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Speed of universe and quantum theory

  1. Sep 15, 2006 #1
    I have just read slate.com which debunks string theory. What I am about to say will probably display my ignorance and lack of education however I am trying to understand QT. Here goes.

    I have read the universe is expanding. I, in my elementary way, understand QT is a condition where you may measure where an electron is fired, or you may determine where it impacts, but you cannot do both. I know this is just a small part of the 3rd law of TD, however if what I say is true, has anyone ever taken into account the speed of earth through space or put another way has anyone ever taken into account the expansion rate of the universe?

    I would think if an electron travels at the speed of light, it may appear to an observer, to be actually traveling faster than light. Therefore if we know the expansion rate we could take that into account and determine not only where the electron came from but where it impacted. I have had this question for many years and thought I would ask. If I am negatively impacting your forum, no one will answer and I will politely go away. Sincerely, I am truly interested. Thanks.
     
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  3. Sep 15, 2006 #2

    selfAdjoint

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    It's really good that you're willing to learn. We here will be happy to explain. I have to say that there are a lot of problems with you understanding right now, but you sort of expected tha, right?


    That's not quite right. I think what you're aiming at is the uncertainty principle: You can measure the momentum of something perfectly, OR the position of that same thing perfectly, but not both; the uncertaintly of your measurements of the two quantities are inversely related so that when one goes down, the other goes up. But this concerns measurements taken at the same moment, not at an emission time and an impact time.

    The amount of uncertainty in the position or speed of the Earth is inversely proportional to its mass, so it's a tiny, tiny number. It doesn't affect large scale physics at all. This is still more true of the universe! You do know that the universe that's expandin t=is the whole bug spacetime with stars and galaxies and all, not just the Earth itself, right.

    First, an electron has mass (510 electron volts) so it CAN'T travel at the speed of light. Then I don't see where you're coming from on how it would appear.

    Once again, I don't see how your reasoning works on this.

    Sincere interest is the magic passkey. Say on!
     
  4. Sep 15, 2006 #3
    Yes I did expect feedback on my lack of understanding but thanks for doing so. I read the "Elegant Universe" but I didn't study it. The book turned on some lights for me and in other areas I was lost. I will continue trying to learn, what I call a most difficult area. Thanks again.
     
  5. Sep 15, 2006 #4

    selfAdjoint

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    May I recommend a book? It's Feynman's QED, The strange story of light and matter. Feynman's approach is a lot less confusing than most introductions to quantum mechanics.
     
  6. Sep 18, 2006 #5
    Is this true for something like a tennis ball?
     
  7. Sep 19, 2006 #6

    selfAdjoint

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    Yes but the uncertainty is too small to measure.
     
  8. Sep 19, 2006 #7
    I'm imagining a tennis ball shot along a known path where there are detectors along the path. When the first detector is set off the time is recorded and right after that there is another detector that records the position and time. I would think that at this moment we would be recording the momentum and position correctly, but I know this is wrong. Is it because the path is known? or is it something else? Where does the tiny uncertainty arise from? Thanks.
     
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