Question on Time and Telescopes.

[Di Wonderin]

This no doubt rates as a newby's first (and probably not last) stupid question, but the answer is out there, so break it to me gently, pleeeaase.

Having learned more of Astronomy from Assimov and ilk than from anything approaching education, and being borderline numerically dyslectic, I have only a 'visual' form of knowledge and interest in the field. Pure amateur. I've now retired and have more time to think about all that I don't know about it yet. This question has vexed me for some time and I just know there's a simple answer, but I can't find it.

I understand that when we look at a distant object we see it as it was, not as it is now, due to the speed of light.
I get that looking at distant objects is tantamount to looking into the past.
What bothers me is the newer discoveries, and statements, that we can 'see' the 'Big Bang' formation of the Universe.

Given that, to my understanding, light speed is the upper limit of anything getting anywhere, and that presumably the Universe couldn't expand faster than that, how did we get here before the light from the Big Bang?? Wouldn't that initial light emission be well past this point by now???

Is the whole reported discovery being warped by journalese and what we are really seeing is just the residual 'glow'? Or am I hopelessly clueless, and will I, as my username suggests, die wondering?

[Chris Peterson]

I understand that when we look at a distant object we see it as it was, not as it is now, due to the speed of light.
I get that looking at distant objects is tantamount to looking into the past.
What bothers me is the newer discoveries, and statements, that we can 'see' the 'Big Bang' formation of the Universe.

Given that, to my understanding, light speed is the upper limit of anything getting anywhere, and that presumably the Universe couldn't expand faster than that, how did we get here before the light from the Big Bang?? Wouldn't that initial light emission be well past this point by now???

The speed of light does not limit how fast different parts of the Universe can move with respect to each other. Most of the Universe is, in fact, moving away from us at much faster than c. The "oldest" photons we see are those that comprise the 3 K microwave background. Those photons were emitted by hot gas just a few hundred thousand years after the Big Bang. The regions of space where those photons were produced are now moving away from us at faster than c, and are therefore outside the observable Universe.

(Here is what relativity tells us about the speed of light: you cannot convey any information faster than c, and you cannot accelerate a massive body from rest to c; neither of these conditions is violated by different parts of the Universe moving apart at greater than c.)

[Di Wonderin]

OK, thanks for that aspect which never occurred to me, that the combined separation speeds are greater than c.

So what we 'see' isn't really the actual formation of the Universe as such, but the residual effects of it??

[Chris Peterson]

OK, thanks for that aspect which never occurred to me, that the combined separation speeds are greater than c.

So what we 'see' isn't really the actual formation of the Universe as such, but the residual effects of it??

Unfortunately, we can't see photons older than the microwave background because before the time those photons were produced, the Universe was opaque to electromagnetic radiation. The structure of the microwave background tells us a great deal about what happened earlier, but yes, it basically is what you are calling a residual effect.

In principle, we could see earlier using gravitational waves, which propagated through the Universe from the very beginning. We are only now learning how to make gravitational wave detectors. There is good reason to believe that within a few decades we might use them to peer beyond the microwave background, perhaps to the Big Bang itself.

[Di Wonderin]

I'll have to eat better and try to stick around long enough for that then.

Thanks for your interest, and answer. I'll carry on looking through old posts and advancing my education. It's nice to have the time to do it. Great site.