Does Space Expand? What Do You Think?

[marcus]

No, it's not increasing distance between 2 galaxies that is the problem. It is increasing distances between ALL galaxies! How can this be? Do we really know?

I can't tell you the REAL TRUTH I can just tell you how it looks. The universe looks amazingly uniform, and same largescale scattering of galaxies in whatever direction.

do some simple picture-math. make a uniform distribution of dots on a piece of paper and suppose that you are on one dot and the distances to all the other dots are increasing by 1 percent each day

then you will find that the distances between any two dots must be increasing 1 percent per day.

it is like similar triangles in 9th grade trig. If the distance from A to B increases 1 percent and the distance A to C increases 1 percent then if the triangle stays same shape the distance from B to C must also increase by same proportion.

It's damn frustrating! Nothing adds up! Does the universe curve round on itself? Or is it flat & infinite? What is going on? Why aren't people disturbed?

I am not sure you are serious It doesn't matter to what we were talking about whether space is finite or infinite. Locally the expansion looks the same. We can tell that if it is finite then it is very very large.
All the evidence points towards expansion continuing indefinitely. What's to worry?
Why be disturbed?

Are you sure you are not exaggerating?

 

[wolram]

I think a lot of the confusion about expansion would stop if we had some idea of the total energy the universe has within it, and what these energies do, pull, push.

 

[mattex]

What's to worry? Why be disturbed?

Are you sure you are not exaggerating?

Well, I'm one of those poor sods who suffers this universe - something in my genes, perhaps. I've never really understood why others don't have this emotional reaction also? I've always put it down to self-denial, or something...

So no, I'm not really exaggerating when I say this universe terrifies me at times. What is ultimately going on? It's cruel if you ask me.

 

[marcus]

...something in my genes, perhaps. I've never really understood why others don't have this emotional reaction also? ...this universe terrifies me at times...

I am delighted that you have an emotional reaction to the universe and are open about it.
We can't talk too much about our emotional relations to nature and the universe, here, or the thread will be moved to some more literary or philosophical forum. So be restrained.

However I think it is human nature to relate emotionally to the universe and I do that myself, but with a different attitude. I deeply love it. I totally admire its lawfullness. I am also very glad that in the view of modern cosmology the universe is not expected to eventually collapse (I thought it was very sad when they were predicting a big crunch.)

According to modern understanding of gravity, the ONLY WAY IT CAN AVOID COLLAPSE is to continue expanding. Fortunately this is what it seems inclined to do!
Moreover it is expanding in a rather gentle regular way----the horror stories which sensationalist fringe scientists make up about catastrophic expansion or "big rip" are not accepted by mainstream. Honestly we could hardly have it better.

And we are only beginning to find out the real laws of physics. All we have now are rough approximations (though even they are elegant) and must always be trying to improve them, to get closer to the real laws.

that is my attitude. You have yours, which is one of dread. Any attitude, if it is genuine, is valid, I believe. There is no "correct" one.

Be well, and try to ask only scientific questions in the scientific forums.

 

[Chronos]

All our knowledge of the universe is indirect. The long and the short of it is we think it's expanding because of redshift - a fairly well established scientific principle called the doppler effect. Wipe that concept from the blackboard of science and most modern models of the universe are dead on arrival. The problem is, it does not easily erase. All other independent indicators of distance strongly agree with the redshift interpretation. Halton Arp has railed against the redshift interpretation for many years, but his arguments have not been well received. That does not falsify his claim, but places it squarely within the fringe camp.

 

[andrewj]

are there three fixed points

 

[everymanjack]

All our knowledge of the universe is indirect. The long and the short of it is we think it's expanding because of redshift - a fairly well established scientific principle called the doppler effect. Wipe that concept from the blackboard of science and most modern models of the universe are dead on arrival. The problem is, it does not easily erase. All other independent indicators of distance strongly agree with the redshift interpretation. Halton Arp has railed against the redshift interpretation for many years, but his arguments have not been well received. That does not falsify his claim, but places it squarely within the fringe camp.

The wavelength redshift of receding light is understandable. Inertia from the big bang must have propelled spacetime very fast. Looking back, we see light receding very fast into the past, and a lot of redshift. But how does that translate into present-tense "accelerating expansion"?

