Unit of Measurement: Arbitrary or Dependent on Physical Laws?

[Rafterman1]

Just a thought I literally just came up with sitting here on a Sunday morning after having joined this site about a minute ago (first timer). Reading some of these posts about the expanding universe and thinking about the idea of relative positions, I thought of this angle on things. Now, this has probably already been thought up but I haven't got my copy of 'science theories' handy.
Here it is; what if the universe does not expand, but matter condenses. This does not indicate whether space is expanding/fixed or anything, but just that matter is condensing. This could explain the observation that points in space are moving away from one another, as the distance between galaxies etc. would increase as the size of the galaxies decreases. The red shift observation indicating that areas farther from the 'centre' of the universe are moving faster away could be explained (perhaps) by faster rates of condensation due to less energy being present the further you move from the 'centre'.
Now, it is also my understanding, and this is where the relativity part comes in, that this condensation of matter would not be directly measurable. This is because the instruments, and indeed the observer, as well as the observed object(s) would all be condensing at approximately the same rate. Similar to the experiment where an observer is in a windowless room with no references other than himself or the walls. Are the room and observer moving at a constant velocity in a straight line, or are they stationary? Ok, so this is completely different situation, but the point is that no measuring device can observe what is trying to be measured, because the device is experiencing the same change. Therefore we cannot measure the condensation of matter on a small scale, but can see the change in distance between objects when talking about galaxies etc. What about planets and stars, why don't they contract in relation to one another? Measuring change in distance between them on this scale would not be noticeable, partly due to the small distances, and partly due to gravity keeping the masses at fixed orbits or at least causing them to coalesce into clusters.
So there it is. Please feel free to shoot this one out of the sky if you wish, as I don't think it to be the case anyway, I think I just had one too many coffees. Just food for thought...

 

[dx]

Imagine 2 circles a distance d apart. If the circles get smaller, the distance between their centers wont.

 

[Rafterman1]

Alright, good point there, but still, if you were in one of those circles observing the other, it would appear to be moving away from you...

 

[Mentz114]

Rafterman1, welcome to PF.

This idea of condensation vs expansion has been proposed and it may well be possible to make one that explains observations.

I'd like to point out that the universe does not have a centre. It is like the surface of a sphere, which does not have any point you could a centre. Our models of the cosmos are framed in 4 dimensions, so the 'surface' is a 3D hypersurface. Hard to imagine.

Each observer in this universe sees matter receeding ( or at least redshifted according to distance) and in that sense is at the centre of their own observable universe.

 

[Rafterman1]

Thank you Mentz, yes I understand there is no true 'centre' in the classic sense. I guess what I am trying to say is that given that we can only say something is true if we can observe this (directly or indirectly). And I am, in a way, trying to play the devil's advocate here by highlighting a possible other explanation for the handful of observations that relate to the state of our universe. Could our current observations also be explained by the condensation of matter? Or is there any evidence relating to the state of the universe that refutes this?

 

[Mentz114]

Rather than explanations we have theories, which are in effect mathematical models. General relativity based cosmological models actually predict an expanding space-time, which seems to fit the facts, so why look for something else ? If all observations were explained by a consistent theory of 'condensation', we would then have to choose which one we believe. But such a theory does not exist, and there seems to be little point in looking for one.

 

[Dale]

Imagine 2 circles a distance d apart. If the circles get smaller, the distance between their centers wont.

The distance will get "smaller" if the unit of measurement is based on, r, the radius of the circles. In such a system of measurement there would be no way to tell if d or r is changing, all you can really know is that the ratio d/r is changing.

 

[yuiop]

Imagine 2 circles a distance d apart. If the circles get smaller, the distance between their centers wont.

If the circles were solid objects then presumbly rod and rulers would be shrinking to the same extent and the measurement of the distance from the centre of one circle to the other would be longer using those contracted rulers.

Of course clocks would have to speed up by the same factor (or light would have to slow down) so that measurements made by sending light signals were consistent with measurements made by rulers and things start getting complicated when you try extending the idea to a more complicated dynamic universe.

 

[Ich]

There is no way to distinguish both scenarios by observation, so you can say that both viewpoints lead to the same predictions. But there is an important philosophical difference: Both predict that we observe an expanding universe, but one theory explains this observation by an expanding universe, while the other postulates an unobservable static universe and an unobservable shrinking of rulers etc. Economy of thinking dictates that we eliminate all unobservable quantities from our theories if reality can be described equally well without these.

