B Does the Torricelli Vacuum Experiment Prove the Strength of Vacuum Forces?

[Rotating Wave]

TL;DR Summary

I watched this video ( https://youtu.be/rKPv8zApee0 ) and these questions arose:
What is a vacuum if not a space devoid of things?
How did this experiment show there was a vacuum and not merely a different kind of "pressure" (or something else)?

If Evangelista Torricelli truly created a vacuum, then there would be nothing in it, yet you can see through it which means light is obviously still in there (and who knows what else), right?
If there was truly nothing in it, and glass is a highly viscous fluid, and fluids conform to fill empty space, wouldn't the glass have collapsed or deformed to fill that nothingness fairly quickly (for glass) without something holding it in place? Or are the forces holding the glass together stronger than whatever force that creates a vacuum? (What force DOES create a vacuum?)
If it IS empty, wouldn't light behave differently than in a glass filled with air, since there are no particles to distort its path, as it were?

 

[BvU]

Hi,

I watched this video

I didn't, because it takes a full hour to watch.

What is a vacuum if not a space devoid of things?

answers: nothing ( !)

How did this experiment show there was a vacuum and not merely a different kind of "pressure" (or something else)?

Actually there is a very low pressure water vapour. So low that it's a vacuum for our perception.

which means light is obviously still in there (and who knows what else), right?

light goes through . Nothing else in there except the aforementioned water vapour molecules.

If there was truly nothing in it, and glass is a highly viscous fluid, and fluids conform to fill empty space, wouldn't the glass have collapsed or deformed to fill that nothingness fairly quickly (for glass) without something holding it in place?

I suppose a few millenia should do the trick, yes.

What force DOES create a vacuum

Hard to answer. Basically you have to remove everything that's there. The last bits are really difficult (theoretically probably imposssible)

"A mechanical force" is an inadequate answer: in physics that's not a fundamental force. But you have to do something to prevent a vacuum from getting filled, so you want to keep away stuff from it. Electromagnetic and gravitational force can help.

If it IS empty, wouldn't light behave differently than in a glass filled with air, since there are no particles to distort its path, as it were?

Correct. The breaking index of air depends on the pressure.

Keep up the good questions !

 

[Rotating Wave]

Hi,

I didn't, because it takes a full hour to watch.
answers: nothing ( !)
Actually there is a very low pressure water vapour. So low that it's a vacuum for our perception.

light goes through . Nothing else in there except the aforementioned water vapour molecules.
I suppose a few millenia should do the trick, yes.

Hard to answer. Basically you have to remove everything that's there. The last bits are really difficult (theoretically probably imposssible)

"A mechanical force" is an inadequate answer: in physics that's not a fundamental force. But you have to do something to prevent a vacuum from getting filled, so you want to keep away stuff from it. Electromagnetic and gravitational force can help.

Correct. The breaking index of air depends on the pressure.

Keep up the good questions !

Thank you. I feel better having those answers now. I wasn't sure about how fast glass actually flows, but wouldn't its speed increase in the inside at least and cause it to happen faster?
What if you took a vacuum tube and connected it in series to other vacuum tubes...
I need an on-call physicist. Lol
The smaller the volume of a tube the more "vacuum" you get out of it (given the same method at the same power per second), right?
If there was a vacuum strong enough to make a space of nothing, wouldn't it be just like a straw with one the closed while you vacuum the other end (it collapses together from the air pressure outside)? But, if it was a large enough and powerful enough vacuum it wouldn't just be air but even light, and that vacuum would be - for all intents and purposes - a "black hole."
Does that sound right? More important... IS it right? Are black holes vacuums? Is that something we would know yet?

 

[Rotating Wave]

I have another question, but I think it's an important one:
Does the water vapor in the vacuum tube 'gravitate' to the center, outer edges, top, bottom, or just float about as a gas normally does in a container?

 

[BvU]

The latter: completely normal. Gravity still does its work, so the minimal pressure higher up will be a hair less than lower down.

 

[Rotating Wave]

Travity still does its work, so the minimal pressure higher up will be a hair less than lower down.

Gravity still does its work, so the minimal pressure higher up will be a hair less than lower down.

Thank you. This has been very thought-provoking.

 

[sophiecentaur]

Thank you. I feel better having those answers now. I wasn't sure about how fast glass actually flows, but wouldn't its speed increase in the inside at least and cause it to happen faster?

One thing you should remember is that the pressure difference between an ' absolute' vacuum and ambient atmospheric pressure is very little different from the pressure difference between what a very modest laboratory vacuum pump can produce and ambient pressure. It's not the available force that limits how deep a vacuum you can produce, it's leaks and the 'compression ratio' or other limits of the pump and outgassing of the vessel and associated pipes. There are many clever strategies that can be used to sweep away the final few molecules that give you an ultra low vacuum; it's essentially an engineering problem - nothing fundamental.

