distant galaxies, the big bang and relativity

[EternalSceptic]

Hi all,

Yesterday an idea sprang into my mind, while i was lurking through the NASA sites.

Hubble detected several very distant galaxies and supernovae in a distance between 8 and 12 billion lightyears and that raised the following question in my mind:

According to NASA, at least one of these galaxy clusters is (as we see it) just 600 million years old (see http://www.nasa.gov/home/hqnews/2012/jan/HQ_12-007_Hubble_Distant_Protocluster.html) and astronomers are looking for such proto - clusters in all directions.

But if we see these clusters and supernovae in a state where they are just between 500 and 1000 million years old, e. g. 500 t0 1000 million years after the big bang, then they cannot be billions of light years apart (at least when we assume a single point as the origin of the big bang) or

1) The big bang hypothesis needs a thorough rework
or
2) the speed of light in this situation was much higher than c
or
3) my thoughts are noting but a brain fart (The most likely explanation )

Any ideas?

Kind regards
EternalSceptic

Edit: To clarify: if we detect such clusters, say, in opposite directions, then the must have been some 20 billion light years apart 10 billion years ago

 

[BravesFan]

Well it said they came into existence as a cluster only 600 million years after the Big Bang (13.75 billion years ago) so that would make them say 13 billion years old and 12 billion light years away. so we would still have a billion years of light that had made it this far already.

and as such, being 13 billion years old, could have indeed become billions of light years apart as we know that all things are moving away from the center and away from each other .

That's how i interpret the data anyway...some other ,more knowledgable folks may chime in and correct me.

 

[bjornart]

The movement of matter due to the Big Bang is not constrained by the speed of light. It's an expansion of space rather than matter moving. There is nothing wrong with the idea of the currently observable universe being 20+ billion light years across 10 billion years ago. Although I'll leave it to an actual astrophysicist to say if it's accurate, what with accelerated expansion and all.

I can't seem to find a good cite for the size of the universe at different times, except for the "current" size of the observable universe:

"The comoving distance from Earth to the edge of the observable universe is about 14 billion parsecs (46 billion, or 4.6 × 10¹⁰, light years) in any direction." Wikipedia: Observable_universe#Size

 

[Roger Ramjets]

According to the Big Bang theory it wasn't just the matter in the universe that was clumped together, the whole universe itself was compressed into a small space.

As an analogy, imagine inflating a balloon which has dots painted on it. The dots are stuck to the surface and cannot move around, and yet they become further apart as the balloon is inflated. Now imagine a light wave being sent from one dot to another. As the balloon is inflated the light wave continues to travel at the same speed, but the distance it has to go increases, causing the frequency to decrease at the destination dot - red shift!

The Big Bang theory explains certain observations that shouldn't occur if the the universe is static (eg. cosmic microwave background) but it doesn't explain why it's expanding. It has been proposed that it is being forced apart by 'dark energy', whilst 'dark matter' holds the galaxies together. Purportedly this 'dark energy' and 'dark matter' makes up 95% of the universe, with only 5% being normal matter.

I'm no scientist and know little about cosmology, but I wonder whether the Big Bang model might be a bit too simplistic. My WAG is that the universe is actually a huge black hole. Inside a black hole, space 'curves around' to keep everything inside it. As stuff falls into it, so the total amount of matter and energy inside it increases and the hole itself gets larger. That sounds suspiciously like what is happening in our universe. If everything in the universe is inside it, shouldn't it also have an event horizon like a black hole? Is our universe sucking stuff in from outside, and is this what is causing it to expand?

 

[Belz...]

I'm pretty sure your figures are off, EternalSkeptic. But as bjornart said, space expands so the distance between two objects over a long period is not just due to the speed of the things themselves. See "big rip" for an interesting far-future scenario.

 

[Ziggurat]

I'm no scientist and know little about cosmology, but I wonder whether the Big Bang model might be a bit too simplistic. My WAG is that the universe is actually a huge black hole. Inside a black hole, space 'curves around' to keep everything inside it. As stuff falls into it, so the total amount of matter and energy inside it increases and the hole itself gets larger. That sounds suspiciously like what is happening in our universe. If everything in the universe is inside it, shouldn't it also have an event horizon like a black hole? Is our universe sucking stuff in from outside, and is this what is causing it to expand?

The analogy doesn't really work. Once you are inside the event horizon of a black hole, your universe (meaning everything which is simultaneous with you) will only shrink, never expand, even if the event horizon expands. Furthermore, the interior of a black hole is very much not isotropic, but our universe appears to be.

 

[sol invictus]

But if we see these clusters and supernovae in a state where they are just between 500 and 1000 million years old, e. g. 500 t0 1000 million years after the big bang, then they cannot be billions of light years apart (at least when we assume a single point as the origin of the big bang)

The big bang isn't really a "point" in any normal sense of the word. It's the entire universe at a certain time when there's a curvature singularity.

Because it's singular, it's a bit hard to picture. So imagine the universe a tiny fraction of a second later. That universe at that time was, as far as we know, infinite. It had infinite volume, and light signals emitted from one point in it will take arbitrarily long to reach distant parts of it. (The former isn't true in a closed universe, but the latter might be.)

So there's no problem with some galaxies being very far from us when they were young.

 

[Farsight]

Hubble detected several very distant galaxies and supernovae in a distance between 8 and 12 billion lightyears and that raised the following question in my mind: According to NASA, at least one of these galaxy clusters is (as we see it) just 600 million years old ... and astronomers are looking for such proto - clusters in all directions. But if we see these clusters and supernovae in a state where they are just between 500 and 1000 million years old ... then they cannot be billions of light years apart ... or

1) The big bang hypothesis needs a thorough rework
or
2) the speed of light in this situation was much higher than c
or
3) my thoughts are noting but a brain fart (The most likely explanation )

Any ideas?