 

[ummani]

In 1982, I purchased a publication advertised in the magazine Scientific American; a book entitled The New Physics of Symmetrical Energy Structures (ISBN 0-910122-67-9). The –not for profit publication, The Theory of Symmetrical Energy Structures (SES) in a Megadimensional Cosmology and was produced by the Alpha Omega Research Foundation, Inc. The theory derives Planck length and all the physical constants, to the accuracy that we know π ! The Theory takes a single nucleon placed in the Earth's center and derives a new value for the gravitational constant G!
In October 1983 the Conference Generales des et Measures (CGPM) met in Paris to change the definition of the meter, where it was suggested they delay their decision until the theory had a proper evaluation.
My question is, why hasn’t there been a scientific revolution of unprecedented magnitude taken place? With this theory the all the forces have been unified, including gravity!

 

[Vanadium 50]

My question is, why hasn’t there been a scientific revolution of unprecedented magnitude taken place?

Because this book is crackpottery.

 

[yogi]

Sure, that's a pretty clear argument you present and I agree with you. However, there are many, including Peacock, as well as Martin Reese and Steven Wienberg who wrote a New Scientist article about this some years ago who contend that thinking in this way misleads you and it's better to just think kinematically.

The classic test case is this. Imagine you are in an expanding universe and hold a galaxy at rest with respect to you but at a cosmological distance. According to Hubbles law a galaxy at that distance should be receding but you prevent this by using a chain or rockets or something to hold it in place. If you let go of the galaxy, what does it do?


[THINK ABOUT THIS FIRST THEN READ ON]













The answer you may assume is that since space is expanding the galaxy will start moving away from you, joining the Hubble flow eventually. However in a decelerating (but still expanding) universe the particle actually comes towards you! If you think about it it becomes clear why but Peacock argues in the link I posted that it is the idea of expanding space that leads to these misconceptions and hence should be abandoned.

Stretching space and kinematical motion relative to space are not the only possibilities that can be conjured up to explain expansion -if space is granular on some scale, and the number of units per volume is increasing - then a tethered galaxy would pick up the Hubble flow when released because of the increasing number of spatial entities (whatever they might be - eg mico vortices and the like) - which multiply in proportion to the volume - consistent with exponential expansion internally driven rather than externally motivated

 

[nutgeb]

Yogi, please explain a little more about your idea. Are you saying that the increase in the number of granular units per volume creates a sort of positive pressure which in effect causes them to repel each other and solid matter, pushing everything apart? If so does that positive pressure bring additional gravity with it, like mass-energy does in GR? And how can positive pressure cause things to move apart if there isn't a pressure gradient somewhere (i.e., an outer 'edge' to the granule-filled universe, surrounded by a region devoid of granules)

Or are the granules just an instantiation of dark energy, characterized by negative pressure, which causes a sort of mutual anti-gravitational repulsion (as well as adding gravity)?

Dark energy of course is an explanation for the recent acceleration of the expansion rate, but it is not an explanation for the "original" expansion which was decelerating due to gravity until dark energy eventually became dominant. (Other than of course attributing inflation to some more powerful form of dark energy).

A model that requires both proliferating granules AND proliferating dark energy seems even more perplexing than the standard model.

I also note that the published analyses of the "tethered galaxy" exercise describe the idea of the untethered galaxy "picking up the Hubble flow" as a fallacy. Rather, unless dark energy dominates, the untethered galaxy moves counter to what the Hubble flow intuitively would cause. (Eventually the galaxy's peculiar velocity decays to the point where it arguably asymptotically "rejoins the Hubble flow", but this may be on the opposite side of the origin.) But you know that, so maybe I'm misinterpreting your comment.

 

[yogi]

Yogi, please explain a little more about your idea. Are you saying that the increase in the number of granular units per volume creates a sort of positive pressure which in effect causes them to repel each other and solid matter, pushing everything apart? If so does that positive pressure bring additional gravity with it, like mass-energy does in GR? And how can positive pressure cause things to move apart if there isn't a pressure gradient somewhere (i.e., an outer 'edge' to the granule-filled universe, surrounded by a region devoid of granules)

Or are the granules just an instantiation of dark energy, characterized by negative pressure, which causes a sort of mutual anti-gravitational repulsion (as well as adding gravity)?

Dark energy of course is an explanation for the recent acceleration of the expansion rate, but it is not an explanation for the "original" expansion which was decelerating due to gravity until dark energy eventually became dominant. (Other than of course attributing inflation to some more powerful form of dark energy).

A model that requires both proliferating granules AND proliferating dark energy seems even more perplexing than the standard model.

I also note that the published analyses of the "tethered galaxy" exercise describe the idea of the untethered galaxy "picking up the Hubble flow" as a fallacy. Rather, unless dark energy dominates, the untethered galaxy moves counter to what the Hubble flow intuitively would cause. (Eventually the galaxy's peculiar velocity decays to the point where it arguably asymptotically "rejoins the Hubble flow", but this may be on the opposite side of the origin.) But you know that, so maybe I'm misinterpreting your comment.

