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Three questions about physics

  1. Apr 12, 2012 #1

    Below are three questions. I realise that they’re probably better described as three different ways to announce that I’m stupid, but I’m hoping there are answers. I have tried looking these things up, but I haven't really got anywhere, and am as confused as ever.

    I apologise for the length and incoherence of the questions, but I thought it might help if I tried to fully describe what’s bothering me.

    Many thanks in advance to anyone who takes the trouble to answer.

    1. If I set fire to a stick, I create light. Where precisely does that light come from? I think I mean from what particle (or part of a particle) does the light begin? The application of heat to the stick causes something to happen to x, as a result of which x produces a photon, so what is x? And what was the photon before it become a photon (i.e. before the heat was applied)? Basically (I think), where do photons come from or how are photons made?

    2. The universe is expanding. At what velocity is it expanding? Can there be said to be an outer edge of space-time (like the shockwave of an explosion)? What exactly is it that is expanding – is there actual stuff which is going somewhere new, and if so, what is that stuff? And if there’s a finite amount of stuff in the universe, is the stuff that’s going somewhere new leaving gaps behind it, or are things becoming increasingly thinly spread?

    3. Am I made of space-time, or do I exist within it? I mean, is everything that is me (or you, or a pencil, or a star) a separate entity, or a particular configuration of space-time, rather like a condensation of stuff in a bigger pool of the same stuff (stuff being, I suppose, space-time)? I think this question might simply be this: are objects (or matter) merely collections/points of density in a big pool of space-time?
  2. jcsd
  3. Apr 12, 2012 #2
    1. Well, first of all, the energy was originally stored in the chemical bonds of the stick. As for where it comes from, if I'm remembering correctly, the heat basically causes some of the bonds to break, releasing the energy in them, and it's released in the form of light (and heat, which, in this case, is just infrared light.)

    2. The Universe is expanding, but ... well, I'll use the standard analogy. Take a balloon. Mark a few point on it to be galaxies. Blow it up. Note that on the surface of the balloon, each galaxy is moving away from every other galaxy. Also note that closer galaxies don't move away as quickly as farther galaxies. Also note that no galaxy is the centre of the expansion. This is a decent analogy to the expansion of our Universe. Also note that, while gravity and expansion complicate things a bit, what we can see is what has produced light which has had time to reach us. One would expect about a 13.6 billion light year radius to the observable Universe, but, due to gravity and expansion, the grand total is actually 45.7 billion light years in radius. Also note that the further we look out, the earlier in the Universe's lifetime we are seeing.

    3. I don't know if this is known for sure, but I'm pretty sure matter's, well, a bunch of particles interacting within spacetime, which they actually distort a bit through gravity. Whether those particles are point particles, the current theory says that they are, but one of the theories that, um, patches it up, known as String Theory, postulates that they have some size. ST's still a work in progress, and despite how long it's been thought of, it's still just starting.
  4. Apr 12, 2012 #3


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    Gold Member

    Three very good questions.
    Three very good answers.
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