Dumb astrophysics question for clever twats

Re: Dumb astrophysics question for clever twats

Postby pErvinalia » Tue Dec 05, 2017 5:25 am

L'Emmerdeur wrote:
pErvinalia wrote:What bugs me about all this malarky is that we're told we can't use space-time itself as a reference field, yet we can reference it plenty enough when we declare that it is expanding.


I'm not sure where you picked that up. How is space-time being used as a reference in regard to the expansion of the Universe?


What's the universe expanding in relation to?


pErvinalia wrote:The other thing I always struggle with is the concept that when we see things that are say 14billion light years away we are looking back to the beginning of the universe.


Not exactly. Astronomers can observe objects that existed in a much earlier era, but not all that close to the beginning. The most distant (and most ancient) object observed so far is the galaxy GN-z11. It's approximately 32 billion light-years away and its light took about 13.4 billion years to reach us. When that light left GN-z11, the Universe was already about 400 million years old.


That's what I mean.

pErvinalia wrote:Where does this suppose that the light has been hanging around in for the last 14 billion years? It should have been way past us to the outer reaches of the universe.


The light has been travelling to us during those 13.4 billion years, while the Universe continued to expand. The light waves have been 'stretched' as they travelled by the Doppler effect.


But we were a lot closer to the emitter 14bya. I assume the answer is that space-time itself expanded since then, but that leads back to my first question - expanded in relation to what?
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Re: Dumb astrophysics question for clever twats

Postby pErvinalia » Tue Dec 05, 2017 5:29 am

L'Emmerdeur wrote:
pErvinalia wrote:Shouldn't there also be a giant hollow in the centre of the universe? Unless the expansion is greater further from the 'centre' of the universe.


There is no evidence that the Universe has anything we would be able to recognize as the centre. See the 'raisin pudding/raisin cake' analogy--from any object in the Universe an observer will see all other objects (aside from those in the immediate neighborhood that are gravitationally bound) moving away from the observer. Again, objects that are farther away are observed to be moving away at a higher speed.


Yeah, see how there's a hollow in the centre of the animation at that link.

But if the expansion is greater further out, then this would reduce the hollow effect.
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Re: Dumb astrophysics question for clever twats

Postby pErvinalia » Tue Dec 05, 2017 5:54 am

The other question about all this is that if space-time is expanding, then distant celestial objects outside of our super cluster should always remain the same relative size. That is, I wouldn't expect us to ever appear alone in the universe even after a hundred billion years (if we somehow managed to avoid Andromeda).
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Re: Dumb astrophysics question for clever twats

Postby L'Emmerdeur » Tue Dec 05, 2017 8:15 am

pErvinalia wrote:
L'Emmerdeur wrote:
pErvinalia wrote:What bugs me about all this malarky is that we're told we can't use space-time itself as a reference field, yet we can reference it plenty enough when we declare that it is expanding.


I'm not sure where you picked that up. How is space-time being used as a reference in regard to the expansion of the Universe?


What's the universe expanding in relation to?


Observations up to now have shown no special reference point in space-time, so the expansion consists of objects in relation to each other. The Cosmological Principle states that the Universe is isotropic on very large scales--put simply, any one place is much like another if the observer looks at a large enough area. Much of the data we have so far appears to strongly support this.

While there is a fellow who's promoting something called 'The Expanding Spacetime Theory,' it isn't anywhere near being a mainstream idea.

pErvinalia wrote:
L'Emmerdeur wrote:
pErvinalia wrote:The other thing I always struggle with is the concept that when we see things that are say 14billion light years away we are looking back to the beginning of the universe.


Not exactly. Astronomers can observe objects that existed in a much earlier era, but not all that close to the beginning. The most distant (and most ancient) object observed so far is the galaxy GN-z11. It's approximately 32 billion light-years away and its light took about 13.4 billion years to reach us. When that light left GN-z11, the Universe was already about 400 million years old.


That's what I mean.


OK, what is the part that you struggle with?

pErvinalia wrote:
L'Emmerdeur wrote:The light has been travelling to us during those 13.4 billion years, while the Universe continued to expand. The light waves have been 'stretched' as they travelled by the Doppler effect.


But we were a lot closer to the emitter 14bya. I assume the answer is that space-time itself expanded since then, but that leads back to my first question - expanded in relation to what?


