be the very same value.

now, if we somehow measure it to be a different value, and we notice it and say to each other "G appears to have changed its value to [whatever]", then what happened is either one, two, or all three of these things changed: the number of Planck Lengths per meter changed, or the number of Planck Times per second has changed, or the number of Planck Masses per kilogram has changed. being ratios of like-dimensioned stuff, those are dimensionless numbers and if they change, it's salient and we'll know it.

 

[ks_physicist]

RBJ, when I have time I am going to read the references you mention in more depth.

Still, in this case, it is clear that the teacher wants to know what would happen if when you calculated the gravitational force using F=Gmm/r^2, you used a different numerical value of G.

 

[rbj]

RBJ, when I have time I am going to read the references you mention in more depth.

Still, in this case, it is clear that the teacher wants to know what would happen if when you calculated the gravitational force using F=GMm/r^2, you used a different numerical value of G.

well, if the M and m and r are the same, then F will come out different.

but if the question is what if G changes and only G changes, then my response is that all by itself, it's an "operationally meaningless" question. such a difference is "observationally indistiguishable". (quotes from Duff and Barrow.)

or another way to say it is if we measure everything in terms of Planck Units (and we are allowed to do that, Nature doesn't care what units we use), there simply is no G to vary, no c to vary, no h to vary.

 

[jackster18]

Originally Posted by RBJ
"but if the question is what if G changes and only G changes, then my response is that all by itself, it's an "operationally meaningless" question. such a difference is "observationally indistiguishable". (quotes from Duff and Barrow.)"

This is what the teacher wants. And to my teacher it is operationally meaningful...i guess.

originally posted by RBJ
"or another way to say it is if we measure everything in terms of Planck Units (and we are allowed to do that, Nature doesn't care what units we use), there simply is no G to vary, no c to vary, no h to vary."

This plank units thing was also posted by other people as well. Yes i do appreciate everyone trying to help but my teacher does not want anything to do with Plank Units. We don't learn that in grade 12 and i asked him about it and he said not to put stuff like that in it.
__________________

 

[rbj]

well, i can't help you about your teacher. your teacher has company with some physicists who have proposed the possibility of such dimensionful universal "constants" changing. but, from what i can tell from here at PF, at the sci.physics.research newsgroup, from blogs and webpages of various active leading physicists and from their publications, the constants of Nature that are salient are only the dimensionless constants. probably the two most commonly referred to are the Fine-structure constant and the Proton/electron mass ratio.

whether they are called "planck units" or "foos and fargs", you should be able to tell your teacher and your class (if you're presenting this) that you can always choose units that can make G be whatever finite and positive value you want (so why not one).

here is a little more of this. for every measurement system, there are Base Units and there are Derived Units. most often the base units include the units of length, time, and mass. ("length", "time", and "mass" are dimensions of physical quantity, no matter what units one might use to measure such. you can add, subtract, compare and equate physical quantities only if they have the same dimension. it is not meaningful to add one meter to one kilogram. but with appropriate conversion factors you can meaningfully add 1 meter to 1 inch.)

now in the SI system of units, these base units (meter, kilogram, second) were determined completely independently and anthropocentrically. that's history. then we came up with derived units for quantities like velocity (meters per second), acceleration (meters per second per second), force, and energy. now let's take a look at the last two:

we know that Force is proportional to the rate of change of momentum or, if the mass is constant, proportional to mass times acceleration. we would write this as:

F \propto m a

or

F = K \ m a

where K is our constant of proportionality. now, i could define a unit of force i'll call a Farg. and i'll define a Farg so that 1 Farg of force will accelerate 2 kilograms by 1 m/s². without units in the equation that would look like

F = \frac{1}{2} \ m a

m=2, a=1, and we would be left with F=1. that constant of proportionality is not just 1/2, it is "1/2 Farg-second² per kilogram-meter". now you and/or your teacher might suggest that is just stupid. why choose a unit of force so that you have to remember that conversion factor in the equation for Newton's 2^nd law? so, instead, smarter people than me choose a unit of force that they called a "Newton" such that 1 Newton of force will accelerate 1 kilogram by 1 m/s². now then you would still have

F = K \ m a

but now K would be a conversion factor that is "1 Newton-second² per kilogram-meter". if you considered force to be dimensionally a completely different quantity than mass times acceleration, you would need that conversion factor in there just to convert quantities of dimension "mass times acceleration" into a quantity of dimension "force". but if instead we say that "force is precisely the same quantity as mass times acceleration", then we don't need that K at all. we can say

F \ = \ m a

and understand that a Newton is not just proportional to a kilogram-meter per second², that it is a kilogram-meter per second². that's what a Newton means. it was deliberately defined to be none other than a kilogram-meter per second² so that we can say F=ma and completely get rid of the constant of proportionality. This is what is meant by the unit of force, the "Newton", is a "derived unit", not a base unit.

That's also what they did to define a unit of energy, the Joule. energy (or "work") is not just proportional to force times distance, we will define it to be the same as force times distance. from that we get that a Joule is a Newton-meter or a kilogram-meter² per second². Again, the unit of energy here in SI, is a derived unit, not a base unit.

Now, here is where your teacher has to pay attention: we defined the meter, kilogram, and second completely arbitrarily (or anthropocentrically). that is we, from the POV of Nature, pulled these unit definitions from out of our butt. but they are there; we have a unit of length, a unit of mass, and a unit of time. Then using those units (that we pulled out of our butts) we set out to measure some physical phenomena, some which appears to us to be universal, particularly the speed of light c, the gravitational constant G, and Planck's constant \hbar. Given those base units we started with, those 3 quantities are measured to be numbers. We can write them down. But that is because those unit definitions were fixed, predetermined with no prior consideration of the speed of light c, the gravitational constant G, and Planck's constant \hbar.

But suppose, instead, we think like we were thinking above in how we defined the derived unit of force and unit of energy. What if we held off and said, "Let's not define our units of length, mass, and time just quite yet. Let's play around with their definitions" - we have 3 degrees of freedom to fiddle with, until we get definitions of length, mass, and time so that in the physical equations that use c, G, and \hbar, those numbers come out to be 1 in terms of these units. Are we not allowed to do that? Would nature care? Does Nature give a rat's ass what units we use to measure stuff?

