Light as speed limit?

[marcopololu]

Currently we believe that light travels at C which is constant and nothing can exceed it, so I thought of something that also relates to the expanding universe.

 

Would it not make more sense to say that light travels at maximum speed and that the universe has a speed limit, thus light travels at the speed limit which is C?

 

It would mean that as the universe continues to expand at an increasing rate, it would eventually expand at the speed of light and not go any faster.

 

This would be the reason for the universe to have a speed limit because if one were to travel past the speed of light it would mean that one would eventually outspeed the rate of the universe's expansion thus arriving at the speed of the universe and go outside it.

 

Also, if the universe's expansion exceeds the speed of light, would it also raise the speed limit and allow light to travel faster?

 

Please discuss if this is probable.

[The Bear's Key]

The universe already expanded faster than light during/after the Big Bang. It continues to expand today.

 

It doesn't expand by movement, rather it's because new space is created everywhere, therefore even now stars recede from one another.

 

Light's speed is constant, so naturally scientists deduce it wont ever change -- no matter how quickly the universe expands.

[cypress]

General relativity theory precludes the possibility of particles traveling faster than C, thus expansion in every direction from a constant reference frame is disallowed. Perhaps opposite wave fronts exceed the speed of light relative to each other, but I don't see how the expansion can be termed as greater than the speed of light. The mass of the universe is of course traveling outward much slower than the radiation wave front and this expansion of mass is generally taken to be the referred to as the expansion of the universe. Maybe you can explain better your claim.

[Sisyphus]

The Bear's Key is right. The universe does expand by moving. Distant galaxies get farther and farther away from us, but not because we are moving away from one another. They are receding because the amount of space in between us is increasing.

 

This is a difficult distinction to grasp, but it is extremely important. Nothing can move faster than C (the speed of light) relative to anything else. That is true. It is also true that there are objects getting farther away from us at a rate faster than the speed of light, and there always have been.

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Perhaps opposite wave fronts exceed the speed of light relative to each other,

 

No object has a velocity greater than C relative to any other object.

 

The mass of the universe is of course traveling outward

 

Stop right there. The expansion of the universe is not "outward." It's not like an explosion, and it does not involve actual motion. There is no central point that everything is expanding away from, and no outer edge. Distances are increasing. That's all.

[swansont]

Would it not make more sense to say that light travels at maximum speed and that the universe has a speed limit, thus light travels at the speed limit which is C?

 

This is indeed the case; massive particles move at speeds below c and massless particles move at c.

[marcopololu]

The universe already expanded faster than light during/after the Big Bang. It continues to expand today.

 

It doesn't expand by movement, rather it's because new space is created everywhere, therefore even now stars recede from one another.

 

Light's speed is constant, so naturally scientists deduce it wont ever change -- no matter how quickly the universe expands.

 

Ah, I forgot that expansion isn't movement so it's not based on velocity. Thank you for the answer.

[pioneer]

Originally Posted by The Bear's Key

The universe already expanded faster than light during/after the Big Bang. It continues to expand today.

 

It doesn't expand by movement, rather it's because new space is created everywhere, therefore even now stars recede from one another.

 

Light's speed is constant, so naturally scientists deduce it wont ever change -- no matter how quickly the universe expands.

 

The problem with this lies in comparative proof. It is easier in the lab to expand a block of mass thereby expanding the gravity field and the local space-time, than to add space-time between matter out of nothing, so nothing has to move. Has anyone demonstrated the latter in the lab? I tend to think this assumption is an illusion, based on circumstantial evidence, until someone could prove it can be done in the lab.

 

Just because the math says so, does not the mean the conclusions of the math are real. As proof of this statement, there is a direct relationship between graphical and mathematical representations of data. These are two ways to do the same thing with graphing easier. Below is a graphical representation, which if one wanted to translate, could be expressed with equations. It is called the stairway to nowhere. It can exist on paper and be expressed with equations, even though it can not exist in reality. I have always assumed the expanding space-time effect is a stairway to nowhere that fools the experts; clever magic trick, until lab proof.

