Tell me more ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.
up vote 32 down vote favorite
10

I was making universe simulations, and I noticed that I implemented discrete time (the only type possible on computers). By that, I mean that I had an update function, that was called many times per second, but it advanced the world for one simulated second each time it was called. I was a bit intrigued by the concept. Is the real world "updating" continuously, or in really small, but discrete time intervals?

share|improve this question
Why don't you use a timer (for each item in your array) that is set to fire at the desired time? instead of firing the timer every 60 seconds. Assuming the app would be running all the time. – user11951 Sep 5 '12 at 12:36
Hey, I appreciate the comment and all, but this doesn't really answer my question. I asked about the real, physical world, and provided my simulations only as a source of that curiosity. – Yannbane Sep 5 '12 at 13:09
Also, I'm not sure what do you mean. I do have timers, but I advance the world in discrete time intervals. – Yannbane Sep 5 '12 at 13:09
3  
I would also add that using n timers to run a simulation is a terrible design. – C. Lawrence Wenham Sep 5 '12 at 15:02
5  
Time is an illusion - Lunchtime doubly so. ;) – Wayne Werner Sep 6 '12 at 0:00
show 3 more comments

8 Answers

up vote 17 down vote accepted

As we cannot resolve arbitrarily small time intervals, what is ''really'' the case cannot be decided.

But in classical and quantum mechanics (i.e., in most of physics), time is treated as continuous.

Physics would become very awkward if expressed in terms of a discrete time.

Edit: If time appear discrete (or continuous) at some level, it could still be continuous (or discrete) at higher resolution. This is due to general reasons that have nothing to do with time per se. I explain it by analogy: For example, line spectra look discrete, but upon higher resolution one sees that they have a line width with a physical meaning.

Thus one cannot definitely resolve the question with finitely many observations of finite accuracy, no matter how contrived the experiment.

share|improve this answer
2  
I love discrete time, it's so much logical... – Yannbane Sep 5 '12 at 10:07
1  
is it in principle possible to construct an experiment to see if time is discrete or not. – user10001 Sep 5 '12 at 13:25
4  
@AlanSE: This argument is threefold buggy. 7000 times smaller is not yet arbitrarily small. And if you fly past something too fast, you cannot observe it anymore. Moreover, by assuming the laws of special relativity, you are already assuming continuous time. – Arnold Neumaier Sep 5 '12 at 15:58
2  
I don't really think a quantity that is not even in principle measurable can be said to exist at all. There is a unit of time that is small enough that it is not possible to measure anything smaller than it, even in principle. So I think that time might well be discreet. – Omnifarious Sep 5 '12 at 16:24
4  
@Omnifarious: That's not necessarily true. Suppose the smallest measurable unit is a quantity we call the "omnifarion". We cannot successfully measure anything smaller than 1 omnifarion; but maybe we can successfully measure π omnifaria, or √2 omnifaria, or some other irrational number of omnifaria. That would then imply that time isn't discrete: there's a lower bound to what can be measured, but there'd be no finite unit that every quantity of time is an integer multiple of. – ruakh Sep 5 '12 at 18:34
show 9 more comments
up vote -1 down vote

By the very fact of calling it time (i.e. assuming division), infinity appears as discrete. Otherwise, it is continuous. Same for space, since it's the other side of the same coin.

share|improve this answer
Please go into more detail about your assumptions and how they leads to your conclusions. As it stands, this doesn't really answer the question. – poorsod Oct 17 '12 at 22:20
up vote 3 down vote

The answer to this question is not known presently. Current physics is, as stated by other answers, based on fully continuous mathematical models, which particularly assume spacetime to be continuous. On the other hand you could argue that these models are isomorphic to discrete constructive models, with the general view that the continuous is the limit of the discrete. Some modern spacetime theories assume an underlying network/relational structure, and are fully discrete.

My personal belief is that continuous structures do not exist in the physical world. This is however just a belief.

See also: Is the universe finite and discrete?

share|improve this answer
up vote -1 down vote

Obviously space is continuous, so is time. What is not continuous is the conception of numbers which we are using in computers and measurments. There is no reason for something so fundamental to be descrete, since continuity is more general (and amazing) then discreteness.

share|improve this answer
Hmm, I'd need some argumentation. And personally, I like discreteness more than continuity. – Yannbane Sep 6 '12 at 20:14
Is your thinking process continuous? If so, so is universe and its time. There is always something inbetween descrete stuff, this emptiness makes whole system continuous. Descreteness is always embedded in continuity, since it needs a separator. – Asphir Dom Sep 6 '12 at 20:27
1  
That's quite contradictory. Also, you cannot objectively judge your thinking process. It might appear continuous, although neural activity does have steps, but that's not the proof that it is continuous. – Yannbane Sep 6 '12 at 21:47
up vote 5 down vote

I think it's important to note that quantum or quantized time is not equal to discrete time. For instance, we have "quantized" space. By this we mean that it receives quantum treatment. But the underlying coordinates still form a continuum. So even if you live on a finite circle and only consider wavefunctions so that you get a countable set of basis functions from which to form all the others, you can still in principle measure incidence of particles at any point, again forming a continuum. Therefore, if we take quantum time in analogy to quantum space, we would have to conclude that quantum mechanically it would still form a continuum.

Of course none of this proves how the universe really works, which is your question. The only honest answer direct to your question is "We don't know". Physical theories do not describe how the universe actually works, the only thing we know is that their predictions match experimental results we currently posses. So even if the best physical theories we currently posses use a continuum of temporal coordinates, we cannot by any means conclude that the way the universe actually works matches our description.

share|improve this answer
up vote 5 down vote

What you are talking about is similar to the problem of quantum gravity. Since gravity is an effect of the curvature of spacetime, to have a quantum theory of it, you need to quantize the spacetime manifold. This is done with spin foams which are little units of volume in spacetime that have spins associated to them. They connect together like total angular momentum and build up into various kinds of geometry. This is just a theory, but comes from the very real problem of "what is the quantum field theory of gravity". Also, it answers the question "Higher power is needed to resolve smaller dimensions (sizes). To resolve small enough distances, the power eventually gets large enough to couple to the metric of space time. How do we talk about spacetime when the uncertainty in the injected energy transfers to uncertainty in the metric."

share|improve this answer
up vote 0 down vote

My understanding of the fundamental issue of time is that if we base it upon physical transactions, then we are (not only) dealing with a discretized system (e.g. quantum interactions) - but that moreover time then may have geometric properties that further confound the question.

share|improve this answer
up vote 12 down vote

I'd say there's no conclusive evidence, but in quantum physics, Planck time is sometimes cited as a possible smallest unit of time.

The source for my data is Quantum Gods: Creation, Chaos, and the Search for Cosmic Consciousness by Victor J. Stenger. In there, he goes into a lot of detail about this in one chapter.

share|improve this answer
5  
From Wikipedia: Within the framework of the laws of physics as we understand them today, for times less than one Planck time apart, we can neither measure nor detect any change. So it's not necessarily the smallest unit of time, just the smallest one we're capable of using. – Brendan Long Sep 5 '12 at 14:34
1  
@BrendanLong - Except there's the philosophical question of "If there's no way to measure it, does it even exist?". Largely, for example, the answer for Heisenberg's uncertainty principle is that the information about a particles position and velocity don't actually physically exist simultaneously. So, if we can't measure a unit of time smaller than Planck time, if it's physically impossible, then perhaps it doesn't even exist. – Omnifarious Sep 5 '12 at 15:17
My interpretation of the Planck Time is that it's the smallest meaningