[Malcolm Ellis]

Malcolm Ellis  asked the Naked Scientists:
   
Hi there,

Here's one that always confuses me.  Light from distant stars takes time to reach us - ie @ the speed of light, C.  

We use this time delay to 'look back in time'  towards the big bang.  But for this to happen would not the universe have had to be expanding quicker than C at least some time in its history to get  'ahead' of the information coming/going to distant areas?

For instance, wouldn't those atoms which make up the Earth have had to have gotten here (for example) 12 billion years before the light from an object 12 billions years ago left its source?  Not just a bit in front of the light wave but 12 billion years earlier?

Ouch! This does my head in...

Regards

Malcolm Ellis
Melbourne
Australia

What do you think?

[Bill S]

Does my head in as well!
Might be worth keeping a watch on the thread "One of the first galaxies to form in the young Universe?" I have just posted a related question there.
Between the two threads we might both get some relief for our heads.   

[Joe L. Ogan]

I think that supposedly being a part of the Big Bang and being able to look back 14 billion years to see it happen puts a question about the existence of the Big Bang Theory.  Thanks for comments.  Joe L. Ogan

[Murchie85]

Yes this is a mind melter indeed,

Firstly the universe has expanded faster than the speed of light (according to the most accepted view anyway). The time when expansion was at its fastest was a period called inflation.

We can only see back as far as aproximatly 13.75 billion years which tells us the known universe (i.e that which we can see) must be that big in radius. This does not mean the universe is that big in reality.Thanks to hubble we know that the universe is expanding and has done at an accelerating pace and its much bigger than the known size estimated by speed of light, therefore the space must have expanded faster than the speed of light.

At first glance this may appear to break some fundamental laws but its not matter thats moving that fast, just the space inbetween. So stars that are more distant than 14 billion light years may or may not be there but we have know way of telling at present as their light has not yet had enough time to reach us.

Hope this helps

[chris]

The point that's being made is that for us out here to be seeing the light that left that early galaxy 13 billion light years ago implies that the light has been travelling towards us ever since.

So, given that the galaxy in question pre-dates our own and was around just after the Big Bang (relatively speaking), why are we here before the light from that early galaxy? i.e. how did the matter get here before the light did?

This implies extremely fast inflation of the young Universe.

Chris

[Vereava]

Yes this is a mind melter indeed,

Firstly the universe has expanded faster than the speed of light (according to the most accepted view anyway). The time when expansion was at its fastest was a period called inflation.

We can only see back as far as aproximatly 13.75 billion years which tells us the known universe (i.e that which we can see) must be that big in radius. This does not mean the universe is that big in reality.Thanks to hubble we know that the universe is expanding and has done at an accelerating pace and its much bigger than the known size estimated by speed of light, therefore the space must have expanded faster than the speed of light.

At first glance this may appear to break some fundamental laws but its not matter thats moving that fast, just the space inbetween. So stars that are more distant than 14 billion light years may or may not be there but we have know way of telling at present as their light has not yet had enough time to reach us.

Hope this helps

Almost sounds as if the universe is rendering existence the same way a video game renders the levels/maps

Also, Chris, what if the universe has always been and we just popped out of the super massive black hole at the center of our galaxy? Doesn't matter shoot out of black holes? If I were to guess, I'd imagine that's how galaxies are formed (though who knows)

[CliffordK]

Remember, all of this is talking about a radius.

So...
From Earth, we can see in all directions a little over 13 billion light years, or a total of about 26 billion light years across.

Wikipedia gives this diagram.
http://en.wikipedia.org/wiki/UDFy-38135539
(apparently a NASA image: http://www.nasa.gov/images/content/56534main_hubble_diagram.jpg)


Anyway, it shows a representation of what we can see of the Big Bang as a sphere around Earth.

So, for us to see a sphere around the earth of approximately 26 billion light years.

The Universe had to have expanded to a size of at least 26 billion light years in size by at least 13 billion years ago.

So, if we believe that the universe existed as a point-source less than 14 billion years ago, then that point source would have had to expand to at least 26 billion light years in diameter within the first billion years. 

However, if it was expanding at "faster than light", then it would have had to slow down to normal light speed for us to see it.  That just seems like a lot of expansion, as well as mysterious slowing without explanation.

And, of course, we don't know what is beyond the 26 billion (or so) light year universe sphere that we can see (other than assuming that it is bigger now).

[CPT ArkAngel]

Perhaps, our Universe is much older than 13 billion years... around 27 billions years? Or it would mean light is travelling instantly... [V]

[QuantumClue]

Remember, all of this is talking about a radius.

So...
From Earth, we can see in all directions a little over 13 billion light years, or a total of about 26 billion light years across.

Wikipedia gives this diagram.
http://en.wikipedia.org/wiki/UDFy-38135539
(apparently a NASA image: http://www.nasa.gov/images/content/56534main_hubble_diagram.jpg)


Anyway, it shows a representation of what we can see of the Big Bang as a sphere around Earth.

So, for us to see a sphere around the earth of approximately 26 billion light years.

The Universe had to have expanded to a size of at least 26 billion light years in size by at least 13 billion years ago.

So, if we believe that the universe existed as a point-source less than 14 billion years ago, then that point source would have had to expand to at least 26 billion light years in diameter within the first billion years. 

However, if it was expanding at "faster than light", then it would have had to slow down to normal light speed for us to see it.  That just seems like a lot of expansion, as well as mysterious slowing without explanation.

And, of course, we don't know what is beyond the 26 billion (or so) light year universe sphere that we can see (other than assuming that it is bigger now).

There should be some dark space after that radiation era. The big bang was quite silent of energy and matter for a good while. I think on the scale of around 300,000 years.

[QuantumClue]

Or is that what the dark ages here are supposed to represent? I like the idea how the author has used radiation to express how the big bang arose. That much is nice, but I think they have the dark ages mixed up. In the beginning, there was nothing, for many many years, until light emerged when the universe had grew considerably old. Should the dark ages not be before the radiation field... or ''after'' the radiation field in the diagram?

[imatfaal]

QC The radiation era is not exactly at the big bang - but it is the effects.  Whilst the universe was cooling down after big bang, inflation, reheating, etc it was hot enough that the entire universe was filled with light emitting plasma. During this first 400,000 years or so the universe was opaque and uniformly brilliant with light.  As plasma interacts with EMR all light was scattered or absorbed - as the universe cooled and atoms formed then the universe stopped scattering/absorbing - poetically known as the era of last scattering.  The last remnants of this light (the surface of last scattering) - the light that was given off by the plasma but managed to remain un-absorbed - is what we can now see as the CMBR.  The dark ages are the period between the last light generation by plasma and the first light generation by stars - it is basically the period during which the first stars formed

[Bill S]

So, if we believe that the universe existed as a point-source less than 14 billion years ago, then that So, if we believe that the universe existed as a point-source less than 14 billion years ago, then that point source would have had to expand to at least 26 billion light years in diameter within the first billion years.  .

No problem with this.  What I have been struggling for some time to get my head around is this:  If the galaxies were very much closer together 13 billion LY ago, and we are seeing galaxies that are 13 billion LY away as (and presumably where) they were 13 billion years ago, why do we see them 26 billion LY apart now?

Does this mean that they were 26 billion LY apart 13 billion years age?  Is this what you are inferring when you say that the "point source would have had to expand to at least 26 billion light years in diameter within the first billion years"?   

[imatfaal]

Bill - I am not sure of Clifford's explanation, having trouble reconciling it. Inter alia;

From Earth, we can see in all directions a little over 13 billion light years, or a total of about 26 billion light years across.

No.  We can see things from which the light has travelled for 13+billion years - but as space itself has expanded during this period the actual distance of these objects is much greater.  As an example the last glow of the big bang is still visible in every direction - it is now red-shifted down to microwaves,  it is the Cosmic Microwave Background Radiation.  This light we observed now has been travelling towards us for 13.3ish billion years.  But the expansion of the universe means that the area which originally emitted this radiation is now 46+ billion lightyears away!

Even though it is light that is travelling:  'Lightyears away' ≠ 'Years old' in our expanding universe

That is the current limit of the observable universe; 13.3ish billion years or 46ish billion light years. Earlier than this the entire universe was hot plasma and all emitted radiation was rapidly absorbed and scattered as plasma is opaque.  However, plasma is not opaque to neutrinos and gravity waves - and once we can get a handle on how to detect and utilise these methods, we may be able to probe the universes earlier days before the era of last scattering (I love that phrase - who says physicists aren't poetic)

[yor_on]

It's a weird idea isn't it? That the universe is expanding. But if it does maybe this is the way it got created too. then every point in our universe 'creates' or 'begets' more points in and around it, a little like spheres constantly growing on spheres growing on.. and with every point being the seed, including the new points possibly. If it was so it seems to me expansion must accelerate. When it comes to age as compared to its possible size? I think Imatfaal is right, although if we consider light as a wave, propagating in a space/vacuum that constantly grows it has to become 'stretched'. If it does it should to us look like a red-shift as it becomes 'weaker'. There has to be a limit somewhere for where a red-shift becomes impossible to measure for us, so I don't dare to guess how big a universe it is by the time that 'weakest' light will reach us. But it seems some have And it's possible, the theory is at least agreeing with the facts known.

An early inflation 'FTL' and subsequent expansion might also be explain able the same way. Consider a plasma universe cooling, isotropically, evenly, filled with particles. Then let there be stress-faults developing in it where 'space' suddenly 'inflates'. That might give us the mass distribution we see and it's a nice way of making space 'move' as seen from us, or any point in space, faster than light after enough new points been created between you and what you look at. None of those points coming to be in their self need to break any light-speed in their appearance as I see it. It's the pure amount of them constantly coming to be that makes all points in the universe 'move away' from each other. That the galaxies themselves won't 'expand' is explainable through gravity. It seems to be able negate the expansion, there you have two choices as i see it. Either one can assume that the 'expansion' takes place inside the galaxies too and that gravity constantly rectify those points by keeping all objects of matter 'the same' relative each other. The other is that gravity in fact somehow annuls a expansion if of sufficient 'degree'. Myself I would guess on the first one and then also point out that classically space contains nothing at all, except 'distance', and where gravity and our other EM, strong, weak, nuclear, forces etc works a 'nothing' never comes to be.

The real question might be how space creates a 'distance'.

[AuToFiRE]

I believe that as humans, we are still very primitive and only believe in what we can see and physically manipulate, like light, but i feel there is more to the omniverse than what there appears to be, i believe light isnt the fastest speed there is, we only choose to believe it is

[Geezer]

I believe that as humans, we are still very primitive and only believe in what we can see and physically manipulate, like light, but i feel there is more to the omniverse than what there appears to be, i believe light isnt the fastest speed there is, we only choose to believe it is

You certainly can believe that if you want to, but I think you'll have a hard time convincing many scientists that c is not the limit.

[Bill S]

'Lightyears away' ≠ 'Years old' in our expanding universe

Even in a static universe this would be true, unless the emitting object suddenly appeared, in which case we might reasonably assume it had just started emitting light.

[AuToFiRE]

I believe that as humans, we are still very primitive and only believe in what we can see and physically manipulate, like light, but i feel there is more to the omniverse than what there appears to be, i believe light isnt the fastest speed there is, we only choose to believe it is

You certainly can believe that if you want to, but I think you'll have a hard time convincing many scientists that c is not the limit.

Think of quantum physics for instance, some of the things we once thought was impossible have been done in the realm of quantum physics, we are arrogant to think we know everything there is about physics and the omniverse

[yor_on]

On the other hand, there's still some things we haven't done, although predicted ages ago. Like falling over the edge

[Geezer]

I believe that as humans, we are still very primitive and only believe in what we can see and physically manipulate, like light, but i feel there is more to the omniverse than what there appears to be, i believe light isnt the fastest speed there is, we only choose to believe it is

You certainly can believe that if you want to, but I think you'll have a hard time convincing many scientists that c is not the limit.

Quite so, but it's only arr

I believe that as humans, we are still very primitive and only believe in what we can see and physically manipulate, like light, but i feel there is more to the omniverse than what there appears to be, i believe light isnt the fastest speed there is, we only choose to believe it is

You certainly can believe that if you want to, but I think you'll have a hard time convincing many scientists that c is not the limit.

Think of quantum physics for instance, some of the things we once thought was impossible have been done in the realm of quantum physics, we are arrogant to think we know everything there is about physics and the omniverse

Think of quantum physics for instance, some of the things we once thought was impossible have been done in the realm of quantum physics, we are arrogant to think we know everything there is about physics and the omniverse

I agree. It would be extremely arrogant for physicists to attempt to explain quantum effects without presenting a theory to support their conjecture, but I think they did.