If we do that "there simply is no G to vary, no c to vary, no h to vary" but there is somethings that could change that we (or Nature) would care about. The meter is about as tall as we are (within an order of magnitude). If the number of Planck Lengths (that's the unit of length we just defined above) per meter changed, then sometime substantive changed. Life would be different. It's "observationally distinguishable" or "operationally meaningful". But the number of Planck Lengths per meter is a dimensionless number. If your meter stick is a "good" meter stick, it should not be losing or gaining atoms. If the number of Planck Lengths per meter (stick) changed, that means the number of Planck Lengths in the size of an atom (somewhere around what is called the Bohr radius) has changed.

So that is one place where such a meaningful question could be posed to the physicists: "What would happen if the number of Planck Lengths per Bohr radius changed? How would life be different?" You could do the same with time: "What would happen if the number of Planck Times changed in a period of Cesium radiation (that they base the second on)? How would that change things?" And you can ask such about mass: "What would happen if the amount mass of atomic particles (in terms of the Planck Mass) has changed measurably? How would that change things?" Asking those questions are meaningful because they are asking about dimensionless numbers that would be the same no matter what system of units are used. If we thought that we measured a change in G or c, it's really because one or more of those dimensionless ratios changed, and that is the salient question to think about.

If this cannot be at least mentioned in your assignment, if your teacher won't allow that, then he/she is being ignorant and you should send him/her over here and we'll straighten him/her out.

 

[Dale]

This plank units thing was also posted by other people as well. Yes i do appreciate everyone trying to help but my teacher does not want anything to do with Plank Units. We don't learn that in grade 12 and i asked him about it and he said not to put stuff like that in it.

That is pretty sad. That kind of thing really discourages intellectual curiosity. My recommendation is not to fight it. If he specifically said to not do it rigorously then there is nothing left for you but to prepare a boring analysis.

I would focus on the http://en.wikipedia.org/wiki/Schwarzschild_radius" in my paper. Basically, with such a huge change in G you should find that the Earth turns into a black hole. So much for decendants. It would have been a much more interesting paper if he had changed it by a factor of 2 instead of ~10^22.

 

[jackster18]

Originally Posted by dalespam
"It would have been a much more interesting paper if he had changed it by a factor of 2 instead of ~10^22."

Yea there was a list of about 7 or 8 questions one of them was if Fg was halved and another was if Fg was doubled...those two were the ones i understood most but other groups picked them b4 i got to pick so my group got left with this dumb question. Luckaly i have a group member who gets like 95% in every class, he got a 98% in calculus and 97% in advanced fuctions and got 95 in physics last year (grade 11) so i hope he will be able to figure it out.

 

[Dale]

Well, about all that I can think of doing with this paper is saying that the Earth turns into a black hole. You can spend a while describing what a black hole is and what an event horizon is. Then you can spend the rest of the paper describing in agonizing detail the theoretical experience of falling into a black hole. You can cite http://arxiv.org/PS_cache/arxiv/pdf/0705/0705.1029v1.pdf" about maximizing the survival time beyond the event horizon. You should probably be able to find some screen-shots of what the view would be like as you cross the event horizon.

Basically turn it into a report about black holes since that is all that you would have after such a huge change.

 

[jackster18]

yea i was planning on talking about black holes

 

[robertm]

It sounds to me as if your teacher hasn't even begun to understand the concepts behind the questions he/she asks. I am also a senior in hs and have many times over heard the "thats not what I am looking for" or "we arent covering that matterial" . It took me about half a day to understand the implications of this question that rbj and others where trying to point out, but just because your teacher inadvertently asked a question with deep implacations doesn't mean you should sell short your own opportunities for knowlege. Include what you have to to make the "grade" (which is also a useless human created unit) and then try and show him the error in his question. I think this is a good opportunity for the student to teach the teacher. Good luck with your project jackster!

 

[Ulysees]

The teacher just wants some demonstration that you know some laws, like how the distance of a planet depends on G for a given period, or how the density of a planet depends on G.

There would be planets, but much smaller in both mass and size.

Stars would be much smaller and denser, emitting light with less mass.

Solar systems would be much larger in extent to be stable.

Galaxies would be much larger in extent to be stable (and not turn into black holes).

In summary: accumulations of normal matter would be smaller, distances between them longer, black holes more massive

 

[rbj]

The teacher just wants some demonstration that you know some laws, like how the distance of a planet depends on G for a given period, or how the density of a planet depends on G.

i think you missed the point.

There would be planets, but much smaller in both mass and size.

Stars would be much smaller and denser, emitting light with less mass.

Solar systems would be much larger in extent to be stable.

Galaxies would be much larger in extent to be stable (and not turn into black holes).

In summary: accumulations of normal matter would be smaller, distances between them longer, black holes more massive

okay, so you are saying that if this dimensionful constant G changes to another value, there would be evidence of some lengths getting smaller while other lengths are getting larger? it would be nice for you to show how that happens (because there is a dimensionless consequence, and such is salient), but take a look at the Duff paper first. because if you lay down some equations that indicate to you that such is the case, i will immediately try to "non-dimensionalize" the equations. if such a consequence happens, likely the cause is a change in the masses of particles relative to the Planck Mass (which is the salient issue).

 

[Ulysees]

okay, so you are saying that if this dimensionful constant G changes to another value, there would be evidence of some lengths getting smaller while other lengths are getting larger?

Not exactly. Existing stars and solar systems would accumulate into black holes alright, but interstellar dust would accumulate into small stars and small planets rotating around them, at a very long distance.

A planet with the Earth's diameter would probably have 10^22 times less mass and rotate 10^22 times further from its sun (centripetal acceleration = r*w^2). Or something like that, cause density is not constant inside planets and stars, the maths is probably too hard to do analytically.

Now I don't know how you got distracted into thoughts about constant dimensions. I think the teacher didn't say

"let's change our units of G and see what happens",

but he said

"let's imagine gravity begins to get stronger, as if by magic".

 

[Ulysees]

By the way, there are arguments from religious people that all universe constants are such as to make life possible. I don't know how they came up with this, but it may be that the teacher was inspired from those arguments.

Anyone heard of Hawking saying something like "the universe is such that it supports the existence of the observer, the observer makes it such that the observer exists", or something in that line?

I was trying to trace this saying by Hawking, how exactly it was phrased, and the implications, but haven't found it yet.

 

[rbj]

Not exactly. Existing stars and solar systems would accumulate into black holes alright, but interstellar dust would accumulate into small stars and small planets rotating around them, at a very long distance.

then you're saying that ratios of like-dimensioned quantity changed. that's what happens if some lengths increase and other lengths decrease. even if both lengths are a statistical measure. that would be an "observational distiguishable" or "operationally meaningful" consequence. so you're saying that if none of the 26 or so dimensionless universal constants of nature (the Baez article that i pointed to and Wikipedia list them) have changed, and if the dimensionful G changed, that some ratio of physical lengths would be measured by humans to have changed. right? that's what you're saying? if that's it, i think it's mistaken.

