This is very confusing to me, so the question might be same. Please go through it, if required i will add more text.

According to Einstein's theory of general relativity, photons are not technically affected by large gravitational fields; instead space and time become distorted around massive objects and the light simply follows this distorted curvature of space.

My questions are: 1) For example: 1 hour near a black hole, is equivalent to 100 Years on Earth. If the light travels through this distorted space and time around a black hole, how much earth time does it take for light to cross the black hole's gravity?

2) We say the Universe is 14 Billion Years old, and its diameter is 91 Billion Light Years approximatly. My assumption is, these age and diameter of universe is based on the measurement of the light travel (Light is one of the factor in many).

3) So, if first (1) and second (2) points are right, how can we say the Universe is created 14 Billion Years ago (if light takes 100 Earth Years to cross over the black hole's gravity)?

  • $\begingroup$ Please take care of your spelling and punctuation in the future. Question marks, capitals, 'through' instead of 'thru', proper sentences. That will make it a lot more pleasant to read. I understand English may not be your first language, but punctuation is not a matter of what language you're used to. ;-) $\endgroup$
    – user1991
    Dec 10, 2015 at 11:05
  • $\begingroup$ No worries. Did my answer help you with your question? $\endgroup$
    – user1991
    Dec 11, 2015 at 14:55
  • $\begingroup$ Good one @user1991 I dont think this is a language related web site neither forum. Many great people has already answered the question, do you understood the question, if not ask me i will explain me. Please stop posting this kind of messages which doesn't questions $\endgroup$ Jul 24, 2019 at 4:00
  • $\begingroup$ See, I don't understand this comment. What are you trying to tell me? "which doesn't questions" doesn't mean much to me. Like I said in my comment (4 years ago...) is that punctuation is important in asking a question. Furthermore, it seems I was the one to answer your question - so I think I was in a fair position to complain. $\endgroup$
    – user1991
    Jul 24, 2019 at 8:08
  • $\begingroup$ perfect, we will use spell checker and grammer checker next time, as AI is also increasing in demand now a days. Cheers. $\endgroup$ Jul 25, 2019 at 3:03

1 Answer 1


You are quite right: Einstein's theory says the curvature of space is locally deformed. The essence of this is captured in the spacetime 'metric', a mathematical tool that tells us what space looks like and, derived from this, what is meant by 'a straight path', which photons take. If there is no source of gravitation present, the path of a photon will be what you know intuitively as a straight line. However, for some mass concentration (e.g. a black hole, as you say), this path will be bended such that the mass concentration acts as a lens. This is immediately clear from this image from the CFHTLenS survey:

enter image description here

Crucially to your question I think, you must remember that photons do not experience time and their speed is equal to $c$, the speed of light. Photons are not unaffected by their movement through a gravitational field, mind you: but this shows up as a gravitational redshift (for a time-varying potential), rather than a time delay (other than the slightly elongated path, perhaps).

Besides that, the age of the Universe is typically not quite measured as you say, but rather through parameter estimation in e.g. the cosmic microwave background. The effect of gravitational lensing needs to be taken into account for that, but not in the way you presume.

Also, remember that an extreme gravitational field such as that of a black hole is relatively rare, and even if it did delay the photon for a 1000 years that is still a tiny fraction of the age we would, according to your way of thinking, infer; the photon would have to encounter a LOT of such black holes for this 'effect' (which does not occur) to have a huge impact.

As a general point, you seem to have some (Interstellar-induced?) misconceptions about the universe, but I think that's not for me to address here.


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