 

[BvU]

But, if it was a large enough and powerful enough vacuum it wouldn't just be air but even light, and that vacuum would be - for all intents and purposes - a "black hole."

You mean : if you empty a volume completely, absolutely and totally, would it look dark ?
Because the answer to that question is: no, it would be completely transparent. The breaking index is 1 exactly.

A black hole is something completely different (Monty Python would say). Almost the exact opposite of a vacuum: you can't be further away from vacuum than in a black hole (but I am a mere physicist, not a BH expeert...)

 

[Rotating Wave]

You mean : if you empty a volume completely, absolutely and totally, would it look dark ?
Because the answer to that question is: no, it would be completely transparent. The breaking index is 1 exactly.

A black hole is something completely different (Monty Python would say). Almost the exact opposite of a vacuum: you can't be further away from vacuum than in a black hole (but I am a mere physicist, not a BH expeert...)

2 questions:
1 what is a "breaking index"? Does that have to do with angle of incident?

2.) Have we witnessed anything actually go INTO a black hole? Or is that based solely on math assuming gravity (and mass) is responsible?

 

[sophiecentaur]

1 what is a "breaking index"? Does that have to do with angle of incident?

I never heard of a breaking index - it could perhaps be Braking Index - i.e. slowing down the light. A bit quaint old fashioned terms. I think.

 

[Rotating Wave]

Also...
Do we create *constant* vacuums or *static* vacuums (where a constant vacuums is the continual emptying of the space and static is a vacuum is created then left to be)?

Can I use any mass object greater than 1 pascal for this experiment (as long as it blocks off anything from coming into the container), or does it have to be fluid? Or is there another factor i neglected?

I'm sorry for all the questions. My brain is constantly punching me with inquiries and obsessing over them. And they seem like they're not related to observers, but actually tie into each other subtly but require learning so many different areas to be satisfied...
Sorry, thought momentum.

 

[sophiecentaur]

Can I use any mass object greater than 1 pascal for this experiment (as long as it blocks off anything from coming into the container), or does it have to be fluid? Or is there another factor i neglected?

A mass doesn't have Pressure (pascals). Are you proposing to use a long rod of metal in place of the mercury column? Sounds a bit like a VacuVin??
The other factor is that you need a good (perfect) seal and a solid piston would let you down. But, if you want a really deep vacuum, you have to go to a lot of trouble. The mercury and the glass will be full of impurities that will boil off into the void.

Static and constant are not terms I've come across in this context. To maintain a very low vacuum, you need to keep pumping all the time because there is always another molecule to deal with. The vacuum, of deep space is pretty low - with an estimated single proton in a metre cube,

 

[Rotating Wave]

I never heard of a breaking index - it could perhaps be Braking Index - i.e. slowing down the light. A bit quaint old fashioned terms. I think.

Ok, I looked it up (braking index) and it has to do with pulsars and gravitational waves, it appears.
That's something beyond my ability to understand at this time, but it definitely plays into other thought experiments.

 

[Rotating Wave]

A mass doesn't have Pressure (pascals). Are you proposing to use a long rod of metal in place of the mercury column? Sounds a bit like a VacuVin??
The other factor is that you need a good (perfect) seal and a solid piston would let you down. But, if you want a really deep vacuum, you have to go to a lot of trouble. The mercury and the glass will be full of impurities that will boil off into the void.

Static and constant are not terms I've come across in this context. To maintain a very low vacuum, you need to keep pumping all the time because there is always another molecule to deal with. The vacuum, of deep space is pretty low - with an estimated single proton in a metre cube,

I know I wasn't using technical terms, that's why I defined their meaning as I did. And, yes, the "metal bar" concept is close to what I was thinking. It sounds like that means it can be done.

But, I shifted gears a little. Space is our most perfect vacuum, correct? So... so many questions. If space is a vacuum... do we know what MAKES it a vacuum? Is it because of the expansion of the universe?
And, does that mean that space is "nothing" or that it is a type of "energy" or "force" that occupies any area matter could but does not, to stabilize the vacuum pressure (parts per cubed metre)? I mean, I read that virtual particles and antiparticles are randomly created and annihialated in such a short span that they are considered to not be created or destroyed. This means they appear in the same space, right?
anyway, if space naturally tries to maintain a "vacuum equilibrium," as it were, wouldn't that mean it would have to push particles out of it to prevent the parts per cubed meter from increasing? Or do we understand why they do this already and I missed that part?
also, how small is the smallest vacuum we have made?

