Is an exapnding universe a violation of the principle of relativity?

[quantumtopology]

Moderation Note: The following 5 posts have been moved from Redshift z in favor of having their own topic here.

 

Hi, guys

 

Is this a real paradox or only apparent:

If one believes in a expanding universe that is also isotropic, one is forced to think that the universe provides us with a preferred velocity at our particular location. Why is this? If we were moving at a sufficiently higher velocity than the current one from this position, we should not get such isotropy because in front we would see less redshift for a given brightness and behind us much more. So here we have what seems a conflict between cosmology and the Principle of relativity from which so many things are deduced in modern physics, that tells us that there is not preferred velocity as far as laboratory physics goes, but if expansion really exists, the universe is giving us a preferred velocity, a kind of absolute velocity.

 

What do you think?

This paradox was formulated many years ago, now we have an added factor (the apparently accelerated expansion) but I don't think it changes the reasoning.

 

Regards

Happy 4th of july

 

QTop

[modest]

It's a great question. The frame in which everything is 'at rest' is the frame in which all clocks agree on the age of the universe. It is the frame that keeps 'cosmic time'. The frame is not absolute in a non-relativistic sense. It's really just the most convenient frame to use.

 

The question that may be raised in philosophical cosmology is whether or not this cosmic time constitutes an “absolute time” in the sense that Einstein rejected in his special theory of relativity. “Absolute time” and “relative time” may be defined in terms of the relation of simultaneity. If time is absolute, then this relation is two-termed, and is expressed by sentences of the form “x is simultaneous with y.” If time is relative, then the simultaneity relation is three-termed and is expressed by “x is simultaneous with y relative to z,” where z is the reference frame relative to which x and y are simultaneous. This suggests that the cosmic time posited by big bang cosmology is not absolute time, since the time measurements are made relative to the privileged reference frame. For example, the assertion that the age of the universe is about [13.7] billion years old is elliptical for the statement “relative to the privileged reference frame, the universe is [13.7] billion years old.”

 

Encyclopedia of time by Samuel L. Macey p.145

 

~modest

[quantumtopology]

It's a great question. The frame in which everything is 'at rest' is the frame in which all clocks agree on the age of the universe. It is the frame that keeps 'cosmic time'. The frame is not absolute in a non-relativistic sense. It's really just the most convenient frame to use.

 

Very appropriate quote, thanks.

I have heard similar explanations, and I see what you mean, that nag me with this reasoning are: first that is more of a philosophical argument in the sense that it doen't really address the paradox but it talks about convenience, that reminds me of the classical vindication of the Euclidean geometry as the only one possible, that was later changed for the argument of the most convenient when it was proved that it was not the only one.

 

And secondly, the answer tipically tries to change the absolute velocity statement for the "preferred frame of reference" or the "privileged frame" but this doesn't agree very well with another principle that is constantly alluded to, the Copernican principle that rejects that we are in any privileged frame just because of the fact that it is our frame. So the fact remains that if one asks why would be this frame privileged the answer is always: because it's our frame, and that seems to be also the reason why it is the most convenient, apart from the fact that indeed is the most convenient for the expanding hypothesis.

 

So if we say that this velocity that the expansion of the universe provides us with is not absolute, we have to respond with respect to what is relative then, but our only answer seems to be that with respect to the rest of the cosmic objects of the universe, and that seems unsatisfactory .

 

Regards

QTop

[modest]

Very appropriate quote, thanks.

I have heard similar explanations, and I see what you mean, that nag me with this reasoning are: first that is more of a philosophical argument in the sense that it doen't really address the paradox but it talks about convenience, that reminds me of the classical vindication of the Euclidean geometry as the only one possible, that was later changed for the argument of the most convenient when it was proved that it was not the only one.

 

But, the objection 'things should be relative and this doesn't seem to be' is philosophical. It wouldn't be surprising if the rebuttal is equally philosophical.

