How can we see the big bang?
If everything started in the Big Bang, how can we still see it?' I think he's referring here to, for instance, what we dubbed the afterglow of the Big Bang or the cosmic microwave background radiation. He says, 'wouldn't the light from that event be well past us now unless we traveled faster than the speed of light in some way? So how can we still see it?'
Rosemary - Yeah. To think of this question, you have this big explosion and going away from the explosion, you have a lot of light, you have a lot of energy that's turning into mass, right? E = mc2. You can turn that energy into a mass. We actually did go faster than the speed of light but it's a tricky question. There's a lot of caveats to that. Imagine you have a stretchy sheet. Objects on the sheet, which represents space time - let's say marbles, are constrained to move below or at the speed of light, 300,000 kilometers per second. But the sheet itself can stretch faster than the speed of light. It's not constrained to this 300,000 kilometers per second. So although particles and things within this sheet have a speed limit, the sheet doesn't. So you can kind of get around this, it's kind of like you can walk on a train, right? You have your speed on a train. Maybe you're walking four kilometers per hour or something. But the train itself could be moving 90 kilometers per hour. And so because of that, we're still getting light from the Big Bang because we've kind of outrun it and now it's catching up to us. So now we're able to see this light, this energy temperature, the cosmic microwave background from all around us coming from the Big Bang, which is super, super cool.
Chris - In summary, then you are saying the universe is born, there's all these particles together sharing the same energy at that moment in time, which is what's going to ultimately give them the cosmic microwave background radiation as it is today. That bit of the universe, the sheet they're all sitting in, gets much bigger very, very promptly and much bigger than the speed of light. And drags the particles with it effectively. They haven't moved, but because the space between them has got much bigger, much more quickly. When we appear, we are seeing those things all over the place. In the observable universe. So we are seeing as though that light is coming to us for the first time.
Rosemary - Yeah and I think the really interesting thing about this is if you could see through this kind of fog, we call it recombination, around us, you would be able to see the big bang happening all around you if you had a super powerful telescope. Because when you're looking through space, you're looking back in time. And so in theory, if you looked in any one direction far enough, you'd see the Big Bang. And if you turned around and looked really far in that direction and you'd see the Big Bang. So the Big Bang would be happening all around you. Which is so incredibly weird.
Chris - Yeah, it is a bit mind boggling, isn't it? But the way you've put it very, very clear. Thank you for that.