Galaxies/galaxy clusters are observed to be moving away from each other. One way of looking at it is that space-time is expanding, but that would imply that there's something that it's expanding into. Since the Universe is defined as 'everything there is' that hypothetical something is just part of the Universe. Non space-time, but still part of the Universe? I think I've reached the limits of my knowledge here. :lol:
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Re: Dumb astrophysics question for clever twats

Postby pErvinalia » Tue Dec 05, 2017 8:43 am

If space-time is expanding, they can't be moving further apart, as units of measurement are expanding at the same rate.

I'm sure the theorists are right about this stuff, it's just that I find the pop sci explanations we get from them/magazines really inadequate.
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Re: Dumb astrophysics question for clever twats

Postby rainbow » Tue Dec 05, 2017 9:05 am

JimC wrote:How many Americans still think the whole shebang was created 6000 years ago?

Why did God go to all that effort to change the rate of decay of carbon-14, if he didn't want us to think that the Earth is only 6000 years old?
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Re: Dumb astrophysics question for clever twats

Postby Brian Peacock » Tue Dec 05, 2017 9:09 am

For the same reason he buried all those dinosaur bones.
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Re: Dumb astrophysics question for clever twats

Postby Tyrannical » Tue Dec 05, 2017 11:59 am

Galaxies accelerating at an accelerating speed apart.
The expansion of space that can move an 8 billion year old object 12 billion light years distance.
The need for dark matter/energy to explain how galaxies behave.


I think those are the current big 3 questions.
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Re: Dumb astrophysics question for clever twats

Postby pErvinalia » Tue Dec 05, 2017 12:25 pm

4. How you even manage to tie your shoelaces in the morning...
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Re: Dumb astrophysics question for clever twats

Postby Tyrannical » Tue Dec 05, 2017 12:31 pm

pErvinalia wrote:4. How you even manage to tie your shoelaces in the morning...


I don't, I wear sandals. And if too much snow, then boots.
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Re: Dumb astrophysics question for clever twats

Postby Rum » Tue Dec 05, 2017 12:35 pm

For me the nub of this is how the universe appears to be the same size when you look out from any point within it. I suspect our puny 3 dimensional (4 at a push) thinking lets us down and there is something very strange going on that maybe maths can describe but probably not ordinary language.
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Re: Dumb astrophysics question for clever twats

Postby Tyrannical » Tue Dec 05, 2017 12:54 pm

Rum wrote:For me the nub of this is how the universe appears to be the same size when you look out from any point within it. I suspect our puny 3 dimensional (4 at a push) thinking let's us down and there is something very strange going on that maybe maths can describe but probably not ordinary language.


I think this is what you mean.
https://en.wikipedia.org/wiki/Cosmic_microwave_background
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Re: Dumb astrophysics question for clever twats

Postby Tero » Tue Dec 05, 2017 1:28 pm



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Re: Dumb astrophysics question for clever twats

Postby JacksSmirkingRevenge » Tue Dec 05, 2017 3:36 pm

Rum wrote:For me the nub of this is how the universe appears to be the same size when you look out from any point within it. I suspect our puny 3 dimensional (4 at a push) thinking lets us down and there is something very strange going on that maybe maths can describe but probably not ordinary language.

I think of it as a sort of inside-out event horizon surrounding the observer. Because space is expanding at an increasing rate, there comes a point where light cannot move fast enough to get to the observer...it just keeps traveling across the space which is stretching away from the observer. Like an ant trying to walk along an infinitely stretchy (but initially short) rubber band.
Disclaimer:- This could be complete bollocks.
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Re: Dumb astrophysics question for clever twats

Postby L'Emmerdeur » Tue Dec 05, 2017 10:34 pm

pErvinalia wrote:If space-time is expanding, they can't be moving further apart, as units of measurement are expanding at the same rate.

I'm sure the theorists are right about this stuff, it's just that I find the pop sci explanations we get from them/magazines really inadequate.


I was writing my last post in this thread rather late in the evening, and my recollection failed me. Should have stuck to finding reputable sources (and reading them thoroughly) for everything I posted!

This --

One way of looking at it is that space-time is expanding, but that would imply that there's something that it's expanding into. Since the Universe is defined as 'everything there is' that hypothetical something is just part of the Universe. Non space-time, but still part of the Universe?


-- isn't an accurate presentation of the current consensus on cosmology. One site that I've found useful over the years is Cornell University's 'Ask an Astronomer'

'Is the universe expanding faster than the speed of light?'
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