 

[BvU]

2 questions:
1 what is a "breaking index"? Does that have to do with angle of incident?

2.) Have we witnessed anything actually go INTO a black hole? Or is that based solely on math assuming gravity (and mass) is responsible?

1 My mistake. Non-native blabla etc. Correct term is index of refraction. The link in post #2 was correct, though!

However, seem to remember refraction has to do with breaking (latin: frangere)​

Point is: light travels with speed exactly $c$ in vacuum, $\displaystyle {c \over n}$ -- with $n$ the index of refraction -- elsewhere

2. Whole stars are gobbled up by black holes. I googled 'black hole devours star' and got this

how small is the smallest vacuum we have made?

Perhaps in high energy physics colliders ? Here is a link to the largest vacuum system in the world

 

[jbriggs444]

A black hole is something completely different (Monty Python would say). Almost the exact opposite of a vacuum: you can't be further away from vacuum than in a black hole (but I am a mere physicist, not a BH expeert...)

A classical Schwarzschild black hole is vacuum everywhere. It is a vacuum solution.

2.) Have we witnessed anything actually go INTO a black hole? Or is that based solely on math assuming gravity (and mass) is responsible?

By definition, the event horizon of a black hole is a dividing line beyond which nothing can escape toward the exterior in the future. By definition, we cannot witness anything passing such a horizon. The news will never make it here.

 

[Rotating Wave]

1 My mistake. Non-native blabla etc. Correct term is index of refraction. The link in post #2 was correct, though!

However, seem to remember refraction has to do with breaking (latin: frangere)​

Point is: light travels with speed exactly $c$ in vacuum, $\displaystyle {c \over n}$ -- with $n$ the index of refraction -- elsewhere

2. Whole stars are gobbled up by black holes. I googled 'black hole devours star' and got this

Perhaps in high energy physics colliders ? Here is a link to the largest vacuum system in the world

Ok, that clarifies some things. Index of refraction was what I meant when I said, "angle of incident." I'm terrible at terminology usually.

I watched the black hole "devouring" the star, but it didn't seem as though anything actually went into it, even in slow motion/frame-by-frame; it looks like it just pulls it to it's edge and then everything stays there (or shoots off in one of those burst of radiation in the center and the edge of the accretion disc). How do we know anything is falling in? And, if it's all falling in at the same speed (faster than the speed of light within the event horizon), why does an accretion disc form at all? Especially, when some of the matter actually has to change direction from going into the event horizon to orbit the black hole as part of the disc?
What would it mean if the black hole was actually pushing matter out, rather than pulling it in? (Note: not saying it does, but what would it mean if it did?)

 

[jbriggs444]

And, if it's all falling in at the same speed (faster than the speed of light within the event horizon),

Nothing material ever travels faster than the speed of light compared to a local standard of rest.

A difficulty is that there is no such thing as a local standard of rest that is "stationary" within the event horizon of a black hole. Another difficulty is that the notion of speed based on a non-local standard of rest is ambiguous in curved space-time. Such notions can yield speeds greater than c but not faster than light. [No matter how big a number you get for the speed of a material object, a pulse of light will still pass it]

The bottom line is that it's meaningless to say that something is traveling faster than the speed of light unless one is prepared to do a lot of clarification about the coordinate system one is using to make the claim.

The geometry of a black hole is not something you can wrap a Euclidean intuition around.

 

[BvU]

I watched the black hole "devouring" the star, but it didn't seem as though anything actually went into it

And all this in a thread about Toricelli !

See a few more and become an expert ! Look forward to a million more questions, but not at 2 AM my time

!

$\$

 

[Rotating Wave]

A classical Schwarzschild black hole is vacuum everywhere. It is a vacuum solution.

By definition, the event horizon of a black hole is a dividing line beyond which nothing can escape toward the exterior in the future. By definition, we cannot witness anything passing such a horizon. The news will never make it here.

I got lost on "tensor". I looked it up and thought it was describing a vector until it said they, along with scalars, are things a tensor can map between.
Perhaps I should just let it rest.