I really don't have a particular model in mind - maybe what I described is something in the nature of a plenum of quasi-static neutrino like angular momentums - jostling like atoms in a gas, and growing in number wherever stresses permit - there are many ways to envision a granular space - perhaps even with individual dimensions on the order of the Planck scale. My point was that stretching space and velocity wrt space are not exhaustive alternatives. As you might guess, I do have difficulties with the ad hoc standard model - I think its not good to get boxed in as far as explanations go given our inability to relate the tenants of the standard model to a physical form -in fact I don't even think it is altogether wise to blame gravity on curvature - while there appears to be little doubt that curvature exists - it may be consequent rather than causal - gravity may be an inertial reaction and curvature may be the evidence rather than the cause. GR started out with wrong presumptions, a positively curved static universe. To explain the G force - Einstein proposed that inert mass curves static space and time - well maybe it does -The standard model postulates dark matter and dark energy in amounts that agree with what appears to be good data - but the mechanism of expansion is not known - Prior to 1998 almost everyone was convinced the q = 1/2 universe had to be correct - so for me its worth exploring querky alternatives - how boring it would be if we already had all the answers.

 

[nutgeb]

OK, I see. Yes there are still lots of fundamental questions about the standard model, so it is possible it will be overturned or significantly modified in the future.

I share your uneasiness about the assertion that gravity curves spacetime. It is a wonderful mathematical model and makes for very accessible graphical representations. But as you say the converse doesn't seem to be ruled out either. As has been mentioned before, an arrow flying through a crosswind could be described as traveling through curved spacetime, merely following a geodesic. But is that really a meaningful physical statement in this context? It may just come down to whichever approach makes the metric easier to calculate.

GR seems to justify the application of highly abstract methodologies because of its weirder aspects -- time dilation and spatial curvature. Either something is happening to this entity called 'spacetime' at a very deep level, or else we're missing a cornerstone of how to otherwise describe these observed phenomena.

 

[yogi]

OK, I see. Yes there are still lots of fundamental questions about the standard model, so it is possible it will be overturned or significantly modified in the future.

I share your uneasiness about the assertion that gravity curves spacetime. It is a wonderful mathematical model and makes for very accessible graphical representations. But as you say the converse doesn't seem to be ruled out either. As has been mentioned before, an arrow flying through a crosswind could be described as traveling through curved spacetime, merely following a geodesic. But is that really a meaningful physical statement in this context? It may just come down to whichever approach makes the metric easier to calculate.

GR seems to justify the application of highly abstract methodologies because of its weirder aspects -- time dilation and spatial curvature. Either something is happening to this entity called 'spacetime' at a very deep level, or else we're missing a cornerstone of how to otherwise describe these observed phenomena.

Exactly - we have eased into the idea that inert matter affects static space - but we can't confirm that conclusion because we are living in a universe where matter is inertial and space is not only not static, rather it is dynamic in some sense - so what we observe might be the curvature or distortion of a momentum flow produced by interaction with the G field. Einstein did a great job with what was available at the time - some of which was wrong, yet the theory survived. I wonder what he would have concluded if he had any idea that the space was accelerating.

 

[Whitewolf4869]

What proof is there that space expands at all
That is just an assumption since you can't see it touch it or sense it in any way.

 

[GeorgeDishman]

What proof is there that space expands at all
That is just an assumption since you can't see it touch it or sense it in any way.

As has been said in this thread several times, the prime evidence is the spectral redshift of distant sources. The idea that this could be caused by some mechanism causing energy loss en route (a.k.a. Tired Light) is ruled out because the redshift is independent of frequency and because supernova light curves exhibit stretching compatible with the redshift (i.e. they are farther away by the time the light fades). Modelling it as a simple Doppler shift doesn't fit the gravitational models, the distance between us and a galaxy at z=2 should be increasing by more than 1 light year per year if they are correct. However, envisaging it as "expansion of space" fits perfectly, including several other tests. We adopt what works as our model and continue to look for discrepancies to improve it.

 

[Whitewolf4869]

So you are saying that expansion will eventually be the end of all because the vacuum of space will overcome gravidly.

 

[GeorgeDishman]

So you are saying that expansion will eventually be the end of all because the vacuum of space will overcome gravidly.