 

And secondly, the answer tipically tries to change the absolute velocity statement for the "preferred frame of reference" or the "privileged frame" but this doesn't agree very well with another principle that is constantly alluded to, the Copernican principle that rejects that we are in any privileged frame just because of the fact that it is our frame. So the fact remains that if one asks why would be this frame privileged the answer is always: because it's our frame, and that seems to be also the reason why it is the most convenient, apart from the fact that indeed is the most convenient for the expanding hypothesis.

 

Relativity doesn't demand that every observer see the same thing. The previous quote puts it very well in that relativity demands a "relative to" component in a statement describing a situation. For example, velocity is relative so relativity would deny this statement "x has a velocity" but rather demand the statement read "x has velocity relative to y".

 

Likewise simultaneity is relative so a statement (to be completely accurate) must read "these two events are simultaneous relative to y".

 

So, let's dissect the paradox. An observer, A, in the hubble frame sees the universe isotropically. An observer, B, with a velocity relative to the hubble frame does not see the universe isotropically. If velocity is relative in this situation then it would not make complete sense to say "B has a velocity but A does not". We would rather need to say "B has a velocity relative to most of the mass of the universe (or, to be more correct: "relative to the hubble flow") while A does not". Likewise, most of the mass of the universe has a velocity relative to B.

 

The situation preserves the principle of relativity because the laws of physics are indeed relative in this situation. B does not "have a velocity". B has a velocity relative to something and that something has a velocity relative to B. Either person, A or B, can use the physics of relativity with the assumption that they, themselves, are at rest. And the physics will work for both. Neither observer has to assume that they are in an absolute state of velocity.

 

The Hubble flow's frame of reference is privileged only in the sense that most of the mass of the universe is in or very nearly in that frame. That is not a violation of the principle of relativity, it is just the physical situation. Only if the physics demanded that we use that frame would it be a violation of the principle. But, GR does not demand that. We solve the physics in that frame only because it is most convenient.

 

~modest

[quantumtopology]

But, the objection 'things should be relative and this doesn't seem to be' is philosophical. It wouldn't be surprising if the rebuttal is equally philosophical.

Only I'm not sure the objection is just philosophical or it has some scientifically empirical content too.

 

 

Relativity doesn't demand that every observer see the same thing. The previous quote puts it very well in that relativity demands a "relative to" component in a statement describing a situation. For example, velocity is relative so relativity would deny this statement "x has a velocity" but rather demand the statement read "x has velocity relative to y".

 

Likewise simultaneity is relative so a statement (to be completely accurate) must read "these two events are simultaneous relative to y".

 

So, let's dissect the paradox. An observer, A, in the hubble frame sees the universe isotropically. An observer, B, with a velocity relative to the hubble frame does not see the universe isotropically. If velocity is relative in this situation then it would not make complete sense to say "B has a velocity but A does not". We would rather need to say "B has a velocity relative to most of the mass of the universe (or, to be more correct: "relative to the hubble flow") while A does not". Likewise, most of the mass of the universe has a velocity relative to B.

 

The situation preserves the principle of relativity because the laws of physics are indeed relative in this situation. B does not "have a velocity". B has a velocity relative to something and that something has a velocity relative to B. Either person, A or B, can use the physics of relativity with the assumption that they, themselves, are at rest. And the physics will work for both. Neither observer has to assume that they are in an absolute state of velocity.

 

The Hubble flow's frame of reference is privileged only in the sense that most of the mass of the universe is in or very nearly in that frame. That is not a violation of the principle of relativity, it is just the physical situation. Only if the physics demanded that we use that frame would it be a violation of the principle. But, GR does not demand that. We solve the physics in that frame only because it is most convenient.

 

Nice reasoning.

Just one detail. Observer B is watching a very different universe than observer A, he would'nt be able to come up with an FRW metric or an expanding universe hypothesis. I don't know if this is in conflict with the general or special principles of relativity.

 

Regards

QTop

[modest]

Only I'm not sure the objection is just philosophical or it has some scientifically empirical content too.