But, I would like to state that, it seems against Occam's razor to assume we aren't getting a "message" from matter swallowed by the black hole (because it can't escape to get to us, if it is swallowed), yet when we observe it we CAN see that much of the star is dissipated in bursts, and seems to not reduce in volume otherwise. I had been under the impression that gravity was a "dip" in space that objects fall into; the steeper the dip, the more energy required to get out of the dip, and so a black hole's gravity, if it can prevent anything from escaping would have to have a nearly vertical slope of space-time, so even light "falls" through space faster than it's natural speed (and so, obviously, incapable of escaping; it can never reach escape velocity because it would require infinite energy). So, if everything is falling into the black hole, and space has a near vertical, or vertical, slope in the black hole's event horizon, yet some escapes from being swallowed by shooting off into space away from the BH before entering the event horizon, and the star was further than the edge of the accretion disc when it was pulled in (and rapidly) so space-time there had a significant slope already, matter would still pull into the event horizon at the same rate, right? But, suddenly, the slope just... "drops", yet the accretion disc is held in orbit? Is this because of the gravitational waves emitted (I know part of it is the linear velocity momentum "countering" the pull of gravity by nearly equalling the force, but how are they not pulled in with collisions, precessions, ionic repulsion, and/or whatever forces would add to their (directional) acceleration into the black hole)?
Are these bits of matter falling into different gravity "wells" whose slope is steep enough that the objects would have to climb the well in order to fall into the BH's? And how close would an object have to be before its own gravitational pocket/well merges with the black hole's until the slope was negative and it fell in? Or do gravitational wells not merge?

If you could cause the slope of space-time to be positive in a given position, or for its slope to be constant (y = mx+b = a constant), would that prevent an object from falling into the BH'S gravitational slope (assuming it has a slope perpendicular to the object's) or would it always be a downward slope because of vectoral behavior? If vectors can be used (or, perhaps, this is what the tensors are for (?)), is it possible for some object to have an upward, or upward but slightly angled, space-time curve/well that would cause them to fall toward the black hole, but at such an angle that it would not be drawn in but "jump over" the black hole instead? Or is it a rule that no object can have a positive slope in space-time (that is, space must always bends outward from a mass so that the object falls into it from all directions at once)?
I wish I already understood physics. There's just so much...

As for nothing material traveling faster than the speed of light compared to a local standard of rest:
In an event horizon, the space within, it would seem, operates on the same principle as the expansion of the universe - both have velocities faster than the speed of light. Also, both are "vacuums", in that matter cannot exist there; in space's edges because nothing could get to it (seemingly having a positive space-time slope, {or perhaps a vertical slope that moves and draws the rest of the the universe into it, thus expanding it...?}), and in a black hole because at that kind of velocity, according to my understanding, no material thing could remain physical as the energy required would be infinite, because the object falling would be doing so at or greater than the speed of light (as measured by slope and not actual speed) as it rides that slope down. Its potential energy would become so great, eventually, that it would be able to escape, if it had something to influence a change in direction, and if it could stay together with that much potential energy. But, energy creates heat, heat causes separation and breaks weak and strong bonds, and also increases the wavelength of a wave (meaning more energy). However, each waveform/mass would require differing amounts of energy to "level up" their wave energy, and would increase at different speeds so that all unique forms alter wave-forms at different rates. Wouldn't this cause all matter to become waves (I mean, independent waves, since everything is already a wave/group of waves anyway)? If so, then they would no longer be "material" and could, hypothetically, travel faster than the speed of light merely by approaching it, so long as something NOT affected by the speed of light limit "carries it along.
Believe it or not, this is the abridged version. I left a whole slew of questions and topics unaddressed. Like how interference and reinforcement of waves would come into play as a materia gained energy/mass/velocity. Or WHY things even have inertia/mass!
Sorry, I'll let you sleep. I've had 4 hours in the past three days because of these kinds of thoughts, so I doubt I will sleep much tonight either. But I hope you rest well and apologize again for the long-windedness and over-curiosity.

 

[sophiecentaur]

It sounds like that means it can be done.

But only in principle - as in any piston. Leakage will spoil the experiment.

do we know what MAKES it a vacuum?

It's the near-absence of matter in that vicinity. Nothing to do with the expansion of the Universe - just the fact that matter tends to clump together, due to mutual gravitational attraction. In deep space, any atoms are too far away from concentrations of mass for them to be affected 'significantly', although they are still actually attracted to the masses around them.

I feel that you are trying to address too many things at once. Physics is too big for that. You need to sort out one thing at a time (starting from the real basics). Cosmology will seem total gobbledegook if you don't have the basics. Boring, perhaps but I, personally, have always found the very first bits of Physics I learned are actually very interesting. It's like reading a good whodunnit; if you skip through and miss all the clues on the way then the denouement means nothing to you.

 

[Rotating Wave]

But only in principle - as in any piston. Leakage will spoil the experiment.

It's the near-absence of matter in that vicinity. Nothing to do with the expansion of the Universe - just the fact that matter tends to clump together, due to mutual gravitational attraction. In deep space, any atoms are too far away from concentrations of mass for them to be affected 'significantly', although they are still actually attracted to the masses around them.