That's the way it looks at present. The effect of gravity slowing expansion depends on the average density of matter in space. As stuff gets farther apart, that density falls as the cube of the expansion. Vacuum energy (or whatever "dark energy" turns out to be) on the other hand seems to have constant density, every cubic metre of vacuum is the same as every other cubic metre. The two were roughly equal about 8 billion years ago and since then the rate of expansion has been increasing. As time goes on, the matter keeps gets thinner and that trend isn't going to reverse. Expansion has already won the contest.

 

[Whitewolf4869]

#1 The theory is all wrong vacuums don't expand
#2 So comparing space to balloons or bread is foolish
#3 Then an equation is created to explain what we see through our telescopes
#4 When that doesn't fit more equations are created to explain the faulty equations
because there isn't enough mater to explain movement and we add dark mater and dark energy and dark flow ignoring space itself the whole time
How do we know that space wasn't already here and mater and time was created by the negative energy of space and the space time distortion associated with mater is nothing more than surface tension.

 

[Whitewolf4869]

Don't be insulted I am just rattling some chains
If Einstein hadn't dropped out of high school and become a free thinker who knows where we would be with this right now

 

[alexg]

Don't be insulted I am just rattling some chains
If Einstein hadn't dropped out of high school and become a free thinker who knows where we would be with this right now

But he didn't. Where did you get the idea that he had?

He attended the Luitpold Gymnasium until he was 15, when his family left Germany.

He then attended the Aargau Cantonal School to complete his secondary schooling, and then the Swiss Federal Polytechnic in Zurich, where he got his degree.

 

[Drakkith]

#1 The theory is all wrong vacuums don't expand

A vacuum is an area of space devoid of matter. It cannot expand because it isn't "something". What is meant is that the geometry of space is set up in such a way that it causes two objects to get further apart as time goes on, yet neither of them are actually moving. This is very counterintuitive and there are many threads and posts dedicated to discussing it here on PF. A quick search or a look at the first few pages of the Cosmology forum will show a few.

#2 So comparing space to balloons or bread is foolish

No, assuming the bread or balloon analogy is actually the full description of the model is foolish. They are simply analogies developed to help people understand.

#3 Then an equation is created to explain what we see through our telescopes

All equations are created to explain a phenomena we observe or theorize. There is no other way to simplify our observations other than by developing equations to explain the underlying mechanisms for what we are observing. For example, if you wanted to explain what happens when someone throws a baseball, you could put together a monumental list with a verbal description of all possible throws and define a million different descriptions of how "hard" it is thrown, OR we can simplify the entire thing by using a simple mathematical equation and an explanation of how and when to use it. F=ma. This one equations let's us calculate almost any thrown ball.

#4 When that doesn't fit more equations are created to explain the faulty equations
because there isn't enough mater to explain movement and we add dark mater and dark energy and dark flow ignoring space itself the whole time

You are saying that we shouldn't attempt to explain phenomena because we don't have *all* the information? The we wouldn't be able to explain ANYTHING. It is not possible to have all knowledge of everything.

How do we know that space wasn't already here and mater and time was created by the negative energy of space and the space time distortion associated with mater is nothing more than surface tension.

You seem to be stringing a bunch of scientific words with no knowledge of what they actually mean or the context of where they are supposed to go. Current theories and models fully describe what we know and are backed up by large amounts of evidence for most of it. If you learned the theories you would know WHY we believe what we do.

Don't be insulted I am just rattling some chains

Who's chains are you rattling? Certainly not mine. The only thing you're doing is showing your ignorance of Cosmology and Science in general. I recommend not attempting to rattle anyone's chains until you know more about the subject under discussion. Continuing to post in this kind of attitude will only get you banned.

 

[GeorgeDishman]

Don't be insulted I am just rattling some chains ...

Nobody will feel insulted, all you are doing is publicising your ignorance of the subject. If you have an alternative explanation that works for cosmological redshift, the stretching of supernova light curves and the intensity of the CMBR that hasn't already been thought of and proven to be wrong, by all means lay it out.

 

[Whitewolf4869]

Your absolutely right and I am working on it.
It just seems to be that every time someone thinks outside the box there is always some one that has to protect there ego. I realize that a lot of people have spent many years studying and teaching this subject and my own (bizarre) notions are based on common theory but if we don't constantly question popular belief we are doomed to failure.

 

[Drakkith]

Your absolutely right and I am working on it.
It just seems to be that every time someone thinks outside the box there is always some one that has to protect there ego. I realize that a lot of people have spent many years studying and teaching this subject and my own (bizarre) notions are based on common theory but if we don't constantly question popular belief we are doomed to failure.