 

I'd hope most philosophy has some scientific content. I don't see it as bad that an objection be philosophical. If a theory didn't follow Mach's principle, for example, that would be a philosophical problem (or, could be seen as one), but that would not necessarily make the theory scientifically invalid.

 

We can make an argument that the universe should follow Mach's principle or should follow the principle of relativity, but that would be a philosophical argument. And those are good and useful arguments. A lot of general relativity was inspired by the philosophy of Ernst Mach.

 

Nice reasoning.

Just one detail. Observer B is watching a very different universe than observer A

 

Well—no—he's seeing the same universe from a different perspective. That is as it should be because he is literally in a different perspective. The principle of relativity does not insist on everyone seeing the same thing. The CMB, for example, doesn't need to look the same to every observer. The principle would not require that.

 

It requires only that the laws of physics are the same for the two observers, or in the frame of reference of either observer.

 

, he would'nt be able to come up with an FRW metric or an expanding universe hypothesis.

 

He could come up with FLRW and an expanding universe, he just would not be stationary in the metric. He therefore wouldn't use FLRW to describe himself as an observer at rest. If he wanted to consider himself at rest, and he would need to be able to do that for the principle to be upheld, then he would solve GR for his own particular situation—that situation being that most of the universe has a peculiar velocity relative to him. And, he could do that. He would end up with a metric where he is at rest, the universe is expanding, and most of the things in the universe is in a reference frame that is not his own.

 

General relativity is the physics which is the same in both reference frames. FLRW assumes that all observers have the same cosmic time. That is not an assumption that general relativity makes. It is a simplifying condition that is made to simplify things. It is not a condition that has to be imposed.

 

I don't know if this is in conflict with the general or special principles of relativity.

 

It would not be. The principle doesn't require that every observer in the universe see the universe the same. It requires only that all observers be able to describe the universe with the same laws of physics. Relative to A, the universe follows GR, and relative to B, the universe follows GR.

 

~modest

[quantumtopology]

To respond to the title of this thread, I am gonna say that the paradox in the OP is probably only apparent, so no, expansion in itself does not contradict the relativity principle, I'm inclined to think.

However, the reasoning behind the question asks indirectly if the expanding hypothesis is not unnecessary to explain redshift, and if another expalanation for cosmological redshift was available, then the Occam's razor would have to be applied.

[LaurieAG]

Hi Modest, quantumtopology,

 

But, the objection 'things should be relative and this doesn't seem to be' is philosophical. It wouldn't be surprising if the rebuttal is equally philosophical.

...

Likewise simultaneity is relative so a statement (to be completely accurate) must read "these two events are simultaneous relative to y".

 

So, let's dissect the paradox. An observer, A, in the hubble frame sees the universe isotropically. An observer, B, with a velocity relative to the hubble frame does not see the universe isotropically. If velocity is relative in this situation then it would not make complete sense to say "B has a velocity but A does not". We would rather need to say "B has a velocity relative to most of the mass of the universe (or, to be more correct: "relative to the hubble flow") while A does not". Likewise, most of the mass of the universe has a velocity relative to B.

 

The closest thing we could get to this point A (or point y) would be a trajectory that was stationary relative to the center of our galaxy, the milky way, but not stationary relative to us. The velocity of this point relative to our galactic rotation path is easy to calculate, our distance around the galaxy/time taken to orbit, 2*pi*250,000LY/(4,000,000,000/20)yrs (2,354,564.459136 m/s or 654.045683km/hr or 0.00785398 % of c).

 

A series of observations made along this trajectory would soon tell us if things were as we thought or otherwise.

 

Modified Newtonian dynamics - Wikipedia, the free encyclopedia points in the general direction.

 

Finally, the uncertainties on the velocity of galaxies within clusters and larger systems have been too large to conclude in favor of or against MOND. Indeed, conditions for conducting an experiment that could confirm or disprove MOND may only be possible outside the Solar system. A couple of near-to-Earth tests of MOND have been proposed though: one involves flying the LISA Pathfinder spacecraft through the Earth-Sun saddlepoint[4]; another involves using a precisely controlled spinning disk to cancel out the acceleration effects of Earth's orbit around the Sun, and Sun's orbit around the galaxy[5]; if either of these tests are carried out, and if MOND holds true, then they should feel a slight kick as they approach the very low acceleration levels required by MOND.

