Looking back in time

[BertiWooster]

With the hubble telescope we are able to look back in time to events that occurred billions of years ago , towards the time of the big bang .

My question is should'nt the light have dissapeared a long time ago - how come the light is only just reaching us - where has it been , given that our galaxy would have been created long after the bang .

Where has the light been ' travelling from ' to only just be reaching us now ?

I hope someone understands what i'm trying to ask , and can provide an 'idiot' proof explanation .

Thanks

[Clanad]

Your question should generate several answers... but, I believe the general consensus is that the Universe is somewhere between 13.5 to 15 billion years old. Additionally, quantum physics can only approximate the event of the actual Big Bang.. that is, limitations of predictive theory gets us back to several billionths of trillinonths of a second (Planck Time or distance) after the event. However, again the speculation seems to be inthe direction that within about that speck of time the baby universe inflated from the size of, say a basketball, to the size of our galaxy in a speed far beyond the speed of light... and continues to expand at an extremely high speed. But for the first 200 million years or so, there was little if any organization in the mass of energy that would age into the universe and especially the first or proto stars. Those were fairly short lived, for a number of reasons, but the light that emanated from their short lives travels at the speed of light for infinity or near infinity, since the universe is demonstrably not infinite. So... long winded way of saying the light that is now being observed (actually, measured) has been travelling unimagineable distances and is only now reaching us. The fact that the source of that light has since ceased to exist doesn't matter... think of turning off your hall light at the switch... the light that was on continues to travel, except in the case of the hall light, most of the photons are being absorbed by the house structure, just as much of the original starlight has been absorbed by dust, gas, and galaxies as it has traveled.
Contd.

[Clanad]

Contd.

By the way, there is a segment of the astrophysicist community that proposes a theory that light can "wear out" or grow tired... and eventually cease to be detected... but most of the proponents don't like the implications of the Big Bang Theory and seek to develop a theory that would not require a beginning of space time... but that's another story...
Thanks for asking!

[factor-fiction]

Think of what happens with sound. Sound travels at 300 metres a second. So if there is lan explosion 3000 metres away you hear the sound 10 seconds after it occurred.

Light travels at 186000 miles a second. If you are looking at something 186,000 miles away you see it as it looked a second earlier. When we see the sun which is 93 million miles away we see it as it was 8 minutes earlier. When we see a star with the naked eye we are seeing it as it was many years ago. If you had a fantastic telescope and are looking at something 186 billion (186,000 million) miles away you see it as it was a million years ago

[BertiWooster]

Thanks guys - I did know that for example, the light from the sun takes approx 8 mins to reach the earth - so when we look at the sun we are observing it , the way it was 8 mins ago .

What I didn't know was that in the first billionths of trillionths of a second of the big bang , the universe expanded to an enormous size , far outstripping the speed of the light from the event

So am I correct in saying that :-

1. Our earth has had the time to be in existence for billions of years , because of the initial hugh expansion ; before the light from the initial or near the initial event , has had the time to reach us ?

2. The reason we cant see back to the initial event is that the light would have already past us ?
If we had the technology thousand of years ago , like the Hubble telescope , we would be able to see much nearer to the big bang ?

[mibn2cweus]

First off, no answer is fool proof. You just have to learn to be smarter than the question . This always takes some time and thought in proportion to how smart you are to begin with and what you already know. With that said perhaps the following explanation will help get you started and on your way to understanding the answer.

The universe is both very big and very old, and is in fact believed to be many times bigger now, than the time it has existed would have allowed it to grow, even at the velocity of light. This is possible because the space between objects has itself increased and within a cosmic scale has grown faster than light. However this is more than you need to know to understand how light from the early universe can just now be reaching us.

The light that we observe now originated from a distance equal to the velocity of light. For example, when we look at the Sun, (not the smartest thing to do as you are probably already well aware), we see the Sun, not where it actually is but where it was about 8 minutes ago. This is because it appears to be where it was when the light from it began its journey and that's how long it took the light to get here.

A star that is a thousand light years away appears to be where it was a thousand years ago even though it has in that time been moving to where it actually is now, to the position it will appear a thousand years from now, (if you then know where to look and you live that long).

cont . . .

[mibn2cweus]

Likewise a galaxy a million light years away appears to be (and actually was) where it was then.
The further away a source of light originated, the further back in time that light began it journey to the point in space we are now witnessing it from. So the simplest explanation, although not necessarily completely satisfying, (let alone fool proof) is that we are now at a position in space aligned with and at the right distance to see the light that originated from a point in space the same distance in light years from where we are now, arriving to where we are now.

Now the bad news . . .

For the first hundreds of millions of years following the Big Bang event itself the initial light was reabsorbed in the dense soup of particles that existed at that time. This is analogous to the light we see emitted from the Sun. Sunlight is light energy liberated from the Sun�s surface that following its origins in the fusion process deep within its core was absorbed and reemitted countless times during its migration to the surface, a process which takes millions of years.

So we have the big bang, then the initial expansion and cooling that allowed the formation of elements to take place, the distribution and grouping of these elements that provided spaces between which light could finally travel without being reabsorbed (the afterglow of the big bang) and finally the birth of the first stars and galaxies some of whose light we are just now beginning to see from those which are at the appropriate distance for us through telescopes now capable of seeing them from the vast distances required for their light to just now be reaching us.

cont . . .

[mibn2cweus]

At this point it should be becoming clear that your question is a bit more complicated than it appears on the surface. Here�s some more information on cosmic evolution and the sources of first light.

If you fell asleep while reading this, I can assure you you�re not alone, I did while writing it which is why it took so long and why much of it is a virtual repeat of previous/subsequent answers. Not to suggest that yours are not fascinating and intriguing question�s we are only just now achieving the capability to provide answers to!

[ACtheTROLL]

I suppose then .... in general terms ... it's all relative?

[mibn2cweus]

ACtheTROLL, That sounds like something Uncle Albert would have said.

[BertiWooster]

ooook , tackling this subject at this ungodly hour of the morning is perhaps not the smartest thing to do .
I shall have another read at a more civilised hour .

However , for the avoidance of doubt ; am I correct in saying that my statements in 1 & 2 above are , totally incorrect ?

[mibn2cweus]

1. Although the earliest available light is fading, since the universe is much larger than the distance required for that light to travel, some part of it will always be arriving to our destination.

2. There is a limit to how far back we can see because the light from the original event was consumed (repeatedly absorbed and reemitted) within the extreme heat and density of the event as it unfolded throughout the first millions of years immediately following the event. Kind of like trying to see the fusion reaction within the Sun which is obscured by the slow migration of light out from the core. We are blinded by the emerging altered light as well as by the intervening particles.

I might like to come back and dig this hole a little deeper with your permission but for now I must deal with my immediate future . . .

[beso]

Photons of light persist indefinitely unless they are absorbed. If light travels through a true vacuum it will travel for ever. A perfectly columnated beam of light (an ideal laser) loses no intensity.

However a point source of light radiates out on a spherical front so the original number of photons become more and more spread out and so appear dimmer. That is why you need a telescope to collect enough photons to form a visible image.

One of the weirf things is the distance the light has to travel keeps getting longer during the journey because the space itself that it is travelling through is expanding. This makes the wavelength get longer.

Incidentally the current best estimate of the age of the Universe is now 13.73 billion years.