 

[shalayka]

One other comment regarding dx's thoughts:

If the surfaces are retreating toward their centres, then the photons they emit will be redshifted, since the point of emission at the beginning would not equal the point of emission at the end (assuming photon emission is not instantaneous). Likewise, if the surfaces were moving away from the centres, the photons would be blueshifted. Of course, this idea goes a little haywire when the surface is moving away from the centre at a velocity greater than c (would this lead to negative wavelength? heh).

I have to admit though, I still believe wholeheartedly in the metric expansion of space (and dark energy if need be).

 

[TR345]

This was discussed before here, and I thought it was kind of interesting.

https://www.physicsforums.com/showthread.php?t=220284

someone argued that we would see blue shifting instead of red shifting if this was the case.

 

[sLeeping_bEauti]

If the circles were solid objects then presumbly rod and rulers would be shrinking to the same extent and the measurement of the distance from the centre of one circle to the other would be longer using those contracted rulers.

Of course clocks would have to speed up by the same factor (or light would have to slow down) so that measurements made by sending light signals were consistent with measurements made by rulers and things start getting complicated when you try extending the idea to a more complicated dynamic universe.

I was just wondering when you say time would have to speed up what do you mean? What is time relevant to?
And it depends on whether you believe the universe is open or closed...the rods and rulers would shrink if the universe is closed but if it was open wouldn't they stay the same but objects would just get smaller.
Or if you take that a contracting universe is returning to its original state (before the big bang) then the space between the objects wouldn't have any effect as they would all stop at a centre.
If that makes sense to any of you.
x

 

[sLeeping_bEauti]

Also to what Shalayka said...
as we are still seeing red shift i don't think what i said about the universe returning to its original state is possible because it would have a blue shift so yea scratch what i wrote about that :)
x

 

[Blueprint]

Whats the explanation as to why the universe just happens to be expanding at just below the critical rate?

 

[sLeeping_bEauti]

Whats the explanation as to why the universe just happens to be expanding at just below the critical rate?

What do you mean?
all i can think is that probably because no one knows what the critical rate is and it hasnt become critical yet.

 

[marrsal]

condensation rather than expansion

And I am, in a way, trying to play the devil's advocate here by highlighting a possible other explanation for the handful of observations that relate to the state of our universe. Could our current observations also be explained by the condensation of matter? Or is there any evidence relating to the state of the universe that refutes this?[/QUOTE]

I am glad to know I am not the only one who has this idea. There are few details you did not mention in your post. I am not sure where can I read about the condesation theory rather than the expansion one. I do not understand why we keep avoiding the obvious. Centuries ago, we though that the Earth was flat (knowing that everything in the sky was spheric). Same now, we all see that life of stars and galaxies is created based on condensation/exlosion cycles. Why not to accept the idea that the hole universe are, as you said, a huge space filled with areas of condensation/explosion of matter. The detail I would have to add is that the limits between these clusters of matter is filled with its own escence at rest and therefore suspended in time (no time).

Kudos for the expansion/condensation theory!

Manuel.

 

[TR345]

What would be interesting is if the "contracting" theory could link with GR especially time dilation.

 

[MiltMeyers]

Great Idea. One thing is there is no center of our 4d bottle and one would have to use 4d logic to think about contracting. So it would be a big bottle and it is contracting. I have enough trouble understanding how there is no outside to the universe and no time before zero. One thing is if space was contracting then you could turn this around and say spce is shrinking faster now than in the past. With exspantion of space as each amount of space is added to the universe expands faster as the amount of space expands like compound interest. Space is what is exspanding isn't it not matter? I'm new to the forum and just have used my head and a book on relativity I read many years ago and what I pick up on TV. So if I have and bad idea let me know.

milt

 

[Libmr2bs]

I'm interested in a similar scenario except that it relates to a red shift due to gravitational attraction.

When considering the speed of objects revolving around a galactic boundary and the gravitational confluence at the center of the galaxy, it would appear that all luminous objects would be spiraling toward the center. If an object is spiraling toward that center, then it would appear that light from these objects would experience a red shift as the object would have a relative motion away from any external static frame. What is interesting is that the motion toward the center would cause a red shift from any observable direction except parallel to the axis of rotation. Additionally the observer's field of vision would encompass a larger field of red shift on the near side of the galaxy and the blue shift would encompass a larger field on the far side of the galaxy. The farther away a galaxy the more this shift would be observable.