[quantumtopology]

Hi Modest, quantumtopology,

 

 

 

The closest thing we could get to this point A (or point y) would be a trajectory that was stationary relative to the center of our galaxy, the milky way, but not stationary relative to us. The velocity of this point relative to our galactic rotation path is easy to calculate, our distance around the galaxy/time taken to orbit, 2*pi*250,000LY/(4,000,000,000/20)yrs (2,354,564.459136 m/s or 654.045683km/hr or 0.00785398 % of c).

 

A series of observations made along this trajectory would soon tell us if things were as we thought or otherwise.

 

Modified Newtonian dynamics - Wikipedia, the free encyclopedia points in the general direction.

 

Hi, Laurie

I don't quite get your reasoning and how it relates to the OP,nor what MOND has to do with it here.Probably my fault anyway. Can you clarify the connection?

 

But actually, the way Modest puts it there is not much of a paradox left.

 

Regards

QTop

[Pyrotex]

Let' remember that Occam's Razor is a "rule of thumb" not a "law".

The simplest explanation doesn't always have to be the way it its.

Bohr's simple atom made of electrons in orbit around a nucleas is a far simpler theory than the QM version with the electrons being just clouds of charge probability. But experiment verifies that the QM theory wins.

 

Just because an observation appears to contradict some accepted theory doesn't mean you have a paradox on your hands. There are other avenues to explore. Maybe the observation is flawed by some other attribute of the Cosmos that we don't know about yet. Maybe our accepted theory has restrictions at distances that are a major fraction of the visible Universe. Just what is "expansion"? Perhaps a different interpretation of expansion makes the problems go away. Maybe not.

 

We live in interesting times. And not all the data is in yet.

[quantumtopology]

Hi, Pyrotex.

Let' remember that Occam's Razor is a "rule of thumb" not a "law".

The simplest explanation doesn't always have to be the way it its.

Bohr's simple atom made of electrons in orbit around a nucleas is a far simpler theory than the QM version with the electrons being just clouds of charge probability. But experiment verifies that the QM theory wins.

I tend to agree with you about the Occam's razor not being always the right one but it is a good rule of thumb, nevertheless.

Remember that it only applies when the rest of checks on the hypothesis being compared are equal , so your example of Bohr's atom is not a good example, since that model was giving worst predictive results than QM.

 

There are other avenues to explore. Maybe the observation is flawed by some other attribute of the Cosmos that we don't know about yet. Maybe our accepted theory has restrictions at distances that are a major fraction of the visible Universe. Just what is "expansion"? Perhaps a different interpretation of expansion makes the problems go away. Maybe not.

 

We live in interesting times. And not all the data is in yet.

 

This is a very interesting thought that I would like to elaborate on:

 

This considerations should be obvious and ought to guide the normal development of scientific theories' advancement. But they don't, sadly. Rather the opposite, they are seen as threats by many.

In my opinion "expansion" might perfectly be a result of an interpretation, not necesarily flawed but compatible with another interpretation that as you say makes a lot of problems go away (like dark energy and dark matter, horizon problem, age problem for instance)

 

Regards

QTop

[modest]

Hi Modest, quantumtopology,

 

Good day.

 

...So, let's dissect the paradox. An observer, A, in the hubble frame sees the universe isotropically. An observer, B, with a velocity relative to the hubble frame does not see the universe isotropically....

 

The closest thing we could get to this point A (or point y) would be a trajectory that was stationary relative to the center of our galaxy, the milky way, but not stationary relative to us....

 

No, I believe the Milky Way has a velocity of about 500 km/s relative to the Hubble flow, so a person could get a bit closer than that.