The problem is not that no one is thinking outside the box, or that people that are thinking outside the box are laughed at, it's that sooooo many people with only the vaguest idea of what the current theories say try to argue that they are wrong.

It would be like me arguing that Paton Manning or some other football star is the worst player ever just because I don't like him, I don't watch football and I saw 1 game where he did bad, or something similar.

My best piece of advice I can give you is to simply learn the theory. Learn why it is viewed as it is. Only then can you make an informed decision. This doesn't mean that you need to go to college for years and get into the math heavily, only that you look around at the various posts here on PF, sites on the internet, books available, and the countless other sources and get a good grasp on the basics. If you don't understand why something is viewed as it is, ASK. There are multiple people here willing to help you understand, and if they can't they can usually tell you where to find out.

 

[GeorgeDishman]

Your absolutely right and I am working on it.
It just seems to be that every time someone thinks outside the box there is always some one that has to protect there ego. ... if we don't constantly question popular belief we are doomed to failure.

There's nothing wrong with questioning the current model, people do that all the time, but when your question gets the answer that an aspect is based on some measurement, you have to then constrain your alternatives to also fit that observation. If the alternatives are ruled out, accept that part and move on. There are many areas where we simply don't have a model at all at the moment hence lots of scope for new ideas.

Look at what happened into Einstein's cosmological constant. Based on Hubble's observation at the end of the 1920's, he commented that it was his "biggest blunder", everyone asumed it had a value of zero, until 1998 when just a handful of measurements of distant supernovae overthrew seven decades of entrenched belief. People seem to think there is some establishment conspiracy to stifle new ideas but the opposite is actually the case, the groups that made those observations won the Nobel Prize for their discovery.

 

[Whitewolf4869]

Hears an alternative for you. Have you read any papers by William Tifft he and others found that c is not a constant.

 

[steve watson]

I'm coming in on the tail-end of this, so forgive me, but I am fascinated by the topic of your discussion.

I think that a fundamental problem regarding the question of whether space is expanding is the fact that we treat "space" as a "thing", "something", i.e., a planet, a dog, a grain of sand, an atom, etc., etc., etc., rather than "nothing", i.e., the absenceof "something".
If we viewed "space" as "nothing", theabsence of "something", which it must be, then "space", which is "nothing" cannot be expanding.

 

[Drakkith]

I'm coming in on the tail-end of this, so forgive me, but I am fascinated by the topic of your discussion.

I think that a fundamental problem regarding the question of whether space is expanding is the fact that we treat "space" as a "thing", "something", i.e., a planet, a dog, a grain of sand, an atom, etc., etc., etc., rather than "nothing", i.e., the absenceof "something".
If we viewed "space" as "nothing", theabsence of "something", which it must be, then "space", which is "nothing" cannot be expanding.

This is why understanding the context of the statement is important. When it is said that "space" is expanding, what is meant is that the geometry of space is set up in such a way that it causes objects to recede from each other at rate that increases with distance. Obviously trying to say that every time you want to talk about it is horribly inconvenient, so most people just say "Space is expanding".

 

[steve watson]

I know that understanding the context of a statement is of the utmost importance. And I said so when I posted my note. So my apologies again, I didn't mean to inconveience you. Still, first, words shouldn't be used so loosely. Words have meanings or they would be useless. And next, "space" not being "something" cannot cause "something" to happen. Who set "space" up? What does that mean? I"m not be sarcastic or cute, I am asking real questions and I am curious as to your answers.

 

[Drakkith]

I know that understanding the context of a statement is of the utmost importance. And I said so when I posted my note. So my apologies again, I didn't mean to inconveience you. Still, first, words shouldn't be used so loosely. Words have meanings or they would be useless. And next, "space" not being "something" cannot cause "something" to happen. Who set "space" up? What does that mean? I"m not be sarcastic or cute, I am asking real questions and I am curious as to your answers.

The problem is that while words may have specific meanings, the models themselves are NOT based on words. There is no word that describes the geometrical layout of a particular area of space. That requires math. So when you take the model and have to explain it verbally in english or other spoken language, it gets garbled and misunderstood.

What we mean when we talk about space is that when you set up objects in space and do certain things with them, they behave a certain way depending on how the underlying geometry is set up. Curvature of space is a good example. We often talk of an analogy of drawing a triangle on the surface of the Earth. If the surface were flat, all the angles would add up to 180 degrees. However, the Earth is a sphere and is curved. So as long as you make the triangle big enough to notice the curvature, you can measure the angles as adding up to MORE than 180 degrees.

