Science Questions

How do we see light from the distant past?

Fri, 24th Jun 2011

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Question

Larry Deck asked:

We are just now seeing light from galaxies that formed a few hundred million years after the big bang.  I would think that a now-distant galaxy we are observing was relatively close to us at the time it formed.  Why are we only now seeing the light from its formation.  Is it because our two galaxies are moving away from each other at a speed close to the speed of light?  Otherwise, I would think that the light from that event would have passed by us long ago.

 

Larry Deck

larrydeck@me.com

 

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Larry Deck asked the Naked Scientists: We are just now seeing light from galaxies that formed a few hundred million years after the big bang.  I would think that a now-distant galaxy we are observing was relatively close to us at the time it formed.  Why are we only now seeing the light from its formation.  Is it because our two galaxies are moving away from each other at a speed close to the speed of light?  Otherwise, I would think that the light from that event would have passed by us long ago. Larry Deck larrydeck@me.com What do you think? Larry Deck, Wed, 1st Jun 2011



Inflation answers this question, I think. Photons, along with the other particles during inflation made sure that the space between objects increased at a speed faster than light, so all the light from our past still has to catch up considerably with the present detector. Mr. Data, Wed, 29th Jun 2011

Hello Larry

Its not only inflation (which tends to be thought of as a short time very soon after the big bang) but expansion.  The universe is getting bigger - space itself is expanding.

When the light was emitted from the first stars the universe was already pretty damn big (this is due to the inflation period) and since then it has continued to grow. So whilst the light has been travelling towards us the distance it must cross has been increasing.

- Basically Yes; the gap between the two galaxies is increasing at a very high rate - the movement through space is small in comparision - because space itself is expanding.  There are galaxies that are so far away that light will never cross the gap between them - the gap gets bigger faster than light.

Mr D - not sure what your second sentence meant.  Inflation and expansion are not driven by photons and particles
imatfaal, Wed, 29th Jun 2011

- Basically Yes; the gap between the two galaxies is increasing at a very high rate - the movement through space is small in comparision - because space itself is expanding.  There are galaxies that are so far away that light will never cross the gap between them - the gap gets bigger faster than light.

Mr D - not sure what your second sentence meant.  Inflation and expansion are not driven by photons and particles



My post said nothing about expansion driven by photons. If you want to know, inflation is driven by particles called Inflatons. And I disagree with your explanation. Expansion of local space in present time is very slow. Very slow next to the speed of light. Inflation played the largest part in the phenomenon the OP speaks of. Mr. Data, Wed, 29th Jun 2011

(also as short as inflation was, you should try and imagine the distances achieved between particles as it was a superluminal phase of the universe). Mr. Data, Wed, 29th Jun 2011



QFT - highlights mine.  'Photons...made sure' - that gives the impression that photons and particle were the cause.

Mr D - after inflationary period the universe was still pretty small (some go as far to say that it was grapefruit sized (!) ; around the time of the era of last scattering it was tens of millions of ly, and by the formation of the first stars it was a couple of billion ly.  As the light has taken 13 billion ly to get to us, I think you are incorrect to write off the effects of expansion. 

The inflaton is highly hypothetical - it is a name given to an unknown phenomenom imatfaal, Wed, 29th Jun 2011



QFT - highlights mine.  'Photons...made sure' - that gives the impression that photons and particle were the cause.

Mr D - after inflationary period the universe was still pretty small (some go as far to say that it was grapefruit sized (!) ; around the time of the era of last scattering it was tens of millions of ly, and by the formation of the first stars it was a couple of billion ly.  As the light has taken 13 billion ly to get to us, I think you are incorrect to write off the effects of expansion. 

The inflaton is highly hypothetical - it is a name given to an unknown phenomenom


Hmmm... yes... it could have been seen in that light. No - light was not the cause, I was speaking very loosely which caused the confusion. I apologize.

''The inflaton is highly hypothetical - it is a name given to an unknown phenomenom.''

Yet we speak so freely of an inflation field yes? Inflation involves temperatures which is at the core of understanding how it is a field with its own elementary particle, where temperatures depend on it's decay processes.

