Looking Back In Time ?

[modeller]

We are told that we can look back in time, but can we really ? e.g. looking at a star that is say 2 light years away today, but if I look back next month. I would not be 'seeing' the same thing. It may still be two light years away but both we and it are both one month older in real time.

The light from our own sun takes 8 minutes to reach us but wa can't see what it was like say 20 minutes ago , so we are not really looking back in time . The same with the moon we can't see what is was like even a minute ago.

Yesterday it was said we can now see what it was like a fraction of a second after the big bang but that image has long gone past us and can never be seen again. What have I got wrong ?

[VHG]

The light from a star 2 light years away has taken 2 light years to get here.

So you are seeing the light as it was 2 light years away, in the past.

A probe sent into deep space is seeing the universe as it WAS millions of years ago.

[VHG]

In fact it could be argued EVERYTHING we see is in the past.

Light takes time to get to our eyes, so even if we see something close to us happening, is was a fraction of a second ago (due to the time light takes to get to us).

So looking at things further away just magnifies that time.

So if you look at the sun you are seeing it as it was 8 minutes ago, not NOW.

Look at stars in other galaxies and you are seeing it as it was millions of years ago.

[jim360]

It's one of those where the language is confusing. You are looking "back in time" in one sense, but not in another. Everything we see is an image of how things were in the past, but at a fixed point in the past. Where the time is determined by how far away the object is. We can't look back in time however far we choose for any particular object, no.

[modeller]

So for them to say they could see the universe a fraction of a second after the big bang is nonsense. !

[LazyGun]

Eh? Not sure quite how you arrive at that conclusion Modeller

[jim360]

No, that much is still true - sort of. I thought it was closer to 3 minutes. Becuase just after the big bang the universe was still "tiny", its traces are all over the place, so we can still see it. Things get messier near that sort of time because of the fact that space and time are linked. Beyond that it's outside my area of expertise (such as it is), but anyway we can still see stuff from just after the big bang.

[chaptazbru]

It's fascinating stuff though, isn't it ...?

[modeller]

Well it seems to me if it took 14 billion years to get here , then how can we tell we caught that exact point of time to see . Had we been checking a minute later it would have already passed us by. W

[modeller]

What would happen if I had access to the equipment today ? Would I be able to see that event, bearing in mind that image has already gone past the earth and on into space. Don't you think it strange that that event after 14 billion light years just happened as our researchers were there at that opportune moment.

Recently a scientist said he only once in his life was he lucky enough to be on duty when he saw the birth of a star.

So for these others who saw the birth of the universe an event that has just reached us after 14 billion light years is a bit more than luck.
The only way I could see it tomorrow is if we are moving away from the location of the event at the same speed it is coming towards us.

[factor-fiction]

I think there's a misunderstanding on your part about all of this. The further you look the longer that light has taken to reach us. If I look today I may be able to see at the farthest point what was happening 14 billion years ago. If I look again tomorrow I will be able to see what was happening 14 billion years plus one day ago

[jim360]

Even that;s not quite right factor.

The Big Bang made this Universe. It was such a violent event that traces of it were thrown across the Universe. But the Universe then was small, tiny. So it's as if that event of the past is woven into the very fabric of Space. It's not really that an event happened 14 billion light years away and we are only just see it. The event happened everywhere. "right next" to us and at "the other side" of the Universe. We have been moving away from it, not so much in space but in time. And it has been moving with us, decaying slowly, turning from light into Microwaves as time passes and the energy fades.

Stars nearby do sort of behave in the way factor is describing. We are watching their life a few years behind. A sort of "cosmic lag". The birth of the Universe is too far back to be so simply described, relativity effects start playing a major role.

[factor-fiction]

Maybe, jim360: I don't pretend to understand the big bang timing calculations- I was just trying to address modeller's point that as each day passes the furthest point we can see back will also move forward by a day.
These things make by brain hurt though.

[modeller]

My last tongue in cheek suggestion is obviously not correct, when we are told many of the stars we see are not actually there, they have already burnt up and in time they will not be seen when the light from them ceases. So we are not moving away at the same time as the signal is arriving. If we were the starlight would not go out.

My guess for my original question is that we are assuming a set of radiation conditions that would exist at various times after the big bang and if we find them that ' proves ' we are right, but the whole story is suspect, especially the one two hundrenth of second part.

[Old_Geezer]

The difference is still 2 years between what happened and what is seen, regardless that both star annd viewer progress through time at the same speed (given the usual assumptions).

In affect we do look back in time, we merely can not dicate how far back at the time of viewing, it is a set period.

The issue of looking back at the big bang is similar but different. There we are seeing the affect of that evet in the cosmic radiation and learning/confirming what must have been the case back then.

[jim360]

It is fairly suspect, that figure. Where did you get it from or hear it, do you know?

Even my "3 minutes" is some way off the mark. The CMB is to my knowledge the furthest back we can see at the moment, and that was ~400,000 years after the Big Bang.

In the future we may be able to see further, using new techniques such as neutrino observation or gravitational waves, but the second is still only theory and the first is a way off.

[modeller]

jim //If I look again tomorrow I will be able to see what was happening 14 billion years plus one day ago //
Surely that can't be right ? The physical distance hasn't changed so the length of time can't have changed. One day later would be seen as one day later at the source of the event . The event I saw yesterday has gone for ever.
If there was an explosion on our sun and if I was using a telescope I could have seen it say at the moment it occurred . However in 8 minutes time I could see that explosion again with the naked eye but then it would be gone for good . No telescope , no matter how powerful is ever going to see that explosion again.
The same thing with the big bang , its image is going to be seen by an observer somewhere but once past the observer it can not be seen again , from that position. No matter what telescope you use.

If I went to the sun I might see the result of the explosion.
If I went to the source of the big bang I might see the result .
In neither case would I see the event. Have I missed something ?

[modeller]

jim 360 This may help :
http://www.guardian.co.uk/science/2013/mar/21/planck-telescope-light-big-bang-universe

[modeller]

I can't find the link which said we can see what happened a fraction of a second after the big bang but the abve site helps to find where the report came from.

[jim360]

A telescope would see the image at the same time as you did with the naked eye - only bigger, or clearer. A telescope doesn't change the time of the image being viewed. The Big Bang is different because in a weird and twisted sense it sort of happened everywhere, and everyquote[when], at once. So there's no fixed time when you can look back and say "Oh, look, there goes the Big Bang - and, it's gone". The analogy is closer to thinking of the Big Bang as a picture we are walking away from. No matter how far away we are, the picture stays in the same place with the same image. The analogy isn't perfect but it's not a "blink at you missed it" thing.

[jomifl]

It could be said ( and many will disagree ) that time travels at the speed of light, at least in a practical sense since nothing can travel faster than light (including gravitational effects). That is to say that the earth is attracted gravitationally to where the sun appears to be, not where some would argue it really is. Confusing isn't it?