Similarly space itself can be curved or be flat. Note that nothing anywhere describes what space "is". It only describes the way objects behave and interact. If I were to "draw" a huge triangle in space, and moved waaaay back and measure the angles and they added up to 198 degrees, then I would say that space is curved like a sphere. I'm not saying that space is made up of something, or anything about what space "is", I am only describing how my triangle and other objects behave.

 

[steve watson]

I understand, and I appreciate your response. These mathematical concepts trouble me. Math is trickey and can lead to strange and unverifiable notions and theories. My problem is with the nature of "space" and what it is or rather what it is not. Nobody seems to be able to give me a straight answer. But everyone seems to think "space" is a "thing" rather than "nothing". If "space" were "nothing" wouldn't that turn a lot of these theories upside down?

 

[Drakkith]

I understand, and I appreciate your response. These mathematical concepts trouble me. Math is trickey and can lead to strange and unverifiable notions and theories.

I don't think math is nearly as "tricky" as you think it is. The building blocks of any theory and model are mathematical formulas and equations that explain the way all the different pieces of the theory fit together. Many of these are simple equations that explain observed phenomena, while others are horribly complex to calculate, such as the Schrodinger equation in QM. Even so, the math itself must be shown to be correct and accurate.
Edit: Also, perhaps the most important thing, is that the theories themselves MUST be validated by observations and evidence. Without this a theory cannot be "accepted" fully. Hence why string theory is still not considered to be a mainstream accepted theory. It has no evidence beyond math.

My problem is with the nature of "space" and what it is or rather what it is not. Nobody seems to be able to give me a straight answer. But everyone seems to think "space" is a "thing" rather than "nothing". If "space" were "nothing" wouldn't that turn a lot of these theories upside down?

No, as no one is describing some underlying makeup of space itself. Any discussion about the shape of space, the geometry, or anything like that only describes how objects interact within it. Put simply, we don't know, and perhaps can't know, what space "is", if it is anything at all.

 

[steve watson]

Well you're way out of my league regarding math and the mathematical theories you speak of, but when you descirbe "space" as having a "shape", aren't the only things that have a "shape" things that exist? And if "space" has a "shape" doesn't that mean "space is a "thiing"?

 

[Drakkith]

Well you're way out of my league regarding math and the mathematical theories you speak of, but when you descirbe "space" as having a "shape", aren't the only things that have a "shape" things that exist? And if "space" has a "shape" doesn't that mean "space is a "thiing"?

Define "thing".

 

[steve watson]

anythat that exists: a planet, an atom, a needle, a haystack, a grain of sand, everythig except nothing, i.e., the lack of something. ...

 

[Drakkith]

anythat that exists: a planet, an atom, a needle, a haystack, a grain of sand, everythig except nothing, i.e., the lack of something. ...

All those are capable of being observed, measured, and interacted with. They follow certain rules and feel certain forces. Does space do this? Can we observe "space itself"? In my opinion the only force that space obeys is gravity. Except that gravity is a result of the curvature of space due to mass, not a "real" force. So maybe we can say that space is altered by mass. Does this count as observing space?

I don't know the answer, and many people have many different opinions on what space is. The simple answer is that we don't know. However the current theory that explains the behavior of the universe on the largest scales is General Relativity. In the context of GR space has geometrical structure that determine how objects interact. It says nothing about what space "really is".

So, when someone talks about space expanding, realize that within the context of the theory and model that we use to describe the universe, we only mean that two objects, far enough apart so that gravity is very weak between them, will recede from each other due to the geometric structure of spacetime. Whether space is being created, being stretched, or something else is up for debate and is merely an interpretation.

 

[steve watson]

Not sure, but at a mininimum, I think it counts as observing the relationship between "things", and, by implication, but to a much lesser degree, "space" itself. But i don't think there is much to reveal about space itself since it is "nothing"., i.e., there is nothign to reveal. On the other hand, I think it is of the utmost importance to understand the relationship between "things" and "space".

Most interesting, as I was under the impression that scientist today generally believed that space was something because howelse could it be curved. Nothing cannot be curved as there is nothing to be curved.

I understand, but doesn't the "big bang" theory (which i don't subscribe to) and other theories setting out the beginning of time proclaim "space" to be a "thing" .. and if it is a "thing" where does it end, when does it end (if this is even a sensical question when it comes to matter, i.e., "things" and if things have no end, i.e., infinite, then how come you can identify one thing from another thing?