 

[MiltMeyers]

That is a hard thought to think about and I find the idea that space is exspanding and when we look out to another galaxy we see it in the past and when the universe was smaller that is about as far as I can stretch my mind. This of course means that there is a curve in a beam of light as it travels from galaxy to my eye and that is in the 4th demension. This curve will bring one back to were it started from that is if you could go instantly around the loop and you should the way I have it figured out pass through the singularity or were it was any way.So back to topic I fail to see the way the details would work if the universe was contracting and I'm leaving that discussion to wiser chaps than me.

 

[Chronos]

I agree with Milt, show the theory and evidence before casting aside the current model [LCDM].

 

[thenewmans]

First I'll poke holes: The expansion does not occur evenly everywhere. It's mostly between galaxies. Matter (or gravity) keeps it from happening as much in galaxies. How can that be explained by condensation? (This is something I've been thinking about casually for years.)

 

[thenewmans]

Now I'll compliment: Even if the difference is indistinguishable and untestable, this concept could open the door to other ideas. Einstein realized that acceleration and gravity are indistinguishable in the right conditions. That led to GR. He realized that it's not light speed that changes but time and distance. Maybe this idea will lead to dropping a tensor from GR.

 

[MiltMeyers]

If you want to play with the condensation idea I would think that in the beginning the singularity would have been everywere and then space and time started to collapse. As space and time collapsed it would have gone larger to smaller and space time would have a negative curve as I see it. There would be a mixing zone in the galaxies and gravity would have to repel to keep from collapsing with space time. The answer is I like the current model and I'll stand pat. But my mind is open. Dropping a tensor from GR, wow, can we do that or will someone roll over in their grave?

 

[MiltMeyers]

Yes GR should work either way. Also the mixing zone in the Galaxys if we were collapsing would add to gravity and help with dark matter. It's effect would show up at low levels of gravity like dark matter does. What is your opinion on that?

milt

 

[NYSportsguy]

Matter and radiation are gravitationally attractive, so in a maximally symmetric spacetime filled with matter, the gravitational force will inevitably cause any lumpiness in the matter to grow and condense. That's how hydrogen gas turned into galaxies and stars. But vacuum energy comes with a high vacuum pressure, and that high vacuum pressure resists gravitational collapse as a kind of repulsive gravitational force. The pressure of the vacuum energy flattens out the lumpiness, and makes space get flatter, not lumpier, as it expands.

 

[MiltMeyers]

NYSportsguy Thanks for your thoughts. The vacuum(space time) temp is even all over due to inflation, at least I would put that forward. I see the difference in matter and energy and space time. I always thought of space time to be the same all over and that is an interesting thought that the pressure of the zero point energy smoothing out the lumpness. Maybe that will explain why the CBR can be 10% higher one hemosphere than the other and space time seems to be the same temp. I think it will really be interesting to see what will be the outcome of looking at lower and higher frequencys and can see how the CBR evolved?

Now that said if two bodies were moved apart in a galaxy and the force between them is measured we are told it will drop to a low point but will not drop to zero. In a collapsing universe the space time would try to push them together and would help explain the fact gravity goes on and on at higher level than math allows. In an exspanding universe there is a mystery as to how to explain dark matter.

Thenewmans. When I was in school I tried to prove that the Earth was exspanding and we were also exspanding to give one G. (the Earth exspanse to meet the motionless apple)The problem is a lead ball has more gravity to it than a ball of feathers.
I don't know what that means but I just threw it in.

 

[NYSportsguy]

Thenewmans. When I was in school I tried to prove that the Earth was exspanding and we were also exspanding to give one G. (the Earth exspanse to meet the motionless apple)The problem is a lead ball has more gravity to it than a ball of feathers.
I don't know what that means but I just threw it in.

\

How gravity works on all objects is that it exerts dirfferet amounts of its force or "pull" depending on the mass of the object it is working with. EX: If you take a rock and drop it form a cliff gravity will act with a specific amount of force to bring that rock down. Now if you break that rock apart into say 5 pieces, and drop all 5 pieces, gravity will change the amount of force it acts on each piece of rock exerted and bring it down so that acceleration remains constant for all pieces at 9.8 m/s^2 here on earth. It osmehow regulates itself.