''(some go as far to say that it was grapefruit sized (!) ; around the time of the era of last scattering it was tens of millions of ly, and by the formation of the first stars it was a couple of billion ly.  As the light has taken 13 billion ly to get to us, I think you are incorrect to write off the effects of expansion''

I think you underestimate the inflationary phase of the universe, to be honest. It was a serious rapid expansion, seperating objects by incomprehensible light years - I do not write off expansion, but the serious spaces between galaxies are almost certainly a major part of the superluminal expansion of the universe. Mr. Data, Wed, 29th Jun 2011

Note I said ''during inflation'' in my post. I never said they were responsible. Mr. Data, Wed, 29th Jun 2011

 

The inflationary phase was very short and did not end with seperations of light years
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html
You are confusing inflationary and the early expansionary periods
imatfaal, Wed, 29th Jun 2011

 

The inflationary phase was very short and did not end with seperations of light years
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html
You are confusing inflationary and the early expansionary periods



I'll look into this... but I still think you underestimate the effects. Mr. Data, Wed, 29th Jun 2011

 

The inflationary phase was very short and did not end with seperations of light years
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html
You are confusing inflationary and the early expansionary periods



Right... I've had time to mentally correct this. Inflation had the largest and most impact way to effect distances in spacetime. There was hardly no distance between objects, and also spacetime was highly curved, implying that objects where very close to each other. Inflation flattened space (this alone is enough to calculate the effects of how much space was compensated for in the phase). Mr. Data, Wed, 29th Jun 2011

May I ask who wrote the article: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html ???

it's riddled with mistakes. Mr. Data, Wed, 29th Jun 2011

I will example one from practically the very first sentance:

''Before a time classified as a Planck time, 10-43 seconds, all of the four fundamental forces are presumed to have been unified into one force. All matter, energy, space and time are presumed to have exploded outward from the original singularity. Nothing is known of this period.

Who says we don't know what happened in this period? Inflation caused many particles to decay, due to a ''fine structure'' in the temperature of the universe; in short, many particles decayed, meaning we know the effects during this period in light of QM.

Mr. Data, Wed, 29th Jun 2011



Sorry MrD - you are in a hole and still digging.  Hyperphysics is a well-reknowned physics educational asset written by a professor of physics at georgia state.

THe inflationary period is well after the planck period in which the four forces were unified - the universe was a million or so times older by the time inflation dominated.  imatfaal, Wed, 29th Jun 2011



Sorry MrD - you are in a hole and still digging.  Hyperphysics is a well-reknowned physics educational asset written by a professor of physics at georgia state.

THe inflationary period is well after the planck period in which the four forces were unified - the universe was a million or so times older by the time inflation dominated. 


What hole am I digging exactly? You've shown me no proofs - A dodgy website at best, and to be honest, pulled from an inexperience of inflationary models. Not to mention that I never said that the inflationary period was a pre-state... In fact, this is a subject I have spoke before...??? In this post? Not sure, but I have always been clear it was a post big bang phenom. Mr. Data, Wed, 29th Jun 2011

Not to say also, I seem to understand the reasons for unflation much more clarent than yourself, also to mention I realize the importance of the dynamical temperature changes which imposes the existence of the fundamental particle, the Inflaton.

Don't challenge me, on challenges given by yourself. Explain to me first why I should except your proposal that the inflationary period had less effect on distances than I make out, taking into account it almost flattened spacetime... Your call. Mr. Data, Wed, 29th Jun 2011

Another point... who mentioned hyperphysics? As far as I understand hyperphysics, it involves extra dimensions. It does not answer the questions posed. Just like string theory, your speculations are wavering towards a great misunderstanding of what the inflationary phase did to physics, or matter in the universe in general. Answer please your reasoning. Mr. Data, Wed, 29th Jun 2011

You did in an earlier post where you said "May I ask who wrote the article: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html ??? it's riddled with mistakes."

The emphasis is mine.

Imfataal, is my understanding correct: inflation was a very early phase in the evolution of the universe and though it involved an expansion at greater than light speed, it did not proceed to the point where the universe was thousands or even hundreds of light years across? Therefore the present distances between galaxies and delays on receiving light from distant galaxies is primarily due to expansion? Ophiolite, Wed, 29th Jun 2011

You did in an earlier post where you said "May I ask who wrote the article: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html ??? it's riddled with mistakes."

