How can we receive light from an object older than the universe

[Alan McDougall]

Greetings people,

 

Some quasars are believed to be 14 billion light years from us and receding at greater than the speed of light.

 

I still can’t rap my silly little brain around this, how are we earthling sitting out here somewhere in the universe observing light from an object that might no longer exist.

 

The 14 billion light year distance seems impossibility to little me

 

Please help this little tiny entity

 

Take Care

 

ALAN

[swansont]

Is the issue the time it takes (i.e. the light is very old), or the fact that the recessional speed exceeds c?

[Martin]

Hi Alan, Swansont

 

Alan, Swansont is a good one for you to be talking to about this so I won't interrupt. Just letting you know there are others around too. I'm also curious about the same thing he asked? what is the puzzle, as you see it?

==========

EDIT: added on a day later when it seemed Alan wasn't going to reply.

 

Alan,

you seem to have vanished. to learn you have to be persistent about asking questions. maybe you found somewhere else to ask, which is fine.

 

Just for completeness, one of us should respond. Alan asks:

How can we receive light from an object older than the universe?

 

I would reply this way. We DON'T receive light from objects older than the universe---or the 13.7 billion years it has been expanding.

 

the oldest stuff we are currently seeing is stuff that emitted the cosmic microwave background when expansion had already gone on for about 380,000 years. So that stuff is a little bit LESS than 13.7 billion years old.

 

because of the increase in distances, that stuff whose strongly redshifted light we are now receiving as CMB is now about 45 billion LY away from us.

 

that is perfectly natural. When it emitted the light that is now reaching us it was much much closer to us, but distances between things increase over time by Hubble Law. So now it is 45 billion LY away. Big deal.

 

When people first hear this they sometimes have a confused reaction and they say WHAAA! That stuff we are getting light from is now 45 billion LY distant from us! How did the light ever get here in the whole age of the universe!!!???

 

, the 45 billion LY is partly the result of expansion, the light did not have to make the the whole way on its own. some of the distance it had already covered then proceeded to increase.

 

If you are still puzzled by this, keep asking. Someone will explain, maybe by talking about the balloon analogy. but it wouldn't make sense unless you are around and pressing for more explanation. Keep at it and good luck with your conundrum

Edited October 2, 2008 by Martin
multiple post merged

[north]

Hi Alan, Swansont

 

Alan, Swansont is a good one for you to be talking to about this so I won't interrupt. Just letting you know there are others around too. I'm also curious about the same thing he asked? what is the puzzle, as you see it?

==========

EDIT: added on a day later when it seemed Alan wasn't going to reply.

 

Alan,

you seem to have vanished. to learn you have to be persistent about asking questions. maybe you found somewhere else to ask, which is fine.

 

Just for completeness, one of us should respond. Alan asks:

How can we receive light from an object older than the universe?

 

I would reply this way. We DON'T receive light from objects older than the universe---or the 13.7 billion years it has been expanding.

 

the oldest stuff we are currently seeing is stuff that emitted the cosmic microwave background when expansion had already gone on for about 380,000 years. So that stuff is a little bit LESS than 13.7 billion years old.

 

because of the increase in distances, that stuff whose strongly redshifted light we are now receiving as CMB is now about 45 billion LY away from us.

 

wow, geez guy you have to explain this further

 

I mean I have never heard of this 45 billion LY before

 

that is perfectly natural. When it emitted the light that is now reaching us it was much much closer to us, but distances between things increase over time by Hubble Law. So now it is 45 billion LY away. Big deal.

 

why is this perfectly natural ?

 

When people first hear this they sometimes have a confused reaction and they say WHAAA! That stuff we are getting light from is now 45 billion LY distant from us! How did the light ever get here in the whole age of the universe!!!???

 

of course

 

, the 45 billion LY is partly the result of expansion, the light did not have to make the the whole way on its own. some of the distance it had already covered then proceeded to increase.

 

does this make sense though ?

 

or do you want it to make sense ? to fit the BB theory ?

 

 

If you are still puzzled by this, keep asking. Someone will explain, maybe by talking about the balloon analogy. but it wouldn't make sense unless you are around and pressing for more explanation. Keep at it and good luck with your conundrum

 

I'm asking

[Martin]

I'm asking

 

Good. The initial poster Alan went away and didnt keep asking so it wouldn't have been worthwhile writing more explanation.

 

There are various ways to explain this, no telling what will work for you. So I will try something at random. First get up these two Ned Wright animations that show a simplified universe imagined as dots painted on the surface of a sphere. The dots stand for galaxies. they stay still (always at same longitude and latitude) while photons wriggle across the surface. while that is happening the sphere expands.

http://www.astro.ucla.edu/~wright/balloon0.html

 

as the sphere expands by a factor of four, the wavelengths of the photons is stretched out by the same factor. you can see them change color (it is false color just meant to remind you of redshift, they get redder as their wavelength stretches out.

 

even though the galaxies are stationary, the distances between them increase. that's called recession speed, it is not a real speed, each galaxy thinks it is standing still, the photons in the space around it go past it at the usual speed, the speed light always goes.

