# Is the flow of time regular?

Is the flow of time regular? How would we come to know if the our galaxy along with everything in it stops for a while(may be a century) w.r.t to the galaxies far beyond our reach. Is there a way to know if flow of time is smooth,or irregular?

PS I would describe myself as an illiterate physics enthusiast, so I hope you'll forgive me if my ignorance is borderline offensive.

• People are asking how you define "flow of time". Let me know if you agree with the following reformulation of your question: "Is it possible to observe a location in space-time, wait a couple minutes in your reference frame, then observe the same space-time location?" In other words, you look at the same spatial location a little later, and note that the time coordinate has not changed. I don't think this is possible. – mbeckish Mar 18 '14 at 15:15
• When I read this question I thought of the question of whether the universe is a simulation. If that were the case, whatever was running the simulation might not (for example) even run/update Andromeda's current state until just before its light cone hits us. – Michael Mar 18 '14 at 17:13
• Related: physics.stackexchange.com/q/15371/2451 , physics.stackexchange.com/q/41237/2451 , and links therein. – Qmechanic Mar 18 '14 at 20:35
• Tom, be aware that it isn't good form to edit your question into a significantly different question after a number of answers are given and have been upvoted. What I recommend you do is roll back your edit to the original form of the question, select an answer for it, and then create a new post for your revised version of the question with a link to this one for reference. – Alfred Centauri Mar 19 '14 at 16:34

Note: This answer addresses the question in its original form:

Is the flow of time regular? How would we come to know if the whole universe along with everything in it stops for a while(may be a century). Is there a way to know if flow of time is smooth,or irregular?

Flow with respect to what? Regular with respect to what?

How would we come to know if the whole universe along with everything in it stops for a while(may be a century)

A century as measured by what? If the "whole universe stops", what would "a while" mean? "a while" according to what? What would "stops for a century" mean?

If you think carefully about the premises of your question, you'll find that you're imagining a 'meta clock' that doesn't stop when you stipulate that everything 'stops' (stops according to what?) and by which one can judge the 'flow' of ordinary time. Closely examine that premise.

• This bugs me so often in sci-fi books, movies, and fans. – Paul Draper Mar 19 '14 at 5:47
• I have updated my question. – Tom Lynd Mar 19 '14 at 11:36
• For the updated question (time in our galaxy stops for a century w.r.t. some other galaxy), it is identical and indistinguishable to the case for our time flowing normally, but that other galaxy suddenly jumping 100 years ahead. It wouldn't happen immediately, since it takes time for information to come to us; but in that case, we could notice the jump as a sudden huge increase in observed light from that galaxy - as 100 years worth of their emmitted light arriving at once. (the details of "at once" being dependant on how that impossible time pause happened). – Peteris Mar 19 '14 at 11:42
• @ Peteis, As I mentioned in the updated part that those galaxies are well beyond our reach. what if the light from that galaxy reaches us after billions of years? Moreover, as you describes jumping of time,as far as I know, there's no jumping of time in Reference frames rather time becomes slower or faster w.r.t each other.(Again I hope you'll forgive me if my ignorance is offensive.) – Tom Lynd Mar 19 '14 at 14:29
• @TomLynd Exactly - if some phenomenon only happened w.r.t a galaxy a billion light years away (and not regarding any galaxies just 0.9 billion ly way), then we'd only could know after a billion light years afterwards. As for "jumping of time" being impossible - your question was, in essence, 'how would we know if it happened', even if "it" is currently thought to be impossible. – Peteris Mar 19 '14 at 20:25

Have a look at my answer to Is there a proof of existence of time?.

The problem with your question is that the concept of the flow of time is an elusive one. We measure flows with respect to time, for example velocity is $dx/dt$. So how can we measure the flow of time? If we simply say it's $dt/dt$ then obviously that is always one.

The only possible answer to your question is that no, we cannot know whether the flow of time is smooth or irregular. But this is a somewhat misleading answer since the flow of time isn't well defined.

• I suppose you could say that "time is not a dynamic variable". – Kerrek SB Nov 23 '14 at 21:18
• @KerrekSB On the contrary, time has been proven (thru clocks-in-jets experiments) to dilate at relativistic velocities, as well as in more intense gravitational fields than those present locally, and acceleration in the attainment of those velocities or locations itself requires time. Also, because every duration of time contains every briefer duration of it, its consideration as a concept separable from conceptions of the other components (spatial dimensions) of spacetime events is feasible, even though its physical separation from those components may not be. – Edouard Jul 22 at 18:26

The simple answer is that in our everyday world where velocities are much smaller than the velocity of light, yes time is as regular as space. If you rule a football field as 100meters by 100 it will stay that way whenever you measure it ( unless there is an earthquake of some such disruption). We have rulers defined in France for the meter, and we have clocks defining the time. Starting with pendulum clocks whose frequency does not change and it measures time to the Cesium clocks that measure time even more accurately, the flow of time is constant.

