Expanding distance

[Riogho]

Okay, I know the universe is expanding faster then the speed of light, so I have a few questions.

 

Is it possible that there are galaxies out there that even when they emit light since they are traveling faster away from us then light is traveling toward us that we never see them.

 

Also, is ALL of space expanding at this rate or just the edges? I really don't understand how that works either.

 

And since space is expanding when we measure the distance from one place to another using light sources are we taking into account the expanding universe?

 

Thanks, from a n00b.

[swansont]

Martin has set up several links that answer the basics of the big bang and expansion

 

http://www.scienceforums.net/forum/showthread.php?t=30900

[antimatter]

It's not continuously expanding at the speed of light, it may have at one point, but there's really no way of knowing.

[Martin]

It's not continuously expanding at the speed of light, it may have at one point, but there's really no way of knowing.

 

*sigh*

 

antimatter we can SEE hundreds of objects that are currently receding from us at >c

and which were receding at >c when they emitted the light which we are now receiving.

 

 

there's no other way to construct a universe to fit the pattern of redshift and distance data

 

besides, it is hardly surprising since recessionspeed is not what Special Relativity talks about---so what I'm saying about >c does not contradict Einstein SR. In fact what I'm saying is forced by Einstein GR.

 

So would you stop contradicting the old guy?

or else present us with your own theory of General Relativity to replace Einstein's.

[antimatter]

Whoops, sorry...

what do you mean 'stop contradicting the old guy',

this is one time I made a mistake...

[Martin]

Okay, I know the universe is expanding faster then the speed of light, so I have a few questions.

 

The universe has no known radius and no well-defined edges, so it may or may not have a well-defined size. It might be spatially infinite. So what you mean is that a lot of the DISTANCES in the universe are expanding > c.

 

Is it possible that there are galaxies out there that even when they emit light since they are traveling faster away from us then light is traveling toward us that we never see them.

 

Absolutely! Any galaxy that is currently receding at over 120% of the speed of light can no longer send us a signal that will reach us-----this is according to the standard LCDM model that most cosmologists use nowadays.

 

If a galaxy is currently receding just 1% faster than c, or just 10% faster than c, then the light it emits today WILL eventually reach us.

 

But according to standard cosmology there is a kind of horizon between 16 and 17 billion LY away where things are receding over 20% faster than light and anything beyond there cannot reach us with a signal. It is called the "cosmological event horizon".

 

We can see those objects as they were in the past. Light they emitted in the past is now reaching us. The limitation is that light they emit at this moment can never reach us. It is because of acceleration---accelerated expansion.

 

Also, is ALL of space expanding at this rate or just the edges? I really don't understand how that works either.

 

In ordinary mainstream cosmology there are no edges.

I don't know of any crackpot cosmologies that have edges, but maybe there are some.

 

Distances are expanding at a rate of 1 percent every 140 million years. The longer a distance is today, the faster it is expanding (because they all expand by a fixed percent).

 

And since space is expanding when we measure the distance from one place to another using light sources are we taking into account the expanding universe?

 

For sure

You tell me a redshift and I will tell you the distance the object WAS when it emitted the light, and the distance it IS NOW at the moment the light gets here, and I will tell you how long the light was in transit.

 

the standard cosmology model (LCDM) has been built into calculators that do that kind of calculation for you automatically. expansion is DEFINITELY taken into account, that's the point of having the model:-)

 

Whoops, sorry...

what do you mean 'stop contradicting the old guy',

this is one time I made a mistake...

 

I didn't mean to sound serious. It is just that Einstein says distances in cosmology must expand faster than light. Currently, right now as we speak.

And you seemed to be contradicting this.

 

To put it simply. If you solve the GR equation so as to get a good fit to what we observe, then the rate of expansion is proportional to the distance. Short distances expand slowly. Distances of around 14 billion LY expand at speed of light. Longer distances expand faster.

 

Very short distances like within our own Milkyway galaxy do not expand at all.

 

You were saying that distances DON'T expand faster than light. That contradicts Einstein in the sense that modern cosmology is just Einstein GR fit to the observational data.

[Riogho]

Short distances in our own galaxy don't expand at all, or do they just expand so small it's irrelevent?

[insane_alien]

expansion is way too small to notice.

[Mr Skeptic]

expansion is way too small to notice.

 

Isn't its expansion canceled by gravity?

[insane_alien]

no, but the force of gravity exceeds the 'force'(it is a pseudo force like centrifugal force in a rotating frame of reference). it is still there but the signal:noise ratio sucks.