I meant, why does the universe have a vacuum - what makes the matter be so far apart in the universe? But, that is of less significance right now. I understand the experiment better and even the fundamentals of a vacuum.
Again, I apologize for all the questions. One thought triggers the next, constantly, and my current understanding isn't enough to resolve them.

I feel that you are trying to address too many things at once. Physics is too big for that. You need to sort out one thing at a time (starting from the real basics). Cosmology will seem total gobbledegook if you don't have the basics. Boring, perhaps but I, personally, have always found the very first bits of Physics I learned are actually very interesting. It's like reading a good whodunnit; if you skip through and miss all the clues on the way then the denouement means nothing to you.

I believe you are correct about addressing too many things at once. To an extent. Every time I try to understand one concept, however, another concept associates somehow and I also need to understand that to understand what I originally was trying to understand.
l will close this thread now, I believe, and post other questions in their respective topic/forum, except to respond to comments here.

Thank you, everyone, for your input. I appreciate the knowledge and understanding you have shared.
Perhaps one day I will be able to communicate on the same level of understanding. But... for now, I need a direction to go. You said to go back to the basics. What are the basics?
I understand Newtonian physics moderately well, mechanical energy, conservation of motion, momentum, energy, mass, etc. I'm not sure where the "basics" end and the non-basics begin.

 

[jbriggs444]

But, I would like to state that, it seems against Occam's razor to assume we aren't getting a "message" from matter swallowed by the black hole (because it can't escape to get to us, if it is swallowed), yet when we observe it we CAN see that much of the star is dissipated in bursts, and seems to not reduce in volume otherwise. I had been under the impression that gravity was a "dip" in space that objects fall into; the steeper the dip, the more energy required to get out of the dip, and so a black hole's gravity, if it can prevent anything from escaping would have to have a nearly vertical slope of space-time, so even light "falls" through space faster than it's natural speed (and so, obviously, incapable of escaping; it can never reach escape velocity because it would require infinite energy).

Pretty much everything you talk about above is intuitive, heuristic and, ultimately, wrong. Gravity is not a dip in space. It is not a force. It does not pull. Space-time does not have a slope. There is nothing going at a great speed and energy becomes meaningless outside of a "stationary" space-time.

To get back to the question at hand -- "can we see stuff going into a black hole". We cannot see stuff passing the event horizon. That's part of the definition of the event horizon. If you could see stuff there, it wouldn't be the event horizon. Occam's razor has nothing to say about matters of definition.

There is no prohibition against seeing stuff go toward the presumed horizon, disappear from view and not re-emerge into view.

 

[Andy Resnick]

<snip>
glass is a highly viscous fluid
<snip>

Minor clarification- glass is not a viscous fluid, it is an amorphous solid. Evidence: prehistoric obsidian blades are still sharp.

 

[Rotating Wave]

Pretty much everything you talk about above is intuitive, heuristic and, ultimately, wrong. Gravity is not a dip in space. It is not a force. It does not pull. Space-time does not have a slope. There is nothing going at a great speed and energy becomes meaningless outside of a "stationary" space-time.

Please explain what gravity IS, rather than what it is not, then. What I hear you saying is that space-time does NOT have a curvature (because isn't a curvature a changing slope or series of slopes?) and that gravity does not actually exist. If gravity is not a force, then how does it affect anything? F=ma, correct? And G= G_k(m₁m₂/r²), where G is the magnitude of gravity, G_k is the constant force of gravity, or the equivalent of 'a' in F=ma, and 'm' is the product of two masses per the square of their radius. Does this not mean that gravity is a force? If it's not, then what is it? And why does the formula for forces determine it? What is a "force," then - how would you define it?
And, if something causes the effect of 'gravity' (for lack of a better term, since I don't know what to call the 'pull' (again, for lack of a better term) of masses if gravity doesn't pull), what is that thing?

Please explain what you mean that there is nothing going at a great speed. Light doesn't travel at a great speed?

More interestingly, why is energy meaningless outside of "stationary" space-time? What do you mean "stationary"? Do you mean stationary relative to other parts of the system, or stationary relative to other systems? Or something else altogether?

To get back to the question at hand -- "can we see stuff going into a black hole". We cannot see stuff passing the event horizon. That's part of the definition of the event horizon. If you could see stuff there, it wouldn't be the event horizon. Occam's razor has nothing to say about matters of definition.