 

now imagine that you are living on one of those galaxies and at some point in the past you sent out a flash of light, one of those photons in fact, that you see. after a while has past, that photon is farther away from you than you might have expected because it is covering ground at the usual speed of light, but also whatever distance it has already gone is expanding according to the usual percentage rate of hubble law.

 

after you have watched a few times and thought about it, please get back to me. does it make more sense now that back when the universe was a few 100,000 years old (not even a million) the matter that would eventually condense to make the sun and planets sent out some photons and that those photons are now 45 billion lightyears distant from us?

 

in effect expansion leverages whatever distance the light manages to cover on its own.

 

this one is a bit prettier but takes longer to watch---eventually does a big crunch

http://www.astro.ucla.edu/~wright/Balloon2.html

 

fine to keep on asking questions, swansont or I or somebody else will probably reply

Edited October 6, 2008 by Martin

[north]

Martin

 

what does this statement mean ;

 

"the galaxies do not expand: bound systems are not affected by the expansion of the Universe. Also note that the speed of light relative to the nearby galaxies is a constant

 

(I'm more interested in the explaination of the statement in bold )

[Martin]

Martin

 

what does this statement mean ;

 

"the galaxies do not expand: bound systems are not affected by the expansion of the Universe. Also note that the speed of light relative to the nearby galaxies is a constant

 

(I'm more interested in the explaination of the statement in bold )

 

North, when you quote someone, it helps if you say who you are quoting and give a link.

In your post, I at first thought you were quoting me, and I went looking back to see where I had said that.

then I guessed that you might be quoting Ned Wright, but in which of the two places? I had posted two links to Wright pages.

So I went looking on this page:

http://www.astro.ucla.edu/~wright/Balloon2.html

but didn't find the exact quote.

 

Finally I found the quote on this page:

http://www.astro.ucla.edu/~wright/balloon0.html

 

what don't you understand about the two sentences you quoted?

 

Let's take the one you said you were more interested in:

"Also note that the speed of light relative to the nearby galaxies is a constant."

 

What is unclear about this statement?

Edited October 6, 2008 by Martin

[saturn5]

maybe the math is wrong , can it be?

[iNow]

maybe the math is wrong , can it be?

 

Can you please elaborate on your point? Which math? Wrong how?

[interstellar]

RE: How can we receive light from an object older than the universe. Another interesting point is these quasars on the edge of the universe can move faster because they are riding the shockwave of the big bang and because they are at the edge of the universe the gravitation of the rest of the mass of the universe has less influence on them. Like being on earth you weigh more in death valley than you do on top of mount everest.

[Royston]

RE: How can we receive light from an object older than the universe. Another interesting point is these quasars on the edge of the universe can move faster because they are riding the shockwave of the big bang and because they are at the edge of the universe the gravitation of the rest of the mass of the universe has less influence on them. Like being on earth you weigh more in death valley than you do on top of mount everest.

 

Do you have any references for this, because there's a number of flaws with what you stated.

 

For a start the Universe doesn't have an edge, whatever the shape of the Universe turns out to be, neither of the three possible models e.g spatially infinite has an edge involved.

 

Shockwave of the big bang ? Can you elaborate please.

 

Also, the Universe is isotropic, i.e very distance galaxies will be receeding faster, the further away they are from the observer. This holds true for any position you care to pick in the Universe. Stating that the mass of the Universe is somehow concentrated in the centre (there's no centre of the Universe either) and that's why objects far away from the centre are receeding quickly, is just wrong. There's no such thing as absolute space, which would be required for your statement to hold true.

[Riogho]

Slow down there snail

 

I thought the edge of the universe was expanding? How can the universe not have an edge if at once it was nothing? I'm not saying you're wrong, I'm saying I don't understand.

[Martin]

Slow down there snail

 

I thought the edge of the universe was expanding? How can the universe not have an edge if at once it was nothing? I'm not saying you're wrong, I'm saying I don't understand.

 

Riogho, what you say you don't understand is the standard model of cosmology.

1. The standard model doesn't have an edge. In particular it does not have an expanding edge.

2. The standard model doesn't talk about the universe at one time being nothing.

(It leaves unresolved the issue of what the universe was like at the moment expansion started---there are several viable models and observations will be needed to rule some out. At this point there is no scientific reason to believe that there was some sort of nothing right before the big bang. We don't know that.)

 

This thread isn't the place to argue that the standard model is wrong (or right). It is simply the one astronomers (virtually 100 percent) use, with minor variations. We have an educational function to present the standard picture correctly and answer questions about it.

There are some good practical reasons they use it (excellent fit to a huge mass of data, simpler than anything else that fits, consistency with the tested GR theory of gravitation, ease of calculation,...)

 

The points Snail made are all correct in that context.

 

It's possible that Interstellar was trying to tell us about his own personal theory of the cosmos. In that case what I'm saying doesn't apply. But I don't think he was. I think he was trying to say something about the standard picture---the generally accepted view that astronomers have developed. If he was, then Interstellar got several things wrong, and Snail put them right.

 

If you want to get more familiar with mainstream cosmology (I recommend it, it's really interesting!) here's a well-written outreach website

 

Einstein Online

http://www.einstein-online.info/en/spotlights/cosmology/index.html

Also check out the Charley SciAm article in my sig, it is excellent.

Ask questions about anything you read and don't understand---we'll try to respond.