 

 

 

[swansont]

General relativity has been tested in many ways. It predicts expansion of spacetime, if one does not kluge a cosmological constant onto it.

[cypress]

The Bear's Key is right. The universe does expand by moving. Distant galaxies get farther and farther away from us, but not because we are moving away from one another. They are receding because the amount of space in between us is increasing.

 

This is a difficult distinction to grasp, but it is extremely important. Nothing can move faster than C (the speed of light) relative to anything else. That is true. It is also true that there are objects getting farther away from us at a rate faster than the speed of light, and there always have been.

 

Hmm. Is this concept or confirmed? Can you demonstrate this is factually correct or does the evidence provide alternative explanations?

 

Stop right there. The expansion of the universe is not "outward." It's not like an explosion, and it does not involve actual motion. There is no central point that everything is expanding away from, and no outer edge. Distances are increasing. That's all.

 

I'm not sure that there is no further description possible than simply space expanding without kinematic motion. Certainly in one reference frame the universe can be viewed as if it were expanding as you describe, but is it the only explanation, is it the only way to describe it? Certainly not.

[Sisyphus]

All of the workable models involve cosmic expansion. Are there alternative explanations that work just as well? Perhaps, but nobody has come up with any yet. An explosion-like expanding sphere of moving matter, however, is demonstrably false.

[michel123456]

Would it not make more sense to say that light travels at maximum speed and that the universe has a speed limit, thus light travels at the speed limit which is C?

 

I will surely look stubborn, but I disagree with this statement, & with Swansont.

Why?

Because I stick desesperately to the concept of speed as a relative concept. I believe C is the speed limit of our observation. No one, from any FOR, can observe anything moving at speed higher than C. That's all.

IMHO of course.

[swansont]

What is important is what you can substantiate with evidence, and models which lack expansion fail to predict/explain critical pieces of evidence. Opinions don't count as falsification.

[cypress]

All of the workable models involve cosmic expansion. Are there alternative explanations that work just as well? Perhaps, but nobody has come up with any yet. An explosion-like expanding sphere of moving matter, however, is demonstrably false.

 

So it is not incorrect to describe an alternate reference frame whereby matter near the boundary is moving outward relative to the universes center of gravity.

 

I don't recall in my description the use of of any term indicating an explosion in a fixed pre-existing spacial continuum, so I am confused why choice of description for expansion should matter, particularly when we don't fully understand the nature or mechanism of this expansion. I am interested in the evidence that the rate of increase in the distance between a celestial body and the universes center of gravity exceeds the speed of light as would be required to describe the expansion of the universe as Bear Key did.

[swansont]

There is no center of gravity that you can identify.

[michel123456]

There are billions of billions of billions of centers of gravity. You cannot say there is none: there are too manies.

[Spyman]

So it is not incorrect to describe an alternate reference frame whereby matter near the boundary is moving outward relative to the universes center of gravity.

The Big Bang is not an explosion of matter moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distance between two comoving points. Because the FLRW metric assumes a uniform distribution of mass and energy, it applies to our Universe only on large scales—local concentrations of matter such as our galaxy are gravitationally bound and as such do not experience the large-scale expansion of space.

http://en.wikipedia.org/wiki/Big_Bang

 

The key to avoiding the misunderstandings is not to take the term “big bang” too literally. The big bang was not a bomb that went off in the center of the universe and hurled matter outward into a preexisting void. Rather it was an explosion of space itself that happened everywhere, similar to the way the expansion of the surface of a balloon happens everywhere on the surface.

http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf

 

 

I am interested in the evidence that the rate of increase ... exceeds the speed of light

While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, there is no such theoretical constraint when space itself is expanding. It is thus possible for two very distant objects to be moving away from each other at a speed greater than the speed of light (meaning that one cannot be observed from the other). The size of the observable universe could thus be smaller than the entire universe.

