What is time?
I always used to think that the universe was a consequence of time. That is: say you would plot the universe in a graph, time would be the x-axis and the universe would be the y-axis. So the universe is affected by time, but the universe does not affect time. Is this correct or do for instance objects with great gravity (e.g. black holes) influence time?
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A resource I have too little of.
Also, I exert greatly on gravity and have yet to influence time in any meaningful way
a very complex question that i can’t really answer. but i may be able to give you food for thought on the topic.
time is essentially the fourth domension of the universe. you’ve probably heard of the space-time continuum. it’s a reference to the fact that space and time are somehow part of the same. one of my physics teachers tried to give insight to this fact by reminding us that you can’t get from point a to point b without taking some amount of time to do so. begs the question of a body at rest though as time stops for no one.
objects with mass affect the space around them – this is not conjecture but an observed fact. black holes are hugely massive and so massively distort the space around them to the extent that mass-less particles (photons = light) can not escape the space around them – not sure this is exactly correct, but the space around a black hole is somehow folded around the black hole such that there is no path through space allowing the photons to ecape. so in this case, it isnt gravity directly that affects the photons, but gravitity’s affect on space that directly affects the photons.
space and time being part of the same, black holes also affect time but i can’t even to start describe this affect – the subject of many god sci-fu movies and stories though!
here’s another very interesting thing to look into – entanglement. it refers to the so far as i know still theoretical effect knowing one fact about a particle can instantaneously have on another another particle somewhere else in the universe!
“Instantaneously” – this certainly defies my physics teacher’s thought experiment i mention above re: it takes time to get from a to b because in this case the effect is transmitted instantaneously and takes no time to take effect wherever else in the universe to impacted particle is located.
entanglement challenges notions about gravity, space and time mightily. i just started reading a book on the topic that so far i’d highly recommend, “The Age of Entanglement” written by Loiusa Gilder and published in 08 by Knopf. Check it out if you’re really interested.
and finally, the subject is really much deeper than i can treat it above. there are no shortage of books accessible to laypersons such as ourselves on the topic.
or not…entanglement poses serious challenges to Einstein’s special theory of relativity
This is a really subtle but important point: according to BIPM,
The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom
That is, we measure time relative to a regularly occurring phenomenon. Time is defined by what our clocks measure!
Beyond this, there is an important notion of an “arrow of time”. That topic is best reserved for another fluther question.
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