Now I don't know how you got distracted into thoughts about constant dimensions. I think the teacher didn't say

"let's change our units of G and see what happens",

but he said

"let's imagine gravity begins to get stronger, as if by magic".

whether by magic or not, doesn't matter. the issue is if G changes and nothing else does, do we know the difference? when you say "gravity begins to get stronger", relative to what is gravity getting stronger? you can't compare directly to another interaction, unless you define an amount of mass (for gravity) and an amount of charge (for E&M) to compare the quantity of interaction. but that's comparing apples to oranges. who decides how much mass to how much charge for the comparison?

if you cite two charged atomic particles (say, for instance, two protons alone in free space), yes, the attractive force of gravity is far, far less than the repulsive force of EM. so the protons fly away from each other like crazy, and that ratio of forces can conceivably be tweaked. but what would really be getting tweeked is either the proton mass to Planck mass ratio (a dimensionless number) or the elementary charge to Planck charge ratio (another dimensionless number) or both. as Wilzcek said, it isn't that gravity is small but that the proton's mass is so small.

By the way, there are arguments from religious people that all universe constants are such as to make life possible. I don't know how they came up with this, but it may be that the teacher was inspired from those arguments.

it's called the Fine-Tuned Universe. and it's an observation that some of those 26 dimensionless fundamental constants of the universe (neither G nor c are among these 26) must lie in a narrow range, otherwise even matter would not exist, let alone life.

it's an observation that deserves an explanation.

Anyone heard of Hawking saying something like "the universe is such that it supports the existence of the observer, the observer makes it such that the observer exists", or something in that line?

I was trying to trace this saying by Hawking, how exactly it was phrased, and the implications, but haven't found it yet.

it's not just Hawking who said so. it's called the Anthropic Principle which is nearly a tautology: "Conditions that are observed in the universe must allow the observer to exist." now, taulogies are generally true, but they are "empty truths" and not so good to build arguments with despite not being false.

by itself the AP does nothing to explain the FTU. combined with a theory of a "multiverse" (there are a few, one comes from string theory or "branes"), the AP and multiverse postulate can be put together to make a coherent explanation of the FTU. i haven't seen nor heard of any proof of the existence of any other universes, and if this one is the only one around, we sure seemed to have been lucky to hit on those constants just right.

 

[Ulysees]

then you're saying that ratios of like-dimensioned quantity changed. that's what happens if some lengths increase and other lengths decrease.

No, it's actually very simple, imagine a computer program (like Celestia) that simulates many objects in the solar system using numerical integration so it can deal with chaotic motion - someone could go to the source code and change a line to another value:

#define G 6.67e-11

Then objects will move differently. That's the idea of the teacher. Same equations, same units, different G. Nothing to do with length expansion or anything relativistic. This is a High School exercise remember.

So can you imagine the effect of changing that constant of the program by 10%? Planets would move faster and in more elliptic orbits closer to the sun. But change the constant by a factor of 10^22, adjust the step of integration to something much smaller for stability, and everything collides with the sun coalescing into a "black hole".

But if you start with an "interstellar cloud" of objects that are much further apart, they'll form a stable solar system of much lighter planets and a much lighter sun, that's all I'm saying. Would life form? Dunno, but if it did, humans would have to be much less dense so they don't get crushed under their own gravity. And that's the sort of answers the teacher is after I think.

 

[Ulysees]

The bit about the anthropic principle is much too interesting and important to discuss it hidden in here, let's make it a thread under Quantum Physics, I think many people including myself will want to understand it.

How they came up with it, what experiments support the underlying concept of the observer giving rise to the existence of the observable and vice versa, all that sort of thing.

 

[Loren Booda]

Quantum Physics? I think the Anthropic Principle is better served by the Philosophy forum.

 

[rbj]

getting a little OT, but not too far OT.

The bit about the anthropic principle is much too interesting and important to discuss it hidden in here, let's make it a thread under Quantum Physics, I think many people including myself will want to understand it.

How they came up with it, what experiments support the underlying concept of the observer giving rise to the existence of the observable and vice versa, all that sort of thing.

Quantum Physics? I think the Anthropic Principle is better served by the Philosophy forum.

yeah, this is more about Cosmology (which all the branches of phyics inform), i would think.

i remember having some discussions about it with a purported physicist at Wikipedia (Userighlander). he added some stuff about it's origin that i thought had both interest and veracity. there were these "Dicke coincidences" that had something to do with the question that wasn't so much "how come do these fundamental constants, that have no known dependence on other parameters, happen to take on these values that allow for matter, solar systems, and planets to form" (the basic FTU question), but Dicke's question was more of "why is the universe about 10¹⁰ years old, instead of 10¹¹ years or 10⁸ years?" and the reason was that, too long and stars (incl. our sun) are going to change and burn out and not be sutitable to sustain life on our planet, too short and these "main sequence" stars would not have happened. i believe there had to be two eras of stars around here, the first bunch of stars were able to cook up elements as far as iron on the periodic chart, but they had to crap out and collapse and there needed to be super novas to cook up the heavier elements for which our planet would have needed 4 1/2 billion years ago.

this is all from memory of reading other sources. i think it reflects what real physicists were saying (and pervect or integral or zap or russ or doc can correct anything they see fit). at least I'm not trying to make anything up. i don't know the details.

anyway, it is a sort of philosophical extension to move the question from "why is the place we're hangin at as old as it is?" to "why are the knobs that manage the place we're hangin at set to the values that they are?" and the Anthropic Principle simply says that, if they were set to much different values (or, for some constants, slightly different values), we wouldn't be here to ask the question. so, it can look like a sort of "well, duh!" explanation but it does have uses (like explaining why the universe isn't a trillion years old).

but the difference is that we know that it had, at one time, been 100 million years old (but there wasn't likely any life around back then asking these questions) and we know (or at least think) that someday the universe will be a trillion years old (and there likely won't be life left around then, but who knows?). so all of these ages of the universe get to have their moment and no age is less likely than any other age, it's just that only some range of ages of the universe that is more likely to be lived in and measured and pondered. the difference is that we don't know that there ever was a universe that had a Fine-Structure Constant that was much different than (137.036)^-1. and if this is the only universe that exists, it is remarkable that these constants took on the values that they had to for matter to be like it is. it then seems we are awful lucky which is the deep question that the notion of the FTU poses.