The emphasis is mine.

Imfataal, is my understanding correct: inflation was a very early phase in the evolution of the universe and though it involved an expansion at greater than light speed, it did not proceed to the point where the universe was thousands or even hundreds of light years across? Therefore the present distances between galaxies and delays on receiving light from distant galaxies is primarily due to expansion?


No I asked who wrote the comments made in the page you sent me to... was that named hyperphysics.... how hyped up!!!!!!! Mr. Data, Wed, 29th Jun 2011

That would be me who posted the link to Hyper-physics.  Hyperphysics is an on-line teaching aid written and kept up to date by Dr Rod Nave who teaches physics and cosmology at GSU.  It is reknowned as a good and correct repository of a huge amount of physics.  imatfaal, Wed, 29th Jun 2011



Really... do you question the postulate I made on one of the pages concerns? Of not, please investigate this, so that if there is any corruption in my data, I can reassess my data bank with new knowledge. As far as I am aware, there are mistakes with this ''other prefessional''. I have a Diploma and Masters in physics. This will be an interesting battle if your source really claims some of the things he does. Mr. Data, Wed, 29th Jun 2011

Imatfaal is right Mr Data, it is the model relying on the standard model of particles. You can look in Wikipedia. But a Bigbang from a singularity is hypothetical or even speculative. CPT ArkAngel, Wed, 29th Jun 2011

Mr D - a discussion of the universe prior to 10-43s would be off topic.  If you wish to claim that much is known, can be tested, and proven about the universe in the planck period open a thread in New Theories. imatfaal, Thu, 30th Jun 2011


The expansion of local space is, and always is, zero. Local space is euclidean. If we speak about small regions, then it depends how big a region we are talking about. On large scales, the expansion of the universe in the current era is definitely superluminal. PhysBang, Thu, 30th Jun 2011

Yeah, nice definition PhysBang. As I see it, the ('superluminiosity 'of 'FTL') does not break the (local) limits defined for our universe, assuming that what we're talking about here doesn't 'expend energy'. We have two states in the universe, expend some energy, and you will meet a barrier defined by lights speed in a vacuum, or rather never come close to it. Don't expend 'energy' and you will now find that a lot of stuff is 'possible', the 'expansion' being one of them. Well, it's how I started to look at it at least. And light can be at 'c' because it in fact is 'uniformly moving' not expending any 'energy'. That is what accelerations is all about, expending energy to break a symmetry, introducing a local asymmetry to the frame the universe represent relative your acceleration.
=

Making our universe a koan of galactic proportions :)
How do you go FTL without expending energy?

Does a tunneling expend 'energy'
Or a entanglement. yor_on, Thu, 30th Jun 2011


The expansion of local space is, and always is, zero. Local space is euclidean. If we speak about small regions, then it depends how big a region we are talking about. On large scales, the expansion of the universe in the current era is definitely superluminal.


When I said local space, I did not mean it in the ''mathematical context'' you have taken it for. I mean it for a general case where we measure the speed in which our own star system is travelling through space. All star systems, and even larger scale structures (in their own local sense) are all travelling through space at different speeds: And as Prof. Hawking assures us in his book ''A brief History of Time'', some of the galaxies are even moving near at the speed of light. This is because of an inhomogeneous spacetime expansion rate which was left in this state from inflation.

You are also wrong in stating that ''On large scales, the expansion of the universe in the current era is definitely superluminal.''

As far as I am aware from the data, only the most distant galaxies are now receeding at a superluminal speed. I don't see any data suggesting that the speed we are moving at measures the same. Mr. Data, Sat, 2nd Jul 2011

Mr Data, the expansion is what does it, there are no objects in space going FTL. But with an expansion acting on space all distances grow, and the further away the faster they will seem to move. It's a very weird way of FTL but, just as PhysBang points out, it will pass FTL for us looking, and those looking back will find us doing the FTL. yor_on, Fri, 15th Jul 2011

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