Part of my job is to answer questions from High School science teachers, and I love it! These last questions came from a teacher and her year 11/12 students. I thought the questions were good and showed the great depth that some students are thinking at, and also the great interest in science.
I hope I’ve given them justice. This stuff can get quite mind-warpy very quickly!
How do we know how many light-years away we are seeing - as in we have seen stars 13 million light-years away.
Redshift will tell us the velocity of galaxies away from us, then with a calculation as fundamental as c=fλ we can approximate it’s distance. BUT…It’s not a simple as that…of course! There are effects due to our atmosphere, relativity, gravitational lensing, objects in the way, expansion of space etc that get in the way of accurate measurements.
So, we have to KNOW the distance to a whole bunch of objects in order to compare that with others. There are a few ways to do this, either with cepheid variable stars, quasars, pulsars, and parallax. There are a couple of satellites that are tackling the problem with parallax that are very interesting.
Have a look at Hipparcos and Gaia. These two satellites are involved in Astrometry, a very interesting area in astronomy. Literally measuring the stars! The precision is amazing by the way. Gaia can detect a movement of a star of 10 microarcseconds, (or something like that) the equivalent of seeing the length that my hair grows in 10 minutes from a distance of 10 meters. The angle between the smallest division on a protractor is a degree, that’s made of 60 arc minutes, each one of those is 60 arc seconds, and then 10 1000ths of that!
With all of these methods, we can get some very accurate measurements.
The text book states that when the universe was one second old it was at least 1 light-year across but wouldn't that mean it was expanding faster than the speed of light?
YEP! It’s called inflation, and it is not very well understood! We talk about it as if we know what happened, but we really don’t! (like when we talk about how we know what the universe is made of, when we really only know what 4% of it is made of!) The experiment BICEP2 had a pretty close shave with the answer, but there is still some discussion, and of course we need to replicate the experiment.
Due to the fact that we don't understand inflation, we need to observe it and measure it, once that has happened, we can then start to try and figure out some details. So in order to measure it, we've tried to measure the effects of what that period would've done to the gravitational environment. In short, we're searching for gravity waves
If the universe started to collapse - could you travel fast enough to escape and can you exist outside the universe?
No. The idea of existence outside of a universe is, with our current understanding, non-sensical. If the universe collapsed, so would everything in it. The physical space between galaxies, stars, planets, etc would also collapse. Think of the usual stars (dots) on a balloon. If you deflate a balloon, the balloon also shrinks, the stars don’t move independent of the balloon, and interestingly (and in line with the analogy) the dots also get smaller!
The idea of “outside" the universe is not defined in physics (like dividing by 0, you just can’t do it. The idea of putting things into 0 groups is a non-sensical idea!) Space and time break down, we have no way of describing that condition mathematically or physically.