 

[rbj]

No, it's actually very simple, imagine a computer program (like Celestia) that simulates many objects in the solar system using numerical integration so it can deal with chaotic motion - someone could go to the source code and change a line to another value:

#define G 6.67e-11

but that's a dimensionless number. if you say that everything in Celestia has internal numbers that are fixed to numbers of meters of real things and numbers of kilograms of real thing and numbers of seconds of real intervals of events, changing that dimensionless G would have to change the size of the meters, kilograms, and seconds. that's because, when you write programs to model real physical processes, you have to non-dimensionalize all of the parameters. look up nondimensionalization in Wikipedia. i know from my very own experience in signal processing that we must do that. in modeling audio signal processing, the kernel of the code has no idea that the sampling rate of the physical situation i am modeling is 44.1 kHz or 48 kHz or 96 kHz. it doesn't matter to the program - it just defines the variable parameters (the "states") of the present discrete instant of "time", in terms of the previous discrete instant of "time". all of the parameters must be dimensionless numbers.

Then objects will move differently. That's the idea of the teacher. Same equations, same units, different G. Nothing to do with length expansion or anything relativistic. This is a High School exercise remember.

So can you imagine the effect of changing that constant of the program by 10%?

no, i can't. the whole program can work the same way with G set to 1 (and if you are modeling other physical equations) with c set to 1 and with \hbar set to 1. but now you would be understanding that all of your lengths and masses and elapsed times would be in terms of their Planck units. set the program with the same initial conditions (in terms of these Planck units) and let the program go, and exactly the same thing should happen. and, in fact, exactly that is happening in your modeling program but if G is 6.67 × 10^-11 because somewhere else it is being compensated with the old "multiply and divide by the same quantity trick".

U, you say "it's actually very simple," but remember that "Theories should be as simple as possible, but no simpler." (quote from Einstein.)

Planets would move faster and in more elliptic orbits closer to the sun. But change the constant by a factor of 10^22, adjust the step of integration to something much smaller for stability, and everything collides with the sun coalescing into a "black hole".

ultimately, it's because, in your non-dimensionalized model, the masses of particles in terms of the Planck Mass are getting heavier and/or the size of atoms and constituent particles in terms of the Planck Length are getting smaller and/or the rate of atomic processes (evidenced by the frequency of radiation of particular processes in atoms, such as the Cesium radiation they base the second on) has to be getting faster. those are the salient measures. and somewhere in Celestia or any modeling program, changing G actually changes one or more of those, for something to be observationally different.

just because it's a high school exercise doesn't mean that students should learn fallacies from it.

 

[Ulysees]

#define G 6.67e-11

but that's a dimensionless number.

Of course it's a dimensionless number. It's from a computer program - units are implied.

if you say that everything in Celestia has internal numbers that are fixed to numbers of meters of real things

Or kilometres of real things. Or nanometres of real things. Units are implied in a computer program, and only displayed to the user where the programmer wants to.

changing that dimensionless G would have to change the size of the meters, kilograms, and seconds.

Only if the programmer had to simulate the real world with its given strength of gravity. But this is not about the real world. The teacher's question is about an imaginary, hypothetical world:

"what if the world were different in terms of its gravity strength?"

The teacher might be nice and reward you for the display of off-topic peripheral knowledge, but his question you didn't understand.

the whole program can work the same way with G set to 1

The program would only work the same way if at the same time you changed both G and some other program constant. Eg change all masses by the same factor. But you're not allowed to change anything else: the teacher only asks you to change the gravity strength G.

 

[rbj]

Of course it's a dimensionless number.

but the real G is not. if you're SI, it's 6.67428 × 10^-11 N m² kg^-2 (or, in terms of the base units 6.67428 × 10^-11 m³ kg^-1 s^-2)

It's from a computer program - units are implied.

but their association with the units used to measure real physical quantities cannot be arbitrarily coupled. the "meters" and "seconds" in your simulation are not necessarily the meters of the reality you are simulating. only if G = 6.67428 × 10^-11 m³ kg^-1 s^-2 and c = 299792458 m s^-1 and \hbar = 1.054571628 × 10^-11 kg m² s^-1 will the "meters" and "seconds" and "kilograms" in your simulation represent the real thing in reality. If the simulation is using numbers to represent lengths in meters, time in seconds, and mass in kg, then they can only be associated with the meters, seconds, and kg out here with G, c, and \hbar set to the above values. otherwise the "meters" aren't real meters, they're some measure of length, but what your simulation says is a meter doesn't have anything to do with a meter. unless, of course, the number of Planck Lengths per meter, a dimensionless quantity, has changed (and/or something similar to the second and/or something similar to the kilogram). and that is what is operationally meaningful.

what you don't realize U (and apparently don't wish to realize), is that just increasing G in your simulator probably ended up changing 3 different knobs that are important. it probably made your meter stick (in the simulator) shorter and/or made the masses of all of the particles that make up matter heavier and/or also speed up processes in atoms (which speeds up the processes of things like clocks that are made out of atoms).

Or kilometres of real things. Or nanometres of real things. Units are implied in a computer program, and only displayed to the user where the programmer wants to.

no. they are not of real things. they are scaled. your program will call them "meters" if such display is turned on, but they are shorter or longer than the meters (in reality) that you're associating them with.

Only if the programmer had to simulate the real world with its given strength of gravity.

the whole point is that you cannot meaningfully represent "the strength of gravity" with G. (unless you choose a complete set of natural units, perhaps atomic units, that don't normalize nor define G.) that may seem unintuitive to the high school physics student, but that's the case. the same is true for the Coulomb force constant. do you say that 1/4 \pi \epsilon_0 is what determines the strength of E&M?Ulysees, please read the paper(s) and web pages cited in this thread (but for Planck Units, go back to early March in the history since it's getting screwed up so bad in Wikipedia). read them to the extent that you can reverberate back the concepts and points made therein. maybe buy a copy of John Barrow's book: The Constants of Nature and read at least to page 50. then come back here and make your case with a few equations, because otherwise you're just pissing in the wind.

But you're not allowed to change anything else: the teacher only asks you to change the gravity strength G.

precisely. (at least if you remove the words "gravitational strength" since that meaning is ill defined. but G is well defined.)

and that's why there is no operational meaning to the concept of changing only G. if you're not allowed to change anything else, if you're not allowed to change, say, the (dimensionless) ratio of particle masses to the Planck mass, no one (who is subject to the laws of physics) can know the difference if only G is changed. God (or "Q" on Star Trek or some other omnipotent being that can do such and notice the difference because they, themselves, are not subject to the laws of nature) changes G, and afterward we mortals (who are subject to the laws of nature) set out to measure it with our meter sticks, atomic clocks, and kilogram standards, and with those measuring standards (that are subject to the laws of nature), we find out that it is still appears to us as somewhere around 6.674 × 10^-11 m³ kg^-1 s^-2 . that's the whole point that you need to figure out U.