 

[Drakkith]

I understand, but doesn't the "big bang" theory (which i don't subscribe to) and other theories setting out the beginning of time proclaim "space" to be a "thing" .. and if it is a "thing" where does it end, when does it end (if this is even a sensical question when it comes to matter, i.e., "things" and if things have no end, i.e., infinite, then how come you can identify one thing from another thing?

The Big Bang theory doesn't set out the beginning of time. It merely says that the universe was once in a hot, dense state and expanded from there, cooling off in the process as the density dropped. It is supported by what most would consider overwhelming evidence.

And I'm not sure what you are getting at about infinite. The universe may or may not be infinite, we do not know. If it is infinite in size that has no bearing on what space is as far as I know.

 

[GeorgeDishman]

Hears an alternative for you. Have you read any papers by William Tifft he and others found that c is not a constant.

I haven't but that's a good example. Here's his bio in Wikipedia:

http://en.wikipedia.org/wiki/William_G._Tifft

It discusses his involvement with the idea of quantised redshift but not variable c. Note that that work was about 35 years ago, before the Hubble and other space telescopes. It became apparent that redshift isn't quantised some years after that but the acoustic resonances in the early universe means there is a tendency for the clumping of matter to shows peaks which, with limited data, could look like quantisation.

Regarding variations in c, that is closely related to the fine structure constant. Observation of some variation in that was reported some years ago (2004) by a group using a telescope in the southern hemisphere and they concluded it might have changed over time. Their result was that it was smaller by 5 parts per million (ppm) 10 billion years ago (z~1.8).

In response to peer questions, they recently extended their observations in the northern hemisphere and found a similar degree of variation but in the opposite sense. Using a different telescope in the northern hemisphere, they find it was about 7 ppm higher 10 billion years ago.

Overall, the average change from that period is now 0.6ppm with an accuracy of ±1.6ppm which means the most likely conclusion is no change. They have had to change their hypothesis to now suggest there is no time-related variation but possibly a variation with position. On the other hand, since nearly all the results from one telescope are low while those from the other are high, it seems much more likely to be a problem of calibration.

The point of this is that measurements in 2004 might have agreed with Tifft's suggestion, though at a very low level, but the same measurements made by the same team using a second telescope and published in 2011 have eliminated that apparent trend. Observations are improving all the time and papers written just a few years ago may well be out of date.

This is the paper in question:

http://arxiv.org/abs/1008.3907

That's an excellent example of how things that can appear to be taken for granted are actually being questioned all the time.

 

[GeorgeDishman]

My problem is with the nature of "space" and what it is or rather what it is not. Nobody seems to be able to give me a straight answer. But everyone seems to think "space" is a "thing" rather than "nothing". If "space" were "nothing" wouldn't that turn a lot of these theories upside down?

It's not a trivial question. For example, if space is the absence of anything, how can it have a permitivity and permeability? What about the Casimir Effect, is that caused by "stuff in space" or is it a property of the vacuum itself? Space may not be a "thing" but it definitely seems to have measurable properties. You might also like to do a search for the term "substantivalism" (be careful with the spelling) and look at the Hole Argument just to get a flavour of this topic:

http://plato.stanford.edu/entries/spacetime-holearg/

Note that the Hole Argument is a problem for manifold substantivalism but perhaps not for metric substantivalism (which the SEP barely mentions).

You should also consider what gravitational waves (as indirectly measured by Hulse and Taylor) and "gravitational wave recoil" imply for the existence of the metric.

http://www.black-holes.org/explore2.html

 

[steve watson]

No, it's not a trivial question .. tks for your response and the website info .. it's not easy to understand ...

 

[Orion1]

Cosmology scale factor equation:
\frac{\lambda_0}{\lambda_t} = \frac{T_t}{T_0} = \frac{a(t_0)}{a(t)} = 1 + z
λCDM redshift at decoupling:
z = 1090.89
CMBR temperature at present:
T_0 = 2.72548 \; \text{K}
T_t = T_0 (1 + z) = 2.72548 \; \text{K} \times (1 + 1090.89) = 2975.92 \; \text{K}
Universe temperature at photon decoupling time t:
\boxed{T_t = 2975.92 \; \text{K}}

However, does the Cosmology scale factor equation also work this way?