 

It is also possible for a distance to exceed the speed of light times the age of the universe, which means that light from one part of space generated near the beginning of the Universe might still be arriving at distant locations (hence the cosmic microwave background radiation). These details are a frequent source of confusion among amateurs and even professional physicists.

http://en.wikipedia.org/wiki/Metric_expansion_of_space

 

Observational evidence

Theoretical cosmologists developing models of the universe have drawn upon a small number of reasonable assumptions in their work. These workings have led to models in which the metric expansion of space is a likely feature of the universe. Chief among the underlying principles that result in models including metric expansion as a feature are:

 

- the Cosmological Principle which demands that the universe looks the same way in all directions (isotropic) and has roughly the same smooth mixture of material (homogeneous).

- the Copernican Principle which demands that no place in the universe is preferred (that is, the universe has no "starting point").

 

Scientists have tested carefully whether these assumptions are valid and borne out by observation. Observational cosmologists have discovered evidence - very strong in some cases - that supports these assumptions, and as a result, metric expansion of space is considered by cosmologists to be an observed feature on the basis that although we cannot see it directly, scientists have tested the properties of the universe and observation provides compelling confirmation. Sources of this confidence and confirmation include:

 

- Hubble demonstrated that all galaxies and distant astronomical objects were moving away from us, as predicted by a universal expansion. Using the redshift of their electromagnetic spectra to determine the distance and speed of remote objects in space, he showed that all objects are moving away from us, and that their speed is proportional to their distance, a feature of metric expansion. Further studies have since shown the expansion to be extremely isotropic and homogeneous, that is, it does not seem to have a special point as a "center", but appears universal and independent of any fixed central point.

- In studies of large-scale structure of the cosmos taken from redshift surveys a so-called "End of Greatness" was discovered at the largest scales of the universe. Until these scales were surveyed, the universe appeared "lumpy" with clumps of galaxy clusters and superclusters and filaments which were anything but isotropic and homogeneous. This lumpiness disappears into a smooth distribution of galaxies at the largest scales.

- The isotropic distribution across the sky of distant gamma-ray bursts and supernovae is another confirmation of the Cosmological Principle.

- The Copernican Principle was not truly tested on a cosmological scale until measurements of the effects of the cosmic microwave background radiation on the dynamics of distant astrophysical systems were made. A group of astronomers at the European Southern Observatory noticed, by measuring the temperature of a distant intergalactic cloud in thermal equilibrium with the cosmic microwave background, that the radiation from the Big Bang was demonstrably warmer at earlier times. Uniform cooling of the cosmic microwave background over billions of years is explainable only if the universe is experiencing a metric expansion.

 

Taken together, the only theory which coherently explains these phenomena relies on space expanding through a change in metric. Interestingly, it was not until the discovery in the year 2000 of direct observational evidence for the changing temperature of the cosmic microwave background that more bizarre constructions could be ruled out. Until that time, it was based purely on an assumption that the universe did not behave as one with the Milky Way sitting at the middle of a fixed-metric with a universal explosion of galaxies in all directions (as seen in, for example, an early model proposed by Milne). Yet before this evidence, many rejected the Milne viewpoint based on the Mediocrity principle.

 

Additionally, scientists are confident that the theories which rely on the metric expansion of space are correct because they have passed the rigorous standards of the scientific method. In particular, when physics calculations are performed based upon the current theories (including metric expansion), they appear to give results and predictions which, in general, agree extremely closely with both astrophysical and particle physics observations. The spatial and temporal universality of physical laws was until very recently taken as a fundamental philosophical assumption that is now tested to the observational limits of time and space. This evidence is taken very seriously because the level of detail and the sheer quantity of measurements which the theories predict can be shown to precisely and accurately match visible reality. The level of precision is difficult to quantify, but is on the order of the precision seen in the physical constants that govern the physics of the universe.

http://en.wikipedia.org/wiki/Expansion_of_the_universe#Observational_evidence

[swansont]

There are billions of billions of billions of centers of gravity. You cannot say there is none: there are too manies.

