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Age of The Universe - Time vs Space

  1. Feb 22, 2006 #1
    I have long wondered about this. When light takes x number of billion years to reach earth, we judge that the star emitting the light is x number of billions years old. I cannot understand that the star would be the same age as the distance it is away from us. If I was riding a spaceship at the head of that beam of light, I would not age the same as people, i.e.time, on earth. I would, in fact, be much yonger in years than the distance in light years traveled. Is this right? If it is, then would we not have to recalulate the age of the universe using this type of equation?
  2. jcsd
  3. Feb 22, 2006 #2


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    Well your first assumption is wrong. We get light from the sun in 5 minutes but that doesn't mean the sun is 5 minutes old...
  4. Feb 22, 2006 #3


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    It's 8 minutes, Pengwuino, but you're right, there's a misunderstanding here.

    Properly phrased, the concept is this: If you're looking at an object that is a billion light-years away, you're seeing light that was emitted a billion years ago. You are, therefore, seeing the object as it was a billion years ago.

    The age of the object -- the time since it formed -- has nothing to do with it.

    - Warren
  5. Feb 23, 2006 #4


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    Hi Buttonpusher! Welcome to PF. Plenty of brain bending concepts are regularly tossed around here. Chroot gave a very nice answer. Hopefully, I can expand on it a bit. If you were a photon, travelling at the speed of light, your wristwatch would indicate you had traversed the distance between your home star and earth in no time flat. You would look exactly like you did the moment you began your journey, aside from some bending and stretching effects.
  6. Mar 3, 2006 #5
    I thank you people for enlightening me on this subject. I understand now that when traveling at the speed at light, I get there quicker in time while the distance traveled remains the same.
    Do not worry about your difficulties in Mathematics. I can assure you mine are still greater. - Albert Einstein
  7. Mar 3, 2006 #6
    Actually, I believe that if you're going to use the "zero time" picture of light you must also have "zero distance". Physically this should be reasonable since if no time passed you didn't go anywhere.

    Speaking more geometrically, as a velocity approaches c relative to some inertial observer both the time and space axes rotate up towards the 45 degree line on a Minkowski diagram, in the limit as v approaches c all of the events in space-time approach one single event.
  8. Mar 3, 2006 #7


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    What on Earth does this have to do with the OP's question??? (Sorry to pick on you Dicey, you're one among many). These answers are worse than no answer at all, as they actually confuse the matter.
  9. Mar 3, 2006 #8
    The OP's original question had already been answered, I was responding to his comment that "when traveling at the speed at light, I get there quicker in time while the distance traveled remains the same".
  10. Mar 4, 2006 #9


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    Under GR, traveling at the speed of light completely negates any consideration of distance. A photon, unless intercepted, traverses the entire universe in no time whatsover [by her watch]. Study the Einstein equations and this will become apparent.
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