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Time dilation and the big bang

  1. Jun 5, 2015 #1
    When we talk about the BB occurring 13.8Billion years ago (see time chart below)


    Does a 1ns of interval time at each of those points in time mean the same thing as a 1ns interval of time now, or is the measurement of time affected by time dilation / gravitational field effects as a result of the expansion of the Universe? For example events occurring at a black hole greatly slow down when we might look at them from earth.


    One tiny unrelated question, hope you don't mind: I wondered why we are still building these large ground based telescopes? I thought we were building the JWST to avoid atmospheric interference?
    Last edited: Jun 5, 2015
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  3. Jun 5, 2015 #2


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    1ns is 1ns, either then or now - it is the time taken by some physical process under the same conditions. Where time dilation comes into play is when we look at those past processes, and we seem them redshifted : a process taking 1ns at the CMB emission time is seen today as stretched out to about 1 microsecond, though this is usually translated into frequencies : a photon emitted then in radio frequency is seen now in the infrared.
  4. Jun 5, 2015 #3


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    Just a comment on your separate question, Tanelorn. That's a nice graphic in the article you pointed to:
    It shows the HST and the future James Webb space telescope in the lower lefthand corner, to give an idea of their scale compared with some ground-based telescopes. The article explains why large mirror size (much easier to achieve on the ground than in space) is important. There is a lot to study in the sky, different instruments are suited to different purposes. Ground-based telescopes get intensively used. It's exciting to see new even larger ones getting funded and constructed.
    Last edited: Jun 5, 2015
  5. Jun 5, 2015 #4


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    Pretty cool chart! One thing to mention @Tanelorn since you mentionned atmospheric interference, is that many (or most) large ground-based telescopes, in addition to being located in high altitude dry climates, use sophisticated active optics to correct for atmospheric distortion in real time - this does not cancel out all atmospheric effects, but it does make them competitive with space based instruments for many tasks.
  6. Jun 6, 2015 #5
    Thanks for replies guys.

    Yes Marcus, I was also very impressed by the graphic in that article and thought everyone here might like it.
    I am sure there is a reason why they need to put the JWST in orbit, something which ground based cannot do well, but I am just not sure what it is now.

    Back to the original question, does the time dilation effect where we might observe a 1ns event taking as long as say 1us, change the how long the initial events of the BB really take and how old we estimate the Universe to be? Or are the numbers in the time graphic already corrected to include this effect?

    In other words, when we put time numbers on events do always talk about how long they actually took, and not how long they were observed here on Earth to take?
    Last edited: Jun 6, 2015
  7. Jun 16, 2015 #6


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    Bear in mind the JWST is designed for infrared astronomy which is very difficult on earth.
    Last edited: Jun 16, 2015
  8. Jun 17, 2015 #7
    Recent developments in adaptive optics have made ground based telescopes more viable as they can cancel to some of the atmospheric noise.
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