If one goes to special relativity and has two systems moving with relative velocity close to the velocity of light time slows down when each system looks at the other from a framework at rest, and space is seen as distorted in the direction of motion of the moving frame, but that is another story. Within each framework time flows uniformly.

In General Relativity where there is gravity it means that space and time are distorted so as to generate the gravitational fields we see, and that is still another story.

Absolutely no. The best known counter-examples are the clocks on board the GPS satellites. If the flow of time was "regular" , they'd run just as fast as any other clock. In reality, they run slower - precisely as predicted by relativity theory. So there's a clear discrepancy between us down here and a satellite that's just a few hundred kilometers up.

• If he means the flow of proper time, this answer is invalid. – jinawee Mar 18 '14 at 17:44

Under Special Relativity the flow of time should be inferred to be regular for a single observer because the speed of light is invariant with regards to the single observer. Observers in the same reference frame will measure the same value for the speed of light, and as a consequence experience the same flow of time.

Your perception of time may vary as noted in the (perhaps apochryphal) Einstein quote referenced elsewhere, but at a physical level, your physical experience of time is regular.

As BICEP2 has shown, spacetime has been significantly irregular, enough to change how electromagnetism propagates. Especially considering relativity, time is not regular. Deviations from a "uniform rate of time" are not easily observed, but different rates are now measured daily worldwide: GPS must account for a small (per second) rate difference between satellites and Earth's surface, which would introduce large (per kilometer) errors in location.

Is the flow of time regular?

Picture a leaf floating downstream on a river in the pitch dark. As the river gets narrow it speeds up, and as it gets wider it slows down. The leaf has no light to see the shoreline so from it's perspective there is no change in the flow of the river.

Now what if the light turned on?

The leaf could now see the shoreline, but from a physics point of view. This shoreline is the background radiation of the universe. It's so far away that as we move down the river we can't perceive any movement in the shoreline. Therefore, we can't tell if the river speeds up or down.

The only way would could tell is to look at the shape of the shoreline. Are there points on the shoreline moving closer and/or further apart. How could we tell the difference between changes in time or changes in the shape of the shoreline?

That is why people study the big bang. To predict what the shape of the shoreline should be, and then see if there are any unexplained changes.

How would we come to know if the whole universe along with everything in it stops for a while(may be a century)

Time for a human is perceived not in the current moment, but in the memory of previous moments. Humans remember time passing as our brains record past events. If time stopped for one individual, then it would be like pressing pause on a VHS recorder, but when time stops for the universe then everything stops. Even the VHS recorder would not record a gap in the video since the inputs to the VHS paused as well.

The universe could stop and continue. We'd have no perception of the events. Since it's a completely untested event. It means it never happened. Even if it did.

Our perception of time is irregular. "A watched pot never boils" and the effect of being able to perceive minute details when in a crisis - pebbles shot from a wheel and the colour of a band around the tyre as you are about to be run over for example.

Energy, Space and Time all are granular. The difference betwenn them are the unbelievably small dimensions of the smallest space and time steps, as opposed to the rather largish smallest energy quantum h. Which is large enough to have been proven experimentally 100 years ago. (Which is what earned Einstein his Nobel prize.)

The granularity of time and space will will be out of reach for experimental physics for pretty much all times.

So, there is no flow of time, the universe ticks. But if these ticks are and have always been the same ist not known.

• If you're going to answer with something like this, please state your sources. In this case though, you claim time and space are quantized but then say it's out of reach of experiment. Please leave untested claims out of your answers. -1 – Brandon Enright Mar 18 '14 at 16:58
• @Brandon - check 'Planck time' and 'Planck length.' Whether or not space-time is physically quantized, there are practical values which render time and space as granular whether we like it or not. – user1329482 Mar 18 '14 at 17:14
• Check the meaning of Planck scales, they just mean that there must be something beyound our theory, not discreteness of space-time. – jinawee Mar 18 '14 at 17:45

## protected by Qmechanic♦Mar 18 '14 at 17:24

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