How do we know time exists?

Originally posted by johnnylongwoody
How do we know time exists?


Because there is always some ***&^<>""@@@
telling you that you're late.

Impermanence, my feer; wi' a wee Aberlour (a'bunadh) dram this too will eventually pass😵

Originally posted by black beetle
Methinks time is non-existent because the flow of time is impossible; if we accept that time is split into past, present and future, the conception of time loses its coherence because if the past is considered to produce the present and the future, the latter two parts would be already included in the past and it could not be properly said to have inher ence from matter; therefore, time cannot be conceived as if it were separated from matter
😵

I don't get it. You start by saying time doesn't exist, then finish by talking about time dilation and the way the rate that time passes is dependent on one's frame of reference. You seem to be contradicting yourself, unless by saying "time doesn't exist" you mean there is no absolute frame of reference that can be employed to judge the "true" rate that time elapses.

The theory of relativity certainly makes clear that four dimensions are required to locate an event. The fourth dimension is not a spatial one, however. It is time.

EDIT: It is true that someone traveling a fair fraction of the speed of light in a faraway galaxy may exist in a time frame that is contemporary, with, say, the year 2100 A.D. or the days of the Roman Empire (depending on the direction of travel). That does not render time nonexistent, nor does it make the ideas of past, present, and future meaningless. The equations are crystal clear, and all that we can say is that what constitutes the "present" at some particular location in space (or on some planet, say) will depend on an observer's velocity with respect to that location (or planet). But, in order to make the time on Earth when Napoleon was alive your "present", you have to be not only traveling very fast with respect to the Earth (either toward it or away from it -- I forget which), but you have to be millions of lightyears away from Earth as well. You can then say you live in the time of Napoleon, but you will have no chance to talk to him or interact with the environment that he inhabits because quadrillions of kilometers of space, and not time, now separates you from him. And so the idea of the past as a separate physical realm remains something with real meaning: you cannot personally access it, according to relativity theory. You're apart from it. Past, present, and future do mean something in the four-dimensional spacetime continuum.

Originally posted by Soothfast
I don't get it. You start by saying time doesn't exist, then finish by talking about time dilation and the way the rate that time passes is dependent on one's frame of reference. You seem to be contradicting yourself, unless by saying "time doesn't exist" you mean there is no absolute frame of reference that can be employed to judge the "true" rate that ...[text shortened]... present, and future do mean something in the four-dimensional spacetime continuum.

Hi Soothfast!

No contradiction; I see time as an (empty) property we attribute to all phenomena for our convenience, and I evaluate all these phenomena as phenomena-in-flux.

Also I do not separate time from the phenomenon known as matter; and I conceive a unique spacetime herenow (that came into being out of a cause-effect nexus that is depicted thanks to our knowledge alone, thus depending strictly on the knowledge we currently have herenow about it, due to the fact that the past is indefinite and shifting as for example the experiments of the delayed-choice quantum eraser show. That being said, I am of course aware of the fact that for our convenience we assume that specific parts of the past are static and well defined because we accept by definition that they are made only of known to us events that have already happened, as is the case at the Minkowskian spacetime etc) instead of various combinations of inherently existent self contained spatial and temporal dimensions
😵

Originally posted by black beetle
Hi Soothfast!

No contradiction; I see time as an (empty) property we attribute to all phenomena for our convenience, and I evaluate all these phenomena as phenomena-in-flux.

Also I do not separate time from the phenomenon known as matter; and I conceive a unique spacetime herenow (that came into being out of a cause-effect nexus that is depicted t ...[text shortened]... f various combinations of inherently existent self contained spatial and temporal dimensions
😵

That doesn't leave out the possibility that some future action can effect the past though.

I do see physicists trying to eliminate time in all their work, by substituting the flow of time with just relational events tied together like the position of a bouncing ball being not from one instant to the next but from one location to the next based on geometric considerations without reference to time.

"Eddington

In the 1928 book The Nature of the Physical World, which helped to popularize the concept, Eddington stated:


Let us draw an arrow arbitrarily. If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointing towards the future; if the random element decreases the arrow points towards the past. That is the only distinction known to physics. This follows at once if our fundamental contention is admitted that the introduction of randomness is the only thing which cannot be undone. I shall use the phrase ‘time’s arrow’ to express this one-way property of time which has no analogue in space.

Eddington then gives three points to note about this arrow:
1.It is vividly recognized by consciousness.
2.It is equally insisted on by our reasoning faculty, which tells us that a reversal of the arrow would render the external world nonsensical.
3.It makes no appearance in physical science except in the study of organization of a number of individuals.

According to Eddington the arrow indicates the direction of progressive increase of the random element. Following a lengthy argument upon the nature of thermodynamics he concludes that, so far as physics is concerned, time's arrow is a property of entropy alone.

Overview

The symmetry of time (T-symmetry) can be understood by a simple analogy: if time were perfectly symmetrical a video of real events would seem realistic whether played forwards or backwards. An obvious objection to this notion is gravity: things fall down, not up. Yet a ball that is tossed up, slows to a stop and falls into the hand is a case where recordings would look equally realistic forwards and backwards. The system is T-symmetrical but while going "forward" kinetic energy is dissipated and entropy is increased. Entropy may be one of the few processes that is not time-reversible. According to the statistical notion of increasing entropy the "arrow" of time is identified with a decrease of free energy.

If we record somebody dropping a ball that falls for a meter and stops, in reverse we will notice an unrealistic discrepancy: a ball falling upward! But when the ball lands its kinetic energy is dispersed into sound, shock-waves and heat. In reverse those sound waves, ground vibrations and heat will rush back into the ball, imparting enough energy to propel it upward one meter into the person's hand. The only unrealism lies in the statistical unlikelihood that such forces could coincide to propel a ball upward into a waiting hand."

-----------

Also refer to entropy, and entropy and the arrow of time.

References

"Arrow of Time", Wikipedia, the free encyclopedia, http://en.wikipedia.org/wiki/Arrow_of_time - quoted 16/1/2556 19.57pm

-m. 😉

Originally posted by sonhouse
That doesn't leave out the possibility that some future action can effect the past though.

I do see physicists trying to eliminate time in all their work, by substituting the flow of time with just relational events tied together like the position of a bouncing ball being not from one instant to the next but from one location to the next based on geometric considerations without reference to time.

Hi sonhouse, it's been some time; best to you and yours!

Edit:"That doesn't leave out the possibility that some future action can effect the past though."

In case we destroy the information (about the past) we just received herenow, we would simply have the information eliminated;


As regards the elimination of time, methinks it cannot be eliminated in relativity, for what one observer views as space, another views as time and vice versa, because spacetime is unified, like the two sides of a single coin.
However I join hands with Smolin and I see a coordinate system out of spacetime (time on one axis, and on the other one 3D space) and momentum space (energy on one axis, and on the other 3D momentum). And when I imagine the momentum space curved in a non-metric way I have the impression that spacetime is relative; and therefore I have an interesting vision of the observer universe: a coordinate system of relative spacetime on one axis and relative momentum space on the other
😵

Originally posted by mikelom
"Eddington

In the 1928 book The Nature of the Physical World, which helped to popularize the concept, Eddington stated:


Let us draw an arrow arbitrarily. If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointing towards the future; if the random element decreases the arrow points tow ...[text shortened]... pedia, http://en.wikipedia.org/wiki/Arrow_of_time - quoted 16/1/2556 19.57pm

-m. 😉

Yes😵