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magpies
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The real test for if something is real or not is if it can be destroyed right? So why don't we start work on a time bomb that destroys time it's self that way we can at once have the answer to these questions :)
petm1 said:I see time as a dilating area from every massive point within our visible universe, think light waves. We see time by putting the billions of photons from all the different light waves together as our individual presents. We may be able to map our world lines through space but it is our center connection that we map through time.
the web of connections between things along their light-cones
We still tend to imagine the universe as if it were Newtonian
But obviously no one experiences the world that way -- as if you could stand outside of space and time and see the whole thing at once. It seems that learning to imagine the world as we actually experience it, in real time, is a unique challenge.
apeiron said:About 2.725 degrees K according to the CMB clock .
It's interesting that after stumbling upon this thread Scientific American releases this article called Is Time An Illusion? Thought it might be worth sharing here.
petm1 said:Describing time as physical must count for thinking of time as real, I would think.
ConradDJ said:That's definitely one of the things it is.
"Up and down are different, because of gravity."
How does one establish up (or down) as a separate spherical radial from a gravity locus? Is gravity smooth or discrete in terms of directions from a locus? Does the size of a gravity locus ( planet vs ball bearing ) determine or change the spherical radial gravity direction arrays? It seems impossible for an object to have an infinite number of gravity vectors, so up and down are pretty useless generally as terms.
Descartz2000 said:"Is time real?" :
I think asking what 'real' means is confusing. I think it comes down to the following question: if there are no inherent value differences between 'present/now' states, then how can I claim any single 'now' state is more in existence than any other? If 'real' equates to 'existence', then yes, I would argue time is real.
Mu naught said:This is a troubling question for me. Certainly there exists in our universe sequences of events which may or may not be undone easily. For example, I can walk 31 steps forward, then walk 31 steps backward and return to where I was. However, I can not easily unmix milk from my coffee after I have poured it in, though I shouldn't think it is impossible.
This isn't really what we mean when we think of the concept of "time". A simple sequence of events is something we can do or undo, but no one here thinks they can return to yesterday, or last year. When we think of time, we think of us somehow floating along in a bubble that we call the present, and behind us is the past and before us the future. We can not look forward into the future, but we can look behind us into the past and around us inside the bubble at the present. I personally suspect that this is really an illusion, and that the concepts of "past' and "future" have no physical meaning, but trying to prove it in any concrete way I think is beyond my scope for now. Any thoughts on this topic?
Ivan Seeking said:If the past were not real, would the equations from GR tell us that?
Pythagorean said:It depends on what you mean. It's not as if the whole universe stepped through increments of time together, in sync. So what do you mean by past? The local past of a stationary chunk of space? GR tells us that time is not absolute, so the idea of "past", as we intuitively view it, is misleading.
Of course, I wouldn't say it doesn't exist; just that it doesn't exist as we know it.
Ivan Seeking said:The laws of physics are assumed to apply everywhere.
In the case of a time machine, we are talking about the past wrt the frame of reference of the observer.
Pythagorean said:It depends on what you mean. It's not as if the whole universe stepped through increments of time together, in sync. So what do you mean by past? The local past of a stationary chunk of space? GR tells us that time is not absolute, so the idea of "past", as we intuitively view it, is misleading.
ConradDJ said:I agree it's important to point out that past and future have meaning from some particular standpoint in the world -- not globally.
Pythagorean said:What do you mean by that? It shouldn't contradict what I'm saying.
GR tells us how matter shapes space and time, SR tells us how motion does. One could argue that such tools would be useful in constructing a model of an observer's past, but naturally, even predictive models don't have the final say on whether something is real or not.
It would be strange indeed, if an observer was able to reduce the entropy of the universe in his frame, while time-traveling (bound to be an entropy-increasing event). I can hardly perceive of how you'd ever travel backwards through time in the first place, or how you'd get the rest of the universe to cooperate with you.
a) either all "pasts" would have to be recorded somewhere physical (if that's even possible) so that you had something to "travel" to.
or
b) you'd have to somehow move all the particles back into the position of a past (but because simultaneity doesn't exist, I'm not sure how you'd ever manage to do that.)
To me, time travel on the same footing as intelligent design: that is, if you want to nitpick, it could be true, but it's highly unlikely.
Ivan Seeking said:Nonetheless, we get real solutions using various schemes, and GR, suggesting that time travel to the past is theoretically possible. Therefore, it would seem that GR predicts that the past is real. Yes, no?
To me, your argument sounds a bit like saying that clocks in SR don't really run slowly as a function of speed, wrt a fixed observer, they just appear to run more slowly.
apeiron said:No, I would still suggest that the idea of locally symmetric time is an assumption, a helpful simplification, of Newtonian mechanics, carried over into relativistic mechanics. Backwards and forwards in time have no differentiation only in those kinds of theories.
But a thermodynamic model of reality does give you a basis for a "more realistic" view of time as an asymmetry. I don't mean thermodynamics as in Boltzmann's statistical mechanics - which, mechanically, locally, again defines no arrows - but thermodynamics as in the modelling of the dissipation of entropy gradients.
loseyourname said:Well, at least on this planet, we have a far simpler indicator of time direction: living creatures and born and then later die. It never happens in the reverse direction. Trees don't shrink into saplings and then seeds.
But isn't thermodynamics a bit problematic, conceptually? Why not just work on modelling the universe in terms of a global wave mechanical view of things based on some fundamental dynamical laws governing it's overall evolution? Is this simply out of the question because it would be, eventually, too complicated?apeiron said:But a thermodynamic model of reality does give you a basis for a "more realistic" view of time as an asymmetry. I don't mean thermodynamics as in Boltzmann's statistical mechanics - which, mechanically, locally, again defines no arrows - but thermodynamics as in the modelling of the dissipation of entropy gradients.