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Time dilations: How do we actually see things?

  1. Nov 8, 2011 #1
    The subject of time dilations has always fascinated me. Sometimes the thought experiments can get confusing but there is one that always baffles me even though it should be simple.

    According to the theory time is slower the closer we are too dense matter. In other words time is slower on earth than it is 100,000 miles out in space and time speeds up the farther you are away from density.

    This is the part that gets confusing. I have also read that from our perspective on earth if we viewed activity far out in space we would see things happening slightly faster?? If we viewed other activity even farther out, would we see that activity at an even faster time frame??

    So if there is any truth in the above statements I have a question:

    If we observed a photon approaching earth at what distance do we first see it?

    Can we see it far out in space where time is faster or not until it hits our eyes or a combination?

    If we can see it as it comes in what will it look like as it comes in through the slowing time dilations?

    Would it appear to slow down the closer it came to density?

    If you in space between galaxies away from density would everything appear blue shifted?
  2. jcsd
  3. Nov 9, 2011 #2


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    There is nothing "Beyond the Standard Model" about these questions. Please ask them in the Relativity forum.
  4. Nov 9, 2011 #3
    wouldn't you see it when it hits your eye?
  5. Nov 9, 2011 #4
    The thing about 'photons', or any radiation, is that they have a 'source' and a 'sink'. That 'sink' is your eye when you look around. The 'photon' is only 'there' when you measure it. It's not like a ball coming at you in space. When it hits you it has a energy and a momentum, as a wave it has a frequency and wavelength that in a way can be seen as equivalent to energy and momentum. As the frequency decreases, so does the energy. The wavelength of an electromagnetic wave is inversely proportional to its frequency. So waves with high frequency have short wavelengths, and waves with low frequency have long wavelengths. How that can produce the colours and images we see I'm not sure of actually, maybe someone here knows?

    Time on the other hand is a definition of durations, as I think of it. Any 'clock' will do for measuring time, and the clocks durations can be evenly split down to Plank time. In relativity all clocks are influenced by motion and gravity, but, always relative the observer. To see that one you have to ask yourself if you ever notice your clock speeding up, or slowing down, ignoring bad batteries for this one. If you agree on that times arrow always seem to have the same 'flow' for you then you need to ask yourself why others 'clocks', according to you observing them, can slow down, or up, relative your clock. To see if it is a measure of 'time' being different there you can always go to that spot, planet, spaceship whatever, and then check if your clock gives you a new 'time rate' relative your heartbeats. It won't.

    A time dilation is defined from lights speed in a vacuum. That speed will always be the same locally, just as your 'time rate' heartbeats/clock. It doesn't matter how 'fast or slow' you move, it doesn't matter if you measure it on Earth or at a neutron star. You will never find 'c' to vary locally. Because if you could define the constant 'c' as a variable then relativity also would have to be reconsidered. And that is a experimental fact, that the theory of relativity was built on.

    So 'c' is weird, and 'c' creates a time dilation between 'frames of reference' together with gravity that, with a planet, can be expressed as a 'gravitational acceleration' (equivalence principle). But when you look at something your eye get filled by those 'photons', and they all come at you at the same speed, no matter from where they come, and how the 'clocks' ticked there, slower or faster than yours.

    There is one thing more to add, red and blue shift. That's also a relation between the observer and the 'light' he observes. But the 'energy' perceived by your eye will be real for you, or any detector. Earth is 'gravitationally accelerating', and so all in-falling photons will blue shift relative you. But if the source is going away, as you see it, then there will be an additional red shift of the light from that 'source', and if another is coming towards you then there will be an added 'blue shift'. As a photon won't change speed, it instead blue and red shift.
    Last edited: Nov 9, 2011
  6. Nov 10, 2011 #5
    Let me help you explain why time is slower nearer masses.

    Think about a rocket ship accelerating forward at a constant rate. Everything in the ship is always moving at the same velocity as the ship and everything else in the ship. At the front of the ship is a clock, at the middle of the ship is a clock, and in the very back is you, looking at both clocks. The back clock releases a photon every 100 seconds (from its point of view) and so does the middle clock. However, while the light is traveling from the front of the ship to the back of the ship, the ship is speeding up to catch the light before it would hit normally. Not only that, but the lengths in the ships and the time rate of the ship decrease. These affects are more prominent for the clock in the from of the ship that the clock in the middle. From your point of view, it looks as though the clock in the very front of the ship is releasing photons slower (more time between each photon) than the one in the middle.

    The Principle of Equivalence states that you can't tell whether or not you're in a gravitational field or accelerating absent of gravity. If you are in a speeding rocket ship in the middle of space, accelerating at 9.8 m/s^2, the feeling is the same as being in earth's gravity. So, if this time dilation occurs over a distance in an accelerating reference frame, then is MUST also occur in a gravitational field.
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