Galaxies

Seeruk

This is my first post on this message board. So if this message does not represent itself the way I am trying to express it, I apologize in advance.

Based on an article in Scientific American March 2005 addition, it stated that galaxies recede faster than light.

"The recession of a galaxy away from us (v) is directly proportional to its distance from us (d), or v = Hd. The proportional constant, H, is known as the Hubble constant and qualifies how fast space is stretching - not just around us but around any observer in the universe."

This is my views from what I gathered from different sources:
This is Hubble's law. It goes on to say that when a galaxy travels in space it increases in speed as it nears the Hubble distance. The Hubble distance is a curve in space where light exists on one side and not the other. The Hubble distance barrier is not constant, it continues to move further outward. The relative Velocity of space increases as space expands constantly. Where light occurs on one side of the Hubble distance, the laws of physics take place. On the other side the laws do not take place. Once light passes the Hubble distance it now moves faster than the speed of light. Thus if light can not be seen or subject to physics, it can not be measured. This may be why Einstein said nothing can move faster than the speed of light. If the Hubble distance is not constant, than if the barrier moves behind the Galaxy that is already going faster than the speed of light it would now be behind the Hubble distance and subject to the laws of physics and Einstein's concept. Would it not be Galactic chaos? The force on the Galaxy going from faster than to slower than the speed of light would be tremendous. An example supporting my hypotheses is a toy top. As it spins it gains speed,as you continue to spin, it will gain enough momentum to move. If a force comes in contact with the spinning object it causes a negative reaction in the tops movements. Thus the object becomes unbalanced and unpredictable. I believe, the same effect should happen to Galaxies. Why does this not occur.
-Seeruk

Rade

Is it possible for light to "pass" the Hubble distance -- or does the Hubble distance serve as a "limit" for the movement of light toward it ? Also, see these links for recent experiment that has documented that "light" can travel faster than speed of light:
http://www.scienceblog.com/light.html
http://www.livescience.com/technolog...fastlight.html
as well as "solitons": (defined here: http://en.wikipedia.org/wiki/Soliton)
http://prola.aps.org/abstract/PRD/v63/i12/e126004

Seeruk

For what I can find out light passes the hubble distance. They say recession velocity can move faster than light and it still does not violate the special relativity rule. It is also mentioned that it is still true that nothing can overtake a beam of light.

Thank you for the links Rade and I hope this answers your questions.

vincentm

i thought nothing can exceed the speed of light?

selfAdjoint

(Sigh) We should have a FAQ on this. How many times has this question been asked.

The galaxies are not moving through space away from us, the space between us and them is expanding. This is not a velocity and it can happen so fast that the distance between us and the galaxies increases faster than light, but nothing is moving faster than light.

vincentm

Thanks, that makes perfect sense. It's kinda like this image explains.

DrChinese

Welcome to PhysicsForums, Seeruk!

The situation as described above is accurate. It is important to realize that many articles and discussions of physics necessarily use shorthand terminology. Such terminology is often later used out of context. So you need to make sure you are working within the right context before you can expect to understand it.

General Relativity (GR) is the theory used to describe the interaction of spacetime and mass. While there are a few things which are not known about cosmology and GR, there are many that are known. The discovery of galaxies receding at speeds much faster than the speed of light (c) has led to this realization: our universe is not flat but is actually expanding at an accelerating rate. This is completely consistent with some GR scenarios.

It may seem impossible, but light from such receding galaxies can reach us even though the speed of the light particles does not ever exceed c locally. The details of this are fairly complicated, and a reference can be provided if you want to read something technical.

I would not think of the Hubble distance as some kind of curtain beyond which we cannot see. There is no point in our universe at which the laws of physics change (that we know of) or that c is different. Keep in mind that c is a constant value describing the speed of light particles in a "vacuum". The speed of light in varying mediums can be modified as described in some of the references above; however, that does not change the value of c.

Labguy

It is explained here, again. And, for those who haven't, please go to the top of the page and read the whole FAQ. That will help keep the number of questions about the basics at a minimumis right on.

Symbreak

While I agree with most of this, its important not to disregard the motions of galaxies as simply a byproduct of the Universes expansion.

'Space-time expansion' is a dubious concept. How do we know 'space' is expanding without matter? By definition, space can not even be measured without the existence of objects: thus, the 'expansion of the universe' is infered from the motions of matter. In GR, the very existence of space is redefined as the relations between interval-events.
So saying 'it is space which expands' is not entirely correct, since space (or time) cannot exist of itself.

Falworth

Don't confuse galaxy velocity with expansion of space. They are not the same. Space can expand faster than the speed of light and doesn't violate relativity. Nothing is moving, just space is expanding.

Phobos

How about examining the characteristics of the Cosmic Microwave Background?

Since we can't directly measure the proper motion of distant objects, the expansion is inferred from things like the redshifting of light from those objects.

So you're saying spacetime doesn't exist and it's all just an illusion based on our measurements of matter? Sounds like you'll need to replace GR.

HallsofIvy

How can you say "The Hubble distance is a curve in space where light exists on one side and not the other." and then argue that light moves "faster than the speed of light" on one side of the Hubble distance and "at the speed of light" on the other? You just said there was NO light on the other side of the Hubble distance to move at all!

Pi_314B

This is paraded around as if it were indisputable fact. I always keep this subject open for discussion, because of the (fact) that expansion of space is not a slam dunk. The possibilty that no galaxy recedes from us past the speed of light is most definitely still a possibility. I would consider myself remiss to not consider it as a potential. We could easily be wrong for hundreds of years taking on this sort of practice of perhaps the blind leading the blind.

εllipse

- Einstein, Relativity: The Special and General Theory, Appendix 5: Relativity and the Problem of Space

turbo

Darn, Pi! you should be be prepared to be treated like the village idiot for even suggesting such a thing around here. The mere suggestion that the Hubble relationship (reshift=distance) is not proof of the expansion of the universe can earn you insults and dismissal in these parts, IF your threads are not summarily shut down. Edwin Hubble would probably be shut down here repeatedly, since he was uncomfortable with the interpretation that the redshift=distance relationship must be interpreted as evidence of universal expansion.

If "empty" space is a transmissive medium, and light can lose energy by crossing it, we should expect that the redshift=distance relationship will give us a pretty good approximation of the density of "empty" space that light traverses between any distant source and our receptors. This is all well and good if you believe in classical optics, but the GR notion that the speed of light in a "vacuum" is invariable is a little too firmly entrenched in the minds of the faithful to allow reasonable consideration of the concept that light may be redshifted by interaction with the space that it traverses.

I hope you're ready for the ride. Good luck!

turbo

Thank you for that quote! Epistemology was not a mere mental exercise for Einstein. He was quite willing to consider the properties of space whether it was fully inhabited by sensible matter or devoid of it.

Chronos

Hubble was resistant to the concept of redshift = distance, and Einstein was resistant to the concepts of quantum physics. Both men would probably reassess their position if presented with the body evidence since accumulated. That does not diminish their achievements, nor do their achievements diminish the findings of those who stood upon their shoulders. In fact, I suspect they would be quite proud of the fruit their efforts inspired.