None of the above! When they say "at a distance of 12 billion light years" they mean the light has been travelling for 12 billion years. While it's been travelling the universe has been expanding. so the true distance is greater than that. Have a look at the observable universe on wiki. If light had been travelling for 13.7 billion years the thing that emitted it is circa 46 billion light years away, so a galaxy "at a distance of 12 billion light years" is really at a distance of about 40 billion light years.

 

[Kwalish Kid]

None of the above! When they say "at a distance of 12 billion light years" they mean the light has been travelling for 12 billion years. While it's been travelling the universe has been expanding. so the true distance is greater than that. Have a look at the observable universe on wiki. If light had been travelling for 13.7 billion years the thing that emitted it is circa 46 billion light years away, so a galaxy "at a distance of 12 billion light years" is really at a distance of about 40 billion light years.

The NASA press release does not use the phrase "at a distance of 12 billion light years". If and astronomer uses this phrase, they are very probably not using the light travel time, given that a light year is a measurement of distance.

 

[edd]

It does seem to be the case that the media uses light travel time distances an awful lot - and while NASA didn't use that exact wording there they do say "Hubble found five tiny galaxies clustered together 13.1 billion light-years away."

 

[Farsight]

And later on the article says "The observations are part of the Brightest of Reionizing Galaxies survey, which uses Hubble's WFC3 to search for the brightest galaxies around 13 billion years ago, when light from the first stars burned off a fog of cold hydrogen in a process called reionization". I've been caught out on this light-travel distance before. I think it's odd that it's so prevalent myself, but such is life.

 

[EternalSceptic]

Thank you all for your input, it gave me a lot to think about.

At the moment i tend to my OP point 3)

Please give me some time to really think it over, I will get back in a day or so

Kind regards

 

[edd]

It's certainly not 3 - it's not in any way a silly question and it's something that's a frequent source of confusion (and hopefully later enlightenment!)

 

[kalen]

This thread has reminded me of a question that I've had for a while.

We can look out in all directions and see very distant objects. Looking out far enough, one will see objects from the early universe. Now, for example, I choose two objects that appear to be 10 Gy away and, from my point of view, are 2 rad (115 deg) apart in the sky. Naively, I would estimate that these objects are separated by a distance of about s=Rxtheta=(10 Gy)(2)=20 Gy. This seems really big if the universe was small a long time ago.

The problem is that from my point of view, as I look farther and farther out, the universe gets younger and younger, but it also gets bigger and bigger.

And the Big Bang predicts that the young universe is more dense than it is today. Do we really see more and more galaxies closer and closer together as we look farther out into space?

 

[edd]

Sort of - there's a bunch of ways of measuring distance. Light travel time is one and angular diameter is another (there's also luminosity and comoving distance - the latter is the 'scaled out' one that gives Farsight's 40 billion figure).
Angular diameter distance is famously not monotonic - after a certain distance things start looking bigger as they get further away and not smaller. So you see fewer galaxies as you look further since the volume is smaller - but each galaxy looks bigger.

 

[CapelDodger]

Angular diameter distance is famously not monotonic ...

For small values of "fame".

 

[edd]

Well yes

 

[kalen]

Sort of - there's a bunch of ways of measuring distance. Light travel time is one and angular diameter is another (there's also luminosity and comoving distance - the latter is the 'scaled out' one that gives Farsight's 40 billion figure).
Angular diameter distance is famously not monotonic - after a certain distance things start looking bigger as they get further away and not smaller. So you see fewer galaxies as you look further since the volume is smaller - but each galaxy looks bigger.

That makes a bit of sense - things looking bigger the farther away they are. I suppose if we were able to look all the way back to the Big Bang, it would have to appear everywhere in the sky.

If distant galaxies look bigger, do they appear brighter, as well?

 

[EternalSceptic]

It's certainly not 3 - it's not in any way a silly question and it's something that's a frequent source of confusion (and hopefully later enlightenment!)

Thank you

Before I proceed i'd like to ask you, to be patient wit my English - it is not my first language. And please don't hesitate to correct me if my grammar or wording is bad. Thank you.

First of all: I am not here to defend an opinion ot "theory". I just want to get a better understanding. So. if something whicht I write, sounds like an assertion, please understand it as a question. And I'd like to proceed to the next step in the discussion only if I am sure, that I have understood and that we agree in the present step

Let me start with what we know for sure.

We know, beyond any reasonable doubt, that the vacuum speed of light relative to its source is constant, no matter how fast the source of light moves. We also know this speed pretty exact (down to cm/second I think)
We also know the "signature" (absolute brightness an spectrum) of Type 1a supernovae from such explosions in "nearby" galaxies.
Furthermore we know, that our Universe is (still) expanding. We know that from the amount of red shift in the spectrum of distant stars and galaxies. And we can, at least roughly, estimate the distance of a supernova using it's relative brightness and the amount of red shift.

Is this so far correct?

 

[Puppycow]

As the balloon is inflated the light wave continues to travel at the same speed, but the distance it has to go increases, causing the frequency to decrease at the destination dot - red shift!

That's something I've been wondering about.

The first time I heard it explained, I heard that the red shift was caused by the distant galaxies moving away from us, but if I understand you correctly, the red shift is actually caused by the expansion of the universe. Or is it both?

I.e, is the wavelength of the light after traveling 1 billion light years through space the same as the wavelength of the same light after traveling 10 billion light years though space when it finally reaches us?