# Looking Back Through Spacetime in the Future

1. Sep 15, 2010

### PhanthomJay

Just wondering. The Hubble looks back 13 billion light years and photographs galaxies in their early formative stages not too long after the Big bang. Now lets say 13 billion years from now, if man and woman and galaxies are still alive, the version of the Hubble, in the year 13,000,002,010AD, looks back into the deep field like it has done recently. Will it now see those same galaxies, as they exist today, by our time, and which which can have no information about at this time, ...will they appear as full blown galaxies when the Hubble looks back 13 billion light years 13 billion years from now? and if it looks back 26 billion light years, what will it see? I know spacetime expansion is going to mess this question up, but once we believed in a static universe, so i'm wondering what Hubble would see 13 billion years from now when it looked back 26 billion light years in a say finite unbounded static universe, if you catch what I'm saying, which may not make sense. Thanks.

2. Sep 15, 2010

### Rebound

We would receive the light that left those galaxies a number of years ago that is equal to their distance in light years whether the observation is made 1 or a 100 or a billion years from now. So, they will look like whatever they would look like after whatever much time has passed since the last observation.

3. Sep 15, 2010

### PhanthomJay

Well yes, that makes sense, but i guess what i'm driving at, is that those early galaxies are 13 billion years old now, by our measure of time, and probably huge, and massive, but we cannot see them nor detect their gravity yet, so how do we determine the mass of the universe (mattter /dark matter) if we don't have any information about them as they exist today? And please don't forget part 2 of my question. Thanks.

4. Sep 15, 2010

### PhanthomJay

Oh, wait a sec, I forgot that mass and energy is always conserved, so maybe those early galaxies have now combined into one giant galaxy.....but I'd still like to know what Hubble would see 13 billion years from now when it looks 26 billion light years away...for both the the case of an expanding universe and a hypothetical 'static' universe...

5. Sep 17, 2010

### Rebound

Good question. If current ideas about the evolution of the universe and my understanding of them are correct, there are several processes that may each have an effect.

1. There will be a tendency for matter to become more and more consolidated if it is left to itself.
2. If the universe continues to expand at an accelerating rate, it will eventually overcome the force of gravity at the largest scales (galactic superclusters), and then it will progressively tear apart ever smaller structures. I don't know how long this has been calculated to take but I believe it would begin to have a noticeable effect within the next 13 billion years.
At this point my knowledge gets a bit fuzzy so it may get a bit ambiguous.
3. It is known that the space between galaxies in clusters contains a large amount of very hot gas*. I'm not sure, but I think it is kept that way from energy pumped into it by the surrounding galaxies. As they age, the stars in those galaxies will burn out; few new stars will be born because the gas within the galaxy has been depleted and these galaxies will go dark. If the temperature is the surrounding gas begins to fall and the gas spreads out, there will be a new burst of star formation and while the galaxies we observe now will have gone dark, there will be a huge amount of new star formation going on that looks nothing at all like it does now.

Conclusion? It all depends on how long all these process will take but we're talking about structures which are already very old. I think we'll find that these oldest structures will just get denser and dimmer until they fade from view entirely. Don't forget that distance itself will cause fewer and fewer photons to reach us as well even if these galaxies continue to produce as much energy as they do now. You may be asking yourself why I didn't just say this at the start but it sounded like you were also interested in what they would look like if we were able to observe them.

*In the area of 10 million degrees if memory serves.

6. Sep 18, 2010

### PhanthomJay

yes, thanks for the response!