 

"That exact fate befell Vera Rubin and W. Kent Ford, Jr., of the Carnegie Institution of Washington and two colleagues in the mid-1970s. Using complicated and (to hear some astronomers tell it) not entirely convincing measurements, they reported that the Milky Way, our galaxy, had a peculiar velocity of about 500 kilometers per second. In other words, the Milky Way was hurtling about 370 miles per second off the plumb of the big bang. Rubin in fact had suggested the same thing way back in 1950, but her data had been even sketchier, the reaction even chillier."

 

Hall, Stephen S. Mapping the Next Millennium. New York: Random House: 1992, 328, 334.

 

 

 

"These measurements, confirmed by the Cosmic Background Explorer satellite in 1989 and 1990, suggest that our galaxy and its neighbors, the so-called Local Group, are moving at 600 kilometers per second (1.34 million miles per hour) in the direction of the constellation Hydra."

 

Kraan-Korteweg, Renée C. & Ofer Lahav. "Galaxies Behind The Milky Way." Scientific America. October 1998.

 

~modest

[LaurieAG]

Hi QTop, Modest,

 

I don't quite get your reasoning and how it relates to the OP,nor what MOND has to do with it here.Probably my fault anyway. Can you clarify the connection?

 

Sorry my fault, I was going to post a much larger response but decided to break it up a bit.

 

To move from the philosophical to the physical, a repeatable experiment, that would support the original hypothesis, needs to be created.

 

The MOND Wiki refers to an experiment that would cancel out the acceleration effects of Earth's orbit around the Sun, and Sun's orbit around the galaxy. An observer at a point a, stationary relative to the center of our galaxy, would not have to cancel out these effects. Have a close look at my avatar, yes it is a screen capture of a feedback loop with lag and quite a bit of spin. The screen is a stationary point with respect to the flow.

 

No, I believe the Milky Way has a velocity of about 500 km/s relative to the Hubble flow, so a person could get a bit closer than that.

 

So a point located in the Hubble flow wouldn't violate any physical laws and a series of observations made from this respective point of view over time would tell us if any model derived from the reverse engineering of data was actually valid.

[quantumtopology]

 

To move from the philosophical to the physical, a repeatable experiment, that would support the original hypothesis, needs to be created.

 

The MOND Wiki refers to an experiment that would cancel out the acceleration effects of Earth's orbit around the Sun, and Sun's orbit around the galaxy. An observer at a point a, stationary relative to the center of our galaxy, would not have to cancel out these effects. Have a close look at my avatar, yes it is a screen capture of a feedback loop with lag and quite a bit of spin. The screen is a stationary point with respect to the flow.

I find very interesting these fedback loops that originate fractal patterns with spiral forms and vortices, might these optical tricks be related in any way with the flat velocity curves of spiral galaxies? It's possible, I'll think about it.

 

Regards

QTop

[LaurieAG]

Hi Qtop, Modest,

 

I find very interesting these fedback loops that originate fractal patterns with spiral forms and vortices, might these optical tricks be related in any way with the flat velocity curves of spiral galaxies? It's possible, I'll think about it.

 

I played around with feedback loops around 12 years ago and produced a few screen prints. Its amazing what you can do with heaps of spin and a bit of lag (you need mirror(s) for the fractals). With a deft touch you can induce a shadow into the feedback loop and create a stable Einstein ring type Halo from the perfect orb in my avatar. While this was a good example of the mechanics behind detecting planets around stars, it raises questions about what exactly is happening at much larger timescales.

 

About 10 years ago I wondered about looking at things from a different perspective. i.e. what straight path would the light, from a distant sun rotating around the center of its own 'galaxy', follow as it went towards an observervation point in another 'galaxy'. This observation point is 'stationary' relative to all of the light paths that are captured during the entire exposure period.

 

When you come from the opposite direction, with a full understanding of what is happening in the feedback loop, you see that the light paths from a single sun, like ours spinning around a central point, would look much like what we call a 'galaxy', especially if our observation captured at least one entire rotation in depth and width (and more so if we included the planets). The attached image shows the leading edges of where you would expect the straight line light to be coming from as it approaches the relatively stationary observation point.