I did not mean 'see' as in with our eyes, but 'detect'. I apologize for the poor terminology. I understand that light causes sight and, if it can't escape a black hole to get to us then we cannot possibly see it at that point. However, we are seeing light around the black hole, including its direction of travel. We visually see the light around the black hole, but cannot visually see light that enters the event horizon. I get that. But we can see, either visually or through some other receptive means (by this I count technology such as electron microscopes, telescopes, and the like, and even math as 'receptive' means) how that light is behaving PRIOR to entering the black hole. And, from all of the different sources I've viewed on this phenomenon, not one gives the appearance that light is traveling toward the event horizon to not be seen. It all approaches, from observation, the black hole and then orbits it. So, when I say, "Have we ever seen light enter a black hole," it isn't a reference to the light IN the black hole or past the event horizon, but the behavior of light that shows that it is, in fact, ENTERING the event horizon in the first place.
My apologies for the misunderstanding. I should not have use the word 'see' with something so directly related but having a different meaning.

There is no prohibition against seeing stuff go toward the presumed horizon, disappear from view and not re-emerge into view.

THIS is actually what I was referring to by saying 'seeing' light go into the black hole. How is it determined that it went into the black hole and was no longer observable? What instrumentation is used to observe the loss of... whatever is lost when light is swallowed, in the midst of all that energy/mass/light, etc.?

I came expecting to be wrong about things. I know my knowledge is limited. However, I also know that classical physics is wrong (not completely, or even mostly, but at least some) or it would be able to explain things that it does not yet (so 'wrong' in that it is, at the least, incomplete). My goal is to think outside the box, even if it goes against accepted principles, yet to understand the accepted principles as a working model to which I can compare the out-of-box hypotheses and prove/disprove them through the comparison. If the standard model fits, but the hypotheses comes up with a far off answer in comparison to the working model, then it is obviously not accurate.

Currently, I am questioning the idea that mass "creates" gravity. It requires a different approach if one assumes that it does not. However, simply because the working model explains behavior, does not mean that it is correct, or even that the causes are accurate, only that the math works on the assumptions we are using in the working model. It DOES mean that we have something to which we can compare new hypotheses or alternate models. I may be wrong in my hypotheses. I understand that these are simply causal possibilities, given that they can fit the same behavior as the standard model to the same accuracy or better, and that they will more than likely need to be discarded. But, without first examining their plausibility from many angles, I feel it would be foolish to just discard them because they don't fit the standard model.

However, this is not to say that they hold more weight in my mind than the standard models. The standard models work, so they make a good base for comparison. My hypothetical models carry more weight in my mind only in that they are more important for me to work on, due to their less developed nature. And they are, largely, based on what I learn from others discussing the topics, such as physics videos and reading material, including wikipedia, google and YouTube, along with the parts of physics in which I DO have a sufficient understanding - at least of the base concepts - from actual textbooks, courses, and papers.
For example, when I discussed the 'dip' in space, I was referring to Einstein's relativity theory that identifies gravity as a curvature of space-time, and when I discussed the 'slope' of space, I was referring to that curvature. But if there is no curvature/slope... How do I know which sources have accurate information if even fundamentals like this are not accurate and all the sources I view, reported to be factual, describe it in this way?
I am HSAF/ADHD and have issues communicating what I mean, even when the concept is clear by context, so I often use the wrong terms when trying to explain something. I don't mean to, it just happens. I will try to be more accurate with my terminology and more precise at explaining concepts as meant, but I can't make any promises that I will make the attempt successfully

Minor clarification- glass is not a viscous fluid, it is an amorphous solid. Evidence: prehistoric obsidian blades are still sharp.

I do recall hearing this now that you mentioned it, though I never would have thought of the term "amorphous solid" trying to recall it.
Thank you. That does make a difference in the way I see things.

 

[BvU]

l will close this thread now, I believe, and post other questions in their respective topic/forum, except to respond to comments here.

Do I spot a contradiction here ?

Please explain what gravity IS, rather than what it is not, then. What I hear you saying is that space-time does NOT have a curvature (because isn't a curvature a changing slope or series of slopes?) and that gravity does not actually exist. If gravity is not a force, then how does it affect anything?

You do a pretty good job yourself ! (*) :

$F=ma$, correct? And $$ G= G_k{m_1 m_2\over r^2}\ ,$$where $G$ is the magnitude of gravity, $G_k$ is the constant force of gravity, or the equivalent of '$a\,$' in $F=ma$, and '$m$' is the product of two masses per the square of their radius.

but here you derail spectacularly:
$$ F = G_k{m_1 m_2\over r^2}$$ where $F$ is the magnitude of gravitational force, the equivalent of '$F\,$' in $F=ma$ !

And $G_k$ is not a force but the gravitational constant with a completely other dimension. The value of $G_k$ says something about the relative strength of gravity.

Does this not mean that gravity is a force? If it's not, then what is it? And why does the formula for forces determine it? What is a "force," then - how would you define it?

Yes, apparently.