Universe total observable radius:
R_u(t_0) = 4.399 \cdot 10^{26} \; \text{m}
\frac{R_u(t_0)}{R_u(t)} = \frac{a(t_0)}{a(t)} = \frac{T_t}{T_0} = 1 + z
\boxed{a(t_0) = 1}
R_u(t) = a(t) R_u(t_0) = 9.158 \cdot 10^{-4} \times 4.399 \cdot 10^{26} \; \text{m} = 4.028 \cdot 10^{23} \; \text{m}
Universe total observable radius at photon decoupling time t:
\boxed{R_u(t) = 4.028 \cdot 10^{23} \; \text{m}}
[/Color]
Reference:
Total amount of energy in the Universe - Orion1 #13
Lambda-CDM model - Parameters - Wikipedia
Scale_factor - Cosmology - Wikipedia
Redshift formulae - Wikipedia
Cosmic microwave background radiation - Features - Wikipedia
Recombination - Cosmology - Wikipedia
Timeline of the Big Bang - Photon epoch

 

[GeorgeDishman]

However, does the Cosmology scale factor equation also work this way?

Universe total observable radius:
\frac{R_u(t_0)}{R_u(t)} = \frac{a(t_0)}{a(t)} = 1 + z
\boxed{a(t_0) = 1}

Yes, in fact that is the definition of a(t). However, that only gives you the ratio of the present size to that at the time of emission. The values you quote of roughly 42 million and 46 billion light years respectively are correct but to get those, you need to find the lookback time first.

 

[Orion1]

Cosmology scale factor equation:
\frac{R_u(t_0)}{R_u(t)} = \frac{a(t_0)}{a(t)} = \frac{T_t}{T_0} = 1 + z

Universe total observable radius:
R_u(t_0) = 4.399 \cdot 10^{26} \; \text{m}

Cosmic neutrino background radiation temperature at present:
T_0 = 1.95 \; \text{K}

Cosmic neutrino background radiation temperature at neutrino decoupling time t:
T_t = 1 \cdot 10^{10} \; \text{K}

R_u(t) = R_u(t_0) \left( \frac{T_0}{T_t} \right) = 4.399 \cdot 10^{26} \; \text{m} \times \left( \frac{1.95 \; \text{K}}{1 \cdot 10^{10} \; \text{K}} \right) = 8.578 \cdot 10^{16} \; \text{m}

Universe total observable radius at neutrino decoupling time t:
\boxed{R_u(t) = 8.578 \cdot 10^{16} \; \text{m}}
[/Color]
Reference:
Total amount of energy in the Universe - Orion1 #13
Timeline of the Big Bang - Hadron epoch - Wikipedia
Neutrino_decoupling - Wikipedia
Cosmic neutrino background - Wikipedia
Red shift - Highest redshifts

 

[GeorgeDishman]

Universe total observable radius:
R_u(t_0) = 4.399 \cdot 10^{26} \; \text{m}[/Color]

That figure is for what is observable optically, i.e. the CMBR. We can't observe primordial neutrinos. However, your end result will still be a reasonable rough estimate.

 

[dtyarbrough]

The rate of expansion (hubble constant) of the universe is equivalent to the sun moving 3/4 of a mile farther away in 100 years. Do the math. The solar wind adds solar particles to the solar system and universe. This causes distant objects to appear ever more distant as space becomes more opague. Space is not empty as recent articles have stated.

 

[GeorgeDishman]

This causes distant objects to appear ever more distant as space becomes more opague.

That makes no sense, you need to explain why space becoming opaque would change the wavelength of a spectral line.

 

[Mark M]

The rate of expansion (hubble constant) of the universe is equivalent to the sun moving 3/4 of a mile farther away in 100 years. Do the math. The solar wind adds solar particles to the solar system and universe. This causes distant objects to appear ever more distant as space becomes more opague. Space is not empty as recent articles have stated.

This is so wrong, I have to question if you have a clue about what you're talking about.

First of all, recessional velocity on large scales requires a frame of reference. The distance from this FoR is then multiplied by a scale factor, Hubble's constant. This is shown by Hubble's law:

V=H_{0}D

Also, expansion only effects very large objects, such as galaxies or super clusters, not the Sun.

Second, Hubble's constant is estimated by WMAP to be 70.8 ± 1.6 (km/s)/Mpc.

So, an object that is very far away will appear to have an extremely high recessional velocity, your calculation was completely made up, and had no basis whatsoever.

Also, the cosmic microwave background provides conclusive evidence the universe is expanding and cooling.

 

[GeorgeDishman]

This is so wrong, I have to question if you have a clue about what you're talking about.

He doesn't, he is confusing reddening with redshift.

.. Hubble's law:

V=H_{0}D

Use 1AU for D to get V then multiply by a century and you might get the figure he quoted. Of course that ignores all orbital mechanics and doesn't seem to have any rational connection to the solar wind anyway.