 

This suggests that the cosmic time posited by big bang cosmology is not absolute time, since the time measurements are made relative to the privileged reference frame. For example, the assertion that the age of the universe is about [13.7] billion years old is elliptical for the statement “relative to the privileged reference frame, the universe is [13.7] billion years old.”

 

Any experiment would have to use some sort of distributed navigational feedback system to determine that it itself was stationary relative to the central pivot point of the universe prior to making observations. A truely thorough experiment would include multiple probes that followed different paths (for different theories/models) relative to a central observation unit that realigned itself to the probes actual path alignment before making observations. We'd be at the end of a chain of communications that led to a truely priveleged frame of reference, one way or the other.

[quantumtopology]

Hi Qtop, Modest,

 

 

 

I played around with feedback loops around 12 years ago and produced a few screen prints. Its amazing what you can do with heaps of spin and a bit of lag (you need mirror(s) for the fractals). With a deft touch you can induce a shadow into the feedback loop and create a stable Einstein ring type Halo from the perfect orb in my avatar. While this was a good example of the mechanics behind detecting planets around stars, it raises questions about what exactly is happening at much larger timescales.

 

About 10 years ago I wondered about looking at things from a different perspective. i.e. what straight path would the light, from a distant sun rotating around the center of its own 'galaxy', follow as it went towards an observervation point in another 'galaxy'. This observation point is 'stationary' relative to all of the light paths that are captured during the entire exposure period.

 

When you come from the opposite direction, with a full understanding of what is happening in the feedback loop, you see that the light paths from a single sun, like ours spinning around a central point, would look much like what we call a 'galaxy', especially if our observation captured at least one entire rotation in depth and width (and more so if we included the planets). The attached image shows the leading edges of where you would expect the straight line light to be coming from as it approaches the relatively stationary observation point.

 

 

 

Any experiment would have to use some sort of distributed navigational feedback system to determine that it itself was stationary relative to the central pivot point of the universe prior to making observations. A truely thorough experiment would include multiple probes that followed different paths (for different theories/models) relative to a central observation unit that realigned itself to the probes actual path alignment before making observations. We'd be at the end of a chain of communications that led to a truely priveleged frame of reference, one way or the other.

 

Hi, Laurie

Those are clever ideas indeed, I agree with the way you see the problem of the trajectories, in fact I had this insight some time ago about how the fact that we are observing from a non itruly inertial frame wrt the center of the galaxie affects our perspective of far away objects.

 

What would you think would be the outcome of the experiment you propose? What kind of trajectories would we observe?

 

Regards

QTop

[LaurieAG]

Hi QTop,

 

I agree with the way you see the problem of the trajectories, in fact I had this insight some time ago about how the fact that we are observing from a non itruly inertial frame wrt the center of the galaxie affects our perspective of far away objects.

 

What would you think would be the outcome of the experiment you propose? What kind of trajectories would we observe?

 

Irwin Hubble himself had some reservations about an expanding universe and the Hubble Flow appears to be his way of laying a solid foundation for future research that could resolve these reservations.

 

Edwin Hubble - Wikipedia, the free encyclopedia

 

Hubble believed that his count data gave a more reasonable result concerning spatial curvature if the redshift correction was made assuming no recession. To the very end of his writings he maintained this position, favouring (or at the very least keeping open) the model where no true expansion exists, and therefore that the redshift "represents a hitherto unrecognized principle of nature."[6]

 

One outcome of such an experiment would be that the data from this observation point could be compared with the outcomes projected by current models and theories. In effect its navigation and positioning system would just be a subset of its total observational capacity/potential that could be used to compare the actual with the expected or the unexpected.

 

Whatever the outcomes feedback loops will play an important part in them.

 

The two attached images show what happens when the observation point (camera) is too close or too far away from the view horizon (or pointing too far left or right?).

 

In the scale of my feedback loop that's about 10% of the physical path, in my 'galaxy' model the depth of one rotation is a greater percentage.

 

Cheers, Laurie