 

I don't even know what that means.

 

Canter of gravity (aka center of mass) is a well-defined concept; the point is unique. If there is one.

[michel123456]

I don't even know what that means.

 

Canter of gravity (aka center of mass) is a well-defined concept; the point is unique. If there is one.

 

I have an obvious problem when trying to explain some concepts of mine.

 

Each particle with mass has a center of gravity. When many particles are tied together making a macroscopic object, there is one and only one center of gravity for this particular object. The universe is made up with billions of particles & billions of macroscopic objects with billions of billions individual centers of gravity.

 

When one discuss about the BBT, the expansion of space, or the "change in metric", all these happen in the gap between all those individual "centers of gravity".

 

As you said, there is no (single specific) center of gravity that you can identify, because each individual center is equally good. (words in italic are mine).

You can decide and take any point as the center of gravity of the universe, it must work. That is also part of the Copernican Principle si je ne m'abuse.

[swansont]

We are talking about the center of gravity of the universe. Not of individual components. I'm not saying there are many and they are equally good. I'm saying you can't find one.

[michel123456]

We are talking about the center of gravity of the universe. Not of individual components. I'm not saying there are many and they are equally good. I'm saying you can't find one.

 

And I say any can do.

Edited June 22, 2010 by michel123456
any instead anyone

[zapatos]

Stop right there. The expansion of the universe is not "outward." It's not like an explosion, and it does not involve actual motion. There is no central point that everything is expanding away from, and no outer edge. Distances are increasing. That's all.

 

So if everything in the universe suddenly reversed direction, it wouldn't eventually end up in the same place? What did the universe look like in the beginning (meaning roughly 13.7 billion years ago)? Are you saying that without the expansion of space, galaxies would no longer be moving away from each other?

[Sisyphus]

So if everything in the universe suddenly reversed direction, it wouldn't eventually end up in the same place?

 

Yes. The directions that things are moving in is more or less random, and over large distances motion is a small effect compared with expansion.

 

What did the universe look like in the beginning (meaning roughly 13.7 billion years ago)?

 

Best I can do:

 

http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang

 

Are you saying that without the expansion of space, galaxies would no longer be moving away from each other?

 

Yes.

[cypress]

There is no center of gravity that you can identify.

 

That would be just one of the difficulties in demonstrating Bear's Key assertion seconded by sisyphus. Without a defined reference it is difficult to establish that the rate of expansion exceeds some defined speed.

 

As a note to Spyman; I think you may have completely misunderstood the purpose of my response. First, regardless of the actual mechanism whereby the universe is expanding, the alternative reference frame I described is not incorrect. Second, while I appreciate the evidence you offered that supports isotropic and homogeneous expansion, note that there are indeed alternatives that are consistent with these observations that do not rely on the assumptions outlined in the article you copied. Finally I don not dispute that the universe is expanding, nor do I dispute that it is doing so remarkably uniformly.

 

I did however ask for evidence that the rate of this uniform expansion exceeds or once exceeded the speed of light. That question has not yet been addressed.

 

Mitchel: A finite space with mass necessarily must have but one center of gravity, even if we are unable to locate it. The Universe is known to be finite, therefore it would seem that it must have one center of gravity.

[swansont]

That would be just one of the difficulties in demonstrating Bear's Key assertion seconded by sisyphus. Without a defined reference it is difficult to establish that the rate of expansion exceeds some defined speed.

 

The did not specify that the expansion was relative to a center of gravity. A defined reference is one we define.

[cypress]

The did not specify that the expansion was relative to a center of gravity. A defined reference is one we define.

 

Perhaps I a wrong, but I believe he implied it by speaking of "the expansion rate" as opposed to "one measure of the expansion rate" or some "localized expansion rate". If the expansion rate of the universe is uniform as Bear's Key implied, and Spyman stated directly, then it would apply regardless of the reference frame. I mention a specific reference only to be clear so as to avoid semantic issues.