 

[jonmtkisco]

Hi MiltMeyers and NYSportsguy, here's an easy way to think about why the pull of gravity corresponds to the mass of the object:

Any massive test body is comprised of atoms, and the vast majority of the mass of atoms is comprised of hadrons (protons and neutrons). So to simplify this discussion I'll just ignore the mass of electrons and assume that all hadrons have the same mass. When a "force" such as gravity acts on a hadron, Newton tells us that F=Ma, so any given force potential causes a single hadron of mass=1 (in a hadron-based mass scale) to accelerate toward the source at a specified acceleration rate (let's say a=1 in our scale). The hadron's inertia is what resists the force of gravity and it is what that force must overcome in order to accelerate an M=1 hadron at a=1. If our test particle contains 1M hadrons, then the same force of gravity as before will separately and equally pull on each hadron, causing each hadron to accelerate at a=1 and, indirectly, causing the test particle as a whole to accelerate at a=1. Gravity is an inexhaustible source of force, in the sense that it can pull on an unlimited number of hadrons at once (subject to physical space limitations) without diminishing the force it applies to each individual hadron.

By this elementary reasoning it would defy common sense to expect a more massive object to accelerate faster than a less massive object. Linking individual hadrons together (chemically) does not cause any (significant) change in their individual inertias. It would be bizarre indeed if linking hadrons together caused them to each become more (or less) susceptible to gravitational force than the same number of hadrons that are unlinked.

Jon

 

[junglist]

By this elementary reasoning it would defy common sense to expect a more massive object to accelerate faster than a less massive object. Linking individual hadrons together (chemically) does not cause any (significant) change in their individual inertias. It would be bizarre indeed if linking hadrons together caused them to each become more (or less) susceptible to gravitational force than the same number of hadrons that are unlinked.

Jon

great post!

 

[MiltMeyers]

Great posts! Yes I am in error and thanks for nailing my foot to the floor. Mass will we find the higgs boson? I always liked the idea that the universe and the object are connected and when you have inertia you move the universe. Maybe the universe and the object trade higgs particles?

Back to gravity being due to warped space time(ST). Space time is warped or curved by an exspansion of ST and that would mix with mass warped ST and show up at low levels. So in an exspanding universe the curve would lower gravity but with an collapsing universe it would add to gravity, or do I have that turned around.

Junglist I agree there are some really smart people reading this forum.

 

[NYSportsguy]

Hi MiltMeyers and NYSportsguy, here's an easy way to think about why the pull of gravity corresponds to the mass of the object:

By this elementary reasoning it would defy common sense to expect a more massive object to accelerate faster than a less massive object. Linking individual hadrons together (chemically) does not cause any (significant) change in their individual inertias. It would be bizarre indeed if linking hadrons together caused them to each become more (or less) susceptible to gravitational force than the same number of hadrons that are unlinked.

Jon

JonMTKisco - That exactly what I said in my explanation above. It's the force that varies with variation in the masses being "pulled" on...the acceleration stays constant. I already know that but thanks for the more "Quantum" explanation.

 

[NYSportsguy]

The original statement to start this post was: "What if the universe does not expand, but matter condenses. This does not indicate whether space is expanding/fixed or anything, but just that matter is condensing. This could explain the observation that points in space are moving away from one another, as the distance between galaxies etc. would increase as the size of the galaxies decreases."

To Answer that my Reply Would Be: If matter were condensing it would still be the same amount of matter however volume would shrink. Since density = mass/volume all we would need to do it measure our own galaxy's density at a certain point in time and then say 500-1000 years later measure the density again. If we see it is increasing, we can say that it is because the volume has been decreasing due to the "condensing process" of matter and as a result the contraction theory would be correct.

However I don't believe scientists have found the density of individual galaxies to be increasing as time passes so there goes that theory.

 

[MiltMeyers]

NYsportsguy----Thats a good point about the fact the galaxys would decrease. I think the spin of the galaxy would hold the stars out in an orbit about the center but as you say the push would be to collapse the galaxy. That is why I said that the push would help gravity and the stars would spin as if there was dark matter out there holding the galaxy together. No I'll stick to what I understand and that is an exspanding universe.

 

[robheus]

I think this "dilemma" is just the ordinary issue of how to define a ruler. And that is just basic sanity, applicable anywhere, that your choice of ruler does not change anything. All physics stays the same (only the numbers/outcomes of your formula's change).
And if I'm not wrong, even a time dependent unit would not make a difference.

It is analogous to the choice of frame of reference.

So the whole issue is one which is solely based on choice of ruler, and there is no physics that change, so not testable by definition.

And same as that we choose for our frame of reference not the galactic center or andromeda but (for practical reasons) the solar system or earth, likewise we do not choose our length unit to be the distance between too far away galaxies, but some more practical unit.