And, if something causes the effect of 'gravity' (for lack of a better term, since I don't know what to call the 'pull' (again, for lack of a better term) of masses if gravity doesn't pull), what is that thing?

mass.
(*) in the sense that you describe the effects. To a very large extent, that is what physics is all about.

The questions 'why' and 'what IS it ?' are better left to philosophers.

Have to hand it to you, you ask some pretty tough questions !

 

[epenguin]

Glass does flow and examples can be seen in e.g. in antique windows where, however, it has taken several centuries at ordinary temperatures. I would think that in good quality laboratory glass it is slower.

Something like your question about light did exercise early scientists. Some of this is by memory, however certainly Robert Boyle (second half of 17th century) developed a pump where you could actually achieve and work with a decent vacuum. As has been pointed out, this is a question of degree and you can never get a perfect vacuum, Boyle could just get a better one in a larger volume than anyone ever had before.This allowed him to clarify things that were not clear before, but that we take for granted and suppose to be obvious.Even the idea that air is a substance was only emerging, and that there were other gases than air was clarified only slowly. I'm pretty sure that it was Boyle who shook a bell inside his vacuum and found that no sound was heard. From this he concluded that the substance, air, was needed for the transmission of sound. On the other hand he could see still see the bell inside the vacuum in the glass container. So either nothing was needed for the transmission of light, or there was still some other substance through which it could be transmitted. When a couple of centuries later there came to be a better theory of light, they still could not get over this idea and postulated that there was some mysterious pervading substance, a very unsubstantial substance to which they gave the somewhat mystical name Aether, through which light waves could be carried a bit as airwaves carried in air. They made calculations about this aether which have finished in the dustbin of scientific history, And these days we are clear that we do not need any aether and that the light is all carried on fields, which we all understand extremely well, they are, well we all understand them extremely well.

 

[sophiecentaur]

Glass does flow and examples can be seen in e.g. in antique windows where, however, it has taken several centuries at ordinary temperatures. I would think that in good quality laboratory glass it is slower.

IIRC, that is myth. Old glass was made by an 'old' method and was of varying thickness. Glaziers used to put it all 'thick end down' - probably to standardise things so any refraction was at least the same from pane to pane. (Less to distract the congregation during long sermons, perhaps.)

Also, if glass (any glass) was in the habit of flowing measurably then the massive old victorian telescope lenses would all have gone well out of spec within the subsequent years.

 

[BvU]

From the @sophiecentaur link:

A mathematical model shows it would take longer than the universe has existed for room temperature cathedral glass to rearrange itself to appear melted.

So I have misled everyone with

I suppose a few millenia should do the trick, yes.

(I too had this fluid misconception that @Andy Resnick corrected in post #24 )

 

[sophiecentaur]

I too had this fluid misconception

But if you read it enough times, it becomes true. Everybody learned about stained glass windows and nobody put them straight. (Glass is an amorphous solid at room temperature and not a supercooled liquid) The real story is actually just as fascinating, with the technique of drawing large cylinders of molten glass (lovely video), cutting them and flattening them. Loads of money to be made for modern suppliers of glass made this way.

 

[Rotating Wave]

Glass does flow and examples can be seen in e.g. in antique windows where, however, it has taken several centuries at ordinary temperatures. I would think that in good quality laboratory glass it is slower.

Something like your question about light did exercise early scientists. Some of this is by memory, however certainly Robert Boyle (second half of 17th century) developed a pump where you could actually achieve and work with a decent vacuum. As has been pointed out, this is a question of degree and you can never get a perfect vacuum, Boyle could just get a better one in a larger volume than anyone ever had before.This allowed him to clarify things that were not clear before, but that we take for granted and suppose to be obvious.Even the idea that air is a substance was only emerging, and that there were other gases than air was clarified only slowly. I'm pretty sure that it was Boyle who shook a bell inside his vacuum and found that no sound was heard. From this he concluded that the substance, air, was needed for the transmission of sound. On the other hand he could see still see the bell inside the vacuum in the glass container. So either nothing was needed for the transmission of light, or there was still some other substance through which it could be transmitted. When a couple of centuries later there came to be a better theory of light, they still could not get over this idea and postulated that there was some mysterious pervading substance, a very unsubstantial substance to which they gave the somewhat mystical name Aether, through which light waves could be carried a bit as airwaves carried in air. They made calculations about this aether which have finished in the dustbin of scientific history, And these days we are clear that we do not need any aether and that the light is all carried on fields, which we all understand extremely well, they are, well we all understand them extremely well.