 

[Ulysees]

It's a shame you don't give a toss about helping that High School student with his teacher's legitimate thought experiment promoting creativity and abstract thought. The teacher is promoting the opposite of what some people here are doing, who like Mr Data endlessly recite sections from books in their "database" unable to think creatively, and often missing the point.

But what is unforgivable is you have continued to flood the thread in an attempt to obfuscate your original misreading of the question with a lot of mostly irrelevant remarks - the teacher was asking for a violation of the laws of physics, in one parameter only. And to only use Newton's laws. That is a legitimate exercise, and the equations accurate as long as speeds are non-relativistic (well below the speed of light).

jackster18, I am sure you are smart enough to give the teacher what he wants, and ignore the flood here. I ensure you, the teacher's underlying models are sound (Newton's laws). And you can use them correctly to calculate what he asks. Unless a final speed works out to be close to the speed of light or over, which it may well do, you can mention this at the end for some extra marks.

 

[rbj]

It's a shame you don't give a toss about helping that High School student with his teacher's legitimate thought experiment promoting creativity and abstract thought. The teacher is promoting the opposite of what some people here are doing, who like Mr Data endlessly recite sections from books in their "database" unable to think creatively, and often missing the point.

But what is unforgivable is you have continued to flood the thread in an attempt to obfuscate your original misreading of the question with a lot of mostly irrelevant remarks - the teacher was asking for a violation of the laws of physics, in one parameter only. And to only use Newton's laws. That is a legitimate exercise, and the equations accurate as long as speeds are non-relativistic (well below the speed of light).

well, since you don't believe me, and since from your usage ("give a toss", "maths") , you sound British. i don't know precisely where it is located, but you might want to consider rolling over to Imperial College and talking to the physics chair, Michael Duff.

physics, indeed all of science, moreover all of learned knowledge, is a continuing revelation of this commodity called "truth". some things we thought were true in times past (like pre-copernicus), we don't think are true today. we've either made discoveries that preclude the older "truth", or we simply thought better of it. (Einstein probably knew about, but never as far as i know, made any reference to the Michaelson-Morley experiment. he just had a better way to think about relative and absolute motion.) it's likely at one time, nearly all physicists thought that the speed of light, as an absolute physical quantity, was a fundamental parameter of the universe. that, if c were somehow changed to 100 km/hour, our experience of reality would be altered. books get written about that like Mr. Tompkins get written with such a view, but now are considered by these leading physicists to be an anacronysm or obsolete. like pre-copernicus astronomy.

the teacher doesn't know it (yet), but was not merely asking about violation of the law of physics. the teacher is asking a sort of meaningless question. it's like looking at a bathtub full of water and asking "what would happen if water were added?" (thinking that the answer is it would measurably overflow.) but when water is added, the tub (and observer and all of the observer's meter sticks) gets bigger and the tub is still full. when water is removed, the tub gets smaller (along with the observer and all of the instruments one would use to measure the volume). the observer cannot tell the difference. and if there is no way for any mortal to know the difference, eventually the question becomes meaningless.

dimensionful parameters, like G, c, and \hbar, are only human constructs. they are not properties of the system associated with them (in this case, the universe). currently, they believe there are about 26 dimensionless parameters that are used in the totality of known physical law. one is the cosmological constant (in terms of the Planck Time) and the remaining 25 come from the Standard Model. the masses of the particles (leptons and quarks) relative to the Planck Mass is as close as you're going to get to a "Strength of Gravity" parameter. if those masses changed (relative to the Planck Mass), something would be different. they may (likely will, IMO) discover new interactions with their own coupling constants that they can only measure and not explain yet with the existing physics. then the number, 26, will increase. they may also discover and verify theories where some of the 26 are derived from other numbers. then the number of fundamental constants will decrease. but the point is that G is not on that list.

obviously, Ulysees, you haven't grasped this point. that's okay.

you say that it's unforgivable that i continue to stand by it, even with regard to jackster, the high school student with an assignment for his physics class. i say what's unforgivable, is for him to have to choose between getting the grade and reporting the accurate physics due to the teacher's ignorance (that's okay, there is plenty of that going around) and arrogance (student may be no more enlightened than teacher under penalty of grade). i had to do similar crap in high school, too, but the issue was about history, sociolgy, economics, and policy. (like writing a paper explaining why capitalism is decidedly better than socialism. or why the U.S. had little choice but to drop the bomb on Hiroshima and Nagasaki. why police act in the best interests of society. why we live in the freest and bestest and happiest of societies and are the envy of nations. why we stand and say the pledge-allegience or sing the national anthem. all that politically correct stuff. when we were little kids, they taught us that George Washington chopped down the cherry tree.)

political orthodoxy is to be expected in a public school, just as you would expect to learn to do the rosary and learn the catechism if you attended a Roman Catholic school. parents who are more enlightened then have to try to help their kids unlearn such brainwashing that cannot be avoided. i just resent (even more) having to do that with science or math (another example: around the turn of the previous century, the state of Indiana nearly passed a law declaring \pi to be 22/7).

 

[ks_physicist]

There is nothing wrong with the question the teacher asked, at the level the teacher asked it. The teacher is not asking students to develop a research proposal for a doctoral thesis, but to think about how G is used and what gravity affects.

Perhaps paired questions would make the intent more clear, such as "Calculate the force of attraction between you and the Earth using the known value of G, and re-calculate it with a value of G equal to 6x10^11."

I can tell you with absolute certainty that I occasionally have to say things to my 9th grade Freshmen that make me feel a little queasy because I'm saying something I know to be "wrong", but I know that I have to present them with the simple version now or they'll be hopelessly lost. When I have them do projectile motion problems, I do not have them factor in the difference in gravitational force due to the altitudes, yet I know that to be "wrong". I teach them kinematics equations, even though they can calculate velocities in excess of c given a constant acceleration and a long enough period of time.

I can imagine the frustration I would see in my students' faces if I spent a class period talking about Planck lengths and dimensionless constants. They're not ready to understand the problem in that depth; it isn't even something that came up as a topic (that I recall) in undergraduate physics. I suspect that you would get the same sort of answer/comment from this student's teacher. (Perhaps the students should invite the teacher to the discussion...)

 

[rbj]

"Calculate the force of attraction between you and the Earth using the known value of G, and re-calculate it with a value of G equal to 6x10^11."

nothing wrong with that. (it's an exercise in math.)

I can imagine the frustration I would see in my students' faces if I spent a class period talking about Planck lengths and dimensionless constants. They're not ready to understand the problem in that depth...

i agree with that and, if you look, i had such a caveat in my first post on this thread.

but, my concern is regarding teaching fallacies to kids (because the truth is a bit more difficult to understand) as fact. that's why Science or NY Times science reporters don't know what questions to ask a physicist who, like the cold-fusion guys, is taking his Variable Speed of Light theory directly to the public media rather than to test it first in the peer-reviewed context. it gets a lot of attention and some excitement, but propagates fallacies. it was precisely such an event that pissed off Michael Duff and prompted him to write that one paper i cited.

 

[jackster18]

good god this is turning into a war

 

[jackster18]

oringinally posted by Ulysees
"But what is unforgivable is you have continued to flood the thread in an attempt to obfuscate your original misreading of the question with a lot of mostly irrelevant remarks - the teacher was asking for a violation of the laws of physics, in one parameter only. And to only use Newton's laws. That is a legitimate exercise, and the equations accurate as long as speeds are non-relativistic (well below the speed of light).

jackster18, I am sure you are smart enough to give the teacher what he wants, and ignore the flood here. I ensure you, the teacher's underlying models are sound (Newton's laws). And you can use them correctly to calculate what he asks. Unless a final speed works out to be close to the speed of light or over, which it may well do, you can mention this at the end for some extra marks."

I don't want to take sides here, but Uly is right rbj...iv been waiting for someone like this to just give me simple answers...its just grade 12, we assume a lot of dumb things when doing calculations..like assume no air resistance...etc. And yea i started skipping what you guys were talking about in your posts because it start to turn into a war of "no I am right, no I am right"...blah blah...lol...Anyways...my group got 29/30, which is 97 % :)...and yea rbj i know its not true physics, like i just said we assume a LOT, and i mean a LOT of stuff...its horrible i know, i guess i will learn REAL physics when i go to university. Heres one of our calculations:

Calculating the time it takes for Earth to reach the Sun with the new universal gravitational constant.

The force of gravity is the only force acting upon the Earth and is therefore the net force. The acceleration towards the Sun can then be calculated. As the Earth gets closer to the Sun (Δd decreases), the force of gravity will increase and so will the acceleration. Assume that the average acceleration of the entire trip, as constant acceleration, accurately represents the changing acceleration of what is actually happening. Also assume that the radius of the Earth and the Sun remain what they currently are (they have not collapsed into themselves with the increased gravity) and use the average distance of the Earth from the Sun. Calculating average acceleration, which will be the average of when Earth is at its current position and when it reaches the surface of the Sun:

Current position:
mE = 5.98x1024 kg
msun = 1.99x1030 kg
Δd = 1.50x1011 m
G = 6.67x1011 N•m2/kg2
Fg = ?

Fg = G * mE * msun / Δd2
Fg = 6.67x1011 N•m2/kg2 * 5.98x1024 kg * 1.99x1030 kg / (1.50x1011 m)2
Fg = 3.53x1044 N

At surface of Sun (where distance between centres is radius of Sun + radius of Earth):
mE = 5.98x1024 kg
msun = 1.99x1030 kg
Δd = 6.38x106 m + 6.96x108 m = 7.0238x108 m
G = 6.67x1011 N•m2/kg2
Fg = ?

Fg = G * mE * msun / Δd2
Fg = 6.67x1011 N•m2/kg2 * 5.98x1024 kg * 1.99x1030 kg / (7.0238x108 m)2
Fg = 1.61x1049 N

Average acceleration:
FNet = (Fg1 + Fg2) / 2
FNet = (3.53x1044 N + 1.61x1049 N) / 2
FNet = 8.05x1048 N

FNet = ma
a = FNet / mE
a = 8.05x1048 N / 5.98x1024 kg
a = 1.35x1024 m/s2



Assuming constant acceleration, the time the Earth takes to reach the Sun from its current position can now be calculated. Also assume that there is only one component to the Earth’s motion, which is towards the Sun, ignoring any of the orbital velocity it had at the beginning (making the initial velocity toward the Sun = 0):
a = 1.35x1024 m/s2
Δd = 1.50x1011 m
v1 = 0
Δt = ?

Δd = v1Δt + ½aΔt2
Δt = sqrt(2Δd / a)
Δt = sqrt(2(1.50x1011 m) / 1.35x1024 m/s2)
Δt = 4.71x10-7 s

Therefore it will take the Earth 4.71x10-7 s to reach the Sun.


And yes i know you see its not real physics but this is what we do in grade 12...its probubly really simple to the people that have been trying to help me here.

But anyways, here's what we wrote:

If the gravitational field were to change from 6.67x10-11 to 6.67x1011, the force of gravity would increase 1.0x1022 times its normal strength. If this occurred all planets and nearby objects (asteroids, comets, etc.) would be pulled towards each other due to the enormous gravitational field between them. Other stars and planets in our solar system would also be pulled towards each other. All of this mass would then be pulled into the black hole at the centre of our galaxy, the Milky Way. Each galaxy in the solar system would do the same thing and eventually the black holes would be pulled towards each other until there was one massive black hole with all of the mass of everything in the universe.

Due to the astronomical increase in the force of gravity, people’s lifestyles would change drastically, not only to survive, but also to continue living a long life. People would have to adapt to a new lifestyle and learn how to cope with a new kind of environment.

If this change did occur we would not be able to adapt in time because we would already be dead. Even if we knew this change was going to take place, we might have some hope of being able to adapt, and possibly find a way to reverse the change. If scientists knew this change was going to occur, they would need to create some sort of invention that would reverse the effects of gravity. If we made no changes all living organisms would die and all nonliving structures such as buildings would collapse in a fraction of a second. Humans would not be able to withstand the enormous force that would immediately crush them. There would be no future generations because all human life would have expired the instant G changed.

One possibility of reversing the effects of gravity would be to build some sort of transparent bubble-like enclosure that could either surround the entire Earth or every object on earth, and stop the change of the gravitational constant. These bubbles would act as a device that could either increase or decrease the gravity of the object. These bubbles could be used in many practical applications.

There would be many safety precautions that we would need to follow in order to keep ourselves alive.

One practical application to take advantage of this ability to change the amount of gravity would be in generating power. An example to generate more power would be in hydroelectric dams. When the water falls over a cliff, it could go through a section where gravity would be increased. When the gravity is increased it would make the water travel at a higher velocity which would increase its kinetic energy which would then generate enormous amounts of electrical energy when passing through the turbine at the bottom of the cliff. This would also mean that the water would only need to fall from short distances in order to create large amounts of energy. This means we could build smaller hydroelectric plants. This could also be applied to wind energy.

The bubbles, which could increase and decrease the force of gravity, could be used in health applications. Many people who are confined to beds or wheelchairs have an increased risk of pressure sores. With nursing help, people who are bed-bound are turned, repositioned and provided with skincare on a regular daily basis. Decreasing gravity would alleviate many pressure sores that these people would otherwise be at risk from.

In addition, these bubbles could be used to do research on humans in zero gravity. These effects could be studied on Earth rather than going out into space. The time and cost needed to study the effects of zero gravity in space would be eliminated.

In jets, there are G forces when the plane turns. If the pilots make too sharp of a turn, then blood rushes down from their head causing them to become unconscious. If there were no G forces there would be no limitations to the maneuvers that pilots could make when flying a plane and they would always remain conscious.

Increasing the force of gravity would be a unique and sure-fire security system to stop theft of valuable objects. If you increased the force of gravity on a valuable item, the thief would not be able to take it because it would be too heavy. There would have to be some type of system to ensure that no one would be able to change the force of gravity on the item of value.

A lower level of gravity would allow for easier transportation of goods and personal travel. For example, trucks need gas to move the mass of the objects inside the truck. Because there would be less gravity, it would take less energy to move the cargo in the truck, which would decrease fuel consumption. This would also decrease the amount of contact between the road and the tires. Roads would last longer and require less maintenance.

Disregarding the anti-gravity bubbles, the current laws of physics may or may not still apply when the universal gravitational constant changes. Since it is most likely that the universe would collapse upon itself into a singularity, similar to the conditions at the time of the big bang, it is difficult to predict how the universe would interact with itself. Scientists believe that the laws of physics that govern the universe today do not work in such extreme conditions. Some theories suggest that all of the forces in the universe combine into one force, so Newton’s gravitational constant and his equation of universal gravitation would probably not work.

and here's another calculation we put in, we did about 10 or something. I am not sure if this is the same one i put above but anyways:

Calculating the time it takes for Earth to reach the Sun with the new universal gravitational constant.

The force of gravity is the only force acting upon the Earth and is therefore the net force. The acceleration towards the Sun can then be calculated. As the Earth gets closer to the Sun (Δd decreases), the force of gravity will increase and so will the acceleration. Assume that the average acceleration of the entire trip, as constant acceleration, accurately represents the changing acceleration of what is actually happening. Also assume that the radius of the Earth and the Sun remain what they currently are (they have not collapsed into themselves with the increased gravity) and use the average distance of the Earth from the Sun. Calculating average acceleration, which will be the average of when Earth is at its current position and when it reaches the surface of the Sun:

Current position:
mE = 5.98x1024 kg
msun = 1.99x1030 kg
Δd = 1.50x1011 m
G = 6.67x1011 N•m2/kg2
Fg = ?

Fg = G * mE * msun / Δd2
Fg = 6.67x1011 N•m2/kg2 * 5.98x1024 kg * 1.99x1030 kg / (1.50x1011 m)2
Fg = 3.53x1044 N

At surface of Sun (where distance between centres is radius of Sun + radius of Earth):
mE = 5.98x1024 kg
msun = 1.99x1030 kg
Δd = 6.38x106 m + 6.96x108 m = 7.0238x108 m
G = 6.67x1011 N•m2/kg2
Fg = ?

Fg = G * mE * msun / Δd2
Fg = 6.67x1011 N•m2/kg2 * 5.98x1024 kg * 1.99x1030 kg / (7.0238x108 m)2
Fg = 1.61x1049 N

Average acceleration:
FNet = (Fg1 + Fg2) / 2
FNet = (3.53x1044 N + 1.61x1049 N) / 2
FNet = 8.05x1048 N

FNet = ma
a = FNet / mE
a = 8.05x1048 N / 5.98x1024 kg
a = 1.35x1024 m/s2



Assuming constant acceleration, the time the Earth takes to reach the Sun from its current position can now be calculated. Also assume that there is only one component to the Earth’s motion, which is towards the Sun, ignoring any of the orbital velocity it had at the beginning (making the initial velocity toward the Sun = 0):
a = 1.35x1024 m/s2
Δd = 1.50x1011 m
v1 = 0
Δt = ?

Δd = v1Δt + ½aΔt2
Δt = sqrt(2Δd / a)
Δt = sqrt(2(1.50x1011 m) / 1.35x1024 m/s2)
Δt = 4.71x10-7 s

Therefore it will take the Earth 4.71x10-7 s to reach the Sun.

Calculating the speed the Earth is traveling when it reaches the Sun.

v1 = 0
Δd = 1.50x1011 m
a = 1.35x1024 m/s2
v2 = ?

v22 = v12 + 2aΔd
v2 = sqrt(2(1.35x1024 m/s2)(1.50x1011 m))
v2 = 3.36x1017 m/s

Therefore, the Earth will be traveling 3.36x1017 m/s when it reaches the Sun.

Calculating the time it takes for Pluto to reach the Sun with the new universal gravitational constant.

Same assumptions as with Earth, calculate average acceleration:

Current position:
mPluto = 1.31x1022 kg
msun = 1.99x1030 kg
Δd = 5.89x1012 m
G = 6.67x1011 N•m2/kg2
Fg = ?

Fg = G * mE * msun / Δd2
Fg = 6.67x1011 N•m2/kg2 * 1.31x1022 kg * 1.99x1030 kg / (5.89x1012 m)2
Fg = 5.01x1038 N

At surface of Sun (where distance between centres is radius of Sun + radius of Pluto):
mPluto = 1.31x1022 kg
msun = 1.99x1030 kg
Δd = 1.18x106 m + 6.96x108 m = 6.9718x108 m
G = 6.67x1011 N•m2/kg2
Fg = ?

Fg = G * mE * msun / Δd2
Fg = 6.67x1011 N•m2/kg2 * 1.31x1022 kg * 1.99x1030 kg / (6.9718x108 m)2
Fg = 3.58x1046 N

Average acceleration:
FNet = (Fg1 + Fg2) / 2
FNet = (5.01x1038 N + 3.58x1046 N) / 2
FNet = 1.79x1046 N

FNet = ma
a = FNet / mPluto
a = 1.79x1046 N / 1.31x1022 kg
a = 1.37x1024 m/s2

Assuming constant acceleration, the time Pluto takes to reach the Sun from its current position can now be calculated. Also assume that there is only one component to Pluto’s motion, which is towards the Sun, ignoring any of the orbital velocity it had at the beginning (making the initial velocity toward the Sun = 0):
a = 1.37x1024 m/s2
Δd = 5.89x1012 m
v1 = 0
Δt = ?

Δd = v1Δt + ½aΔt2
Δt = sqrt(2Δd / a)
Δt = sqrt(2(5.89x1012 m) / 1.37x1024 m/s2)
Δt = 2.93x10-6 s

Therefore it will take Pluto 2.93x10-6 s to reach the Sun.

Calculating the speed the Pluto is traveling when it reaches the Sun.

v1 = 0
Δd = 5.89x1012 m
a = 1.37x1024 m/s2
v2 = ?

v22 = v12 + 2aΔd
v2 = sqrt(2(1.37x1024 m/s2)(5.89x1012 m))
v2 = 4.02x1018 m/s

Therefore, Pluto will be traveling 4.02x1018 m/s when it reaches the Sun.

Calculating the acceleration due to gravity on Earth.

Again, assume the radius of the Earth remains constant. Also, the object’s mass does not affect its acceleration due to gravity. Calculate acceleration due to gravity on Earth with new universal gravitational constant:

G = 6.67x1011 N•m2/kg2
mE = 5.98x1024 kg
∆d = 6.38106 m
g = ?

Fg = G * m1 * mE / ∆d2
M * g = G * m1 * mE / ∆d2
g = G * mE / ∆d2
g = 6.67x1011 N•m2/kg2 * 5.98x1024 kg / (6.38x106 m)2
g = 9.80x1022 m/s2


Calculating how much more energy can be generated by waterfalls.

Assume that the gravitational potential energy of the water at the top of the waterfall equals its kinetic energy at the bottom (no energy is lost). Also assume that the force of gravity (and acceleration due to gravity) does not change as the water gets closer to Earth. For this calculation use 1.0kg of water falling from a waterfall 100m tall. For normal conditions:

g = 9.8 m/s2
m = 1.0 kg
h = 100m
Eg = ?

Eg = mgh
Eg = (1.0 kg)(9.8m/s2)(100m)
Eg = 980 J

Under normal conditions, one kilogram of water has 980J of energy at the top of a 100m high waterfall.


With the new gravitational constant and the new acceleration due to gravity (calculated above), calculate the energy that 1.0kg of water has at the top of a 100m waterfall:
g = 9.80x1022 m/s2
m = 1.0 kg
h = 100m
Eg = ?


Eg = mgh
Eg = (1.0 kg)( 9.80x1022 m/s2)(100m)
Eg = 9.80x1024 J

Under the new conditions, one kilogram of water has 9.80x1024 J of energy at the top of a 100m high waterfall.

Calculate how much more energy the water has under these new conditions:
9.80x1024 J / 980 J
=1.0x1022

Therefore the water has 1.0x1022 times more energy at the top of the waterfall.
Since no energy was lost as the water fell, its kinetic energy at the bottom of the waterfall equals its Eg at the top. Therefore 1.0x1022 times more electrical energy can be generated by a turbine at the bottom of the waterfall, assuming the turbine is 100% efficient.

As you can see we assume a lot lol i hope this whole psot shows up.

 

[Ulysees]

i guess i will learn REAL physics when i go to university

Actually you will only learn more widely applicable mental models of physical things, but the absolute truth you will not learn: just like in the year 1900 there was no such thing as relativity taught in universities, likewise today there is no such thing as the physics of 2100 taught in universities. Does that mean all physics is wrong and there is no REAL physics? No, it means you have to remember the context of a problem, eg Newton is great for the motion of the planets, special relativity is better for fast moving things, quantum physics is useful for very small things, future physics is great for something as yet unknown, and so on. So you're in the context of Newton's equations, you use them, you bend them as suggested. At university you could do the same with more involved laws. Teachers at university are just as entitled as your High School teacher to ask hypothetical questions bending the laws of their respective physics, as an exercise promoting original thinking.

 

[jackster18]

We also took some cool vids of of youtube about space, black holes and stuff and the teacher liked it, also we made a newreport video saying what was going to happen. Heres the websites if you want to see the videos

im only able to post urls after 15 posts :( that's no good.

 

[rbj]

Actually you will only learn more widely applicable mental models of physical things, but the absolute truth you will not learn: just like in the year 1900 there was no such thing as relativity taught in universities,

no, but the Newtonian physics taught then is just as applicable today, for the domain where it was applied (speeds much slower than c and masses much larger than those of atomic particles).

likewise today there is no such thing as the physics of 2100 taught in universities.

i think they'll be teaching something about quantum mechanics and relativity in 2100, just as they are teaching some of the physics of 1700 in 2008.

At university you could do the same with more involved laws. Teachers at university are just as entitled as your High School teacher to ask hypothetical questions bending the laws of their respective physics, as an exercise promoting original thinking.

And, whether jackster approves or understand or not. It is not an issue of "bending the laws" or violating the laws of physics to see what happens. It is the operational meaninglessness of the question that you don't get and your ignorance (and that of the teacher) has been transmitted to jackster (which either he'll have to unlearn someday or he'll screw up like the science reporters of NY Times and he'll be caught with his pants down).

It is "bending the laws" to ask "what would happen if the mass ratio of protons to electrons changed significantly?" That is a meaningful question and since that ratio can't change, as far as I know, saying that it does represents a violation of physical law. But it's a violation that actually means something.

Asking "what would happen if the mass of the proton changed as well as all other particles in the same way?" That (as explicitly pointed out by Barrow) is a meaningless question. If you say that you created a model that demonstrates qualitatively how life would be different, the fact is your model or your interpretation of it is flawed. And this is what you did, if you say that you changed G, and nothing but G, and you came up with a model that shows that some lengths have gotten smaller while others have gotten longer, then I can say with complete confidence that, because there was a meaningful discriminatory difference (the ratio of those lengths changed), there must have been a meaningful cause (a ratio of like-dimensioned parameters changed). That means you changed something other than just G whether you realize or admit it or not.

jackster, you and your teacher and Ulysees may continue on in your bliss. I have done my best to try to hold the line on this encroachment of fallacy. other than maybe DaleSpam or some other regular, i haven't had any help, but have you noticed that the PF mentors didn't come down on me for propagating garbage?