On this matter... Doesn't that mean that a "field" IS the aether they were looking for? I mean, they were looking for the medium light is carried through, and we now know it is carried on fields, so we basically just renamed 'aether' to 'field', right?
And, I did not know about this experiment, but I did know about the concept of the aether. But I will investigate this experiment because it looks to hold much information.

 

[Rotating Wave]

Do I spot a contradiction here ?

You do a pretty good job yourself ! (*) :
but here you derail spectacularly:
$$ F = G_k{m_1 m_2\over r^2}$$ where $F$ is the magnitude of gravitational force, the equivalent of '$F\,$' in $F=ma$ !

And $G_k$ is not a force but the gravitational constant with a completely other dimension. The value of $G_k$ says something about the relative strength of gravity.

Yes, apparently.

mass.
(*) in the sense that you describe the effects. To a very large extent, that is what physics is all about.

The questions 'why' and 'what IS it ?' are better left to philosophers.

Have to hand it to you, you ask some pretty tough questions !

I'm sorry about the tough questions thing. I didn't know they would be tough when I asked them.
I'm just trying to piece things together. I haven't been near information for very long and am trying to catch up.

 

[Rotating Wave]

Do I spot a contradiction here ?

You do a pretty good job yourself ! (*) :
but here you derail spectacularly:
$$ F = G_k{m_1 m_2\over r^2}$$ where $F$ is the magnitude of gravitational force, the equivalent of '$F\,$' in $F=ma$ !

I am confused to how this is different than what I said: "...where G is the magnitude of gravity, Gk is the constant force of gravity, or the equivalent of 'a' in F=ma, and 'm' is the product of two masses per the square of their radius."
If G_k is not F, and {m_1 m_2\over r^2} is not F, then G (the magnitude of gravity, or gravitational force) would also be F, so I was saying also that G is F. So I am not sure how I derailed on that one. Please clarify?

 

[BvU]

G is not the magnitude of gravity. It is the magnitude of the gravitational force.

$G_k$ is the gravitational constant. It is NOT the equivalent of $a$ in $F = ma$.
The dimension of $G_k$ is length³ x mass^-2 x time^-2, units Nm²/kg².
The dimension of 'a' is length x time^-2, units m/s² .
Totally incomparable.

And 'm' is a mass, in kilogram, NOT the product of two masses divided by the square of their distance: the latter has a dimension kg²/m², which is incomparable.

 

[BvU]

In a textbook you can find the equivalent you are seeking:

If we use the mass and radius of the earth, we can write $$g = {G_k\, m_{\text earth} \over r_{\text earth}^2}$$ and THEN $g$ is an acceleration and $mg$ is a force.

https://en.wikipedia.org/wiki/Gravitational_constant#Definition

$\$

 

[Rotating Wave]

G is not the magnitude of gravity. It is the magnitude of the gravitational force.

$G_k$ is the gravitational constant. It is NOT the equivalent of $a$ in $F = ma$.
The dimension of $G_k$ is length³ x mass^-2 x time^-2, units Nm²/kg².
The dimension of 'a' is length x time^-2, units m/s² .

And 'm' is a mass, in kilogram, NOT the product of two masses divide by the square of their distance: the latter has a dimension kg²/m², which is incomparable.

Ok. I see! Thank you. I guess I have more studying to do.

 

[Rotating Wave]

In a textbook you can find the equivalent you are seeking:

If we use the mass and radius of the earth, we can write $$g = {G_k\, m_{\text earth} \over r_{\text earth}^2}$$ and THEN $g$ is an acceleration and $mg$ is a force.

https://en.wikipedia.org/wiki/Gravitational_constant#Definition

$\$

Yeah, I need to study more. It makes sense. I appear to have concepts mixed up. I didn't realize G_k had a different dimensional property though, now I can see how I should have known from reverse engineering the math.
Ok. So it looks like I'll be hitting the basics again to solidify the concepts.

 

[StandardsGuy]

answers: nothing ( !)
Actually there is a very low pressure water vapour. So low that it's a vacuum for our perception.

I disagree. A vacuum contains all the laws of the universe. It may be in the form of fields such as the Higgs field. That's a lot more than nothing.

 

[BvU]

A vacuum contains all the laws of the universe

Don't forget dreams, hope and charity.

I wholeheartedly disagree, but you are entitled to your opinion. Any experimental evidence ?

 

[Rotating Wave]

Don't forget dreams, hope and charity.

I wholeheartedly disagree, but you are entitled to your opinion. Any experimental evidence ?

I think I get what Standards guy is saying. Space is a vacuum and holds all of the laws of the universe (because it basically IS the universe), so any artificial vacuum - like Torricelli's - would have those same traits, including fields.
In that case, space is the experimental evidence of a vacuum having all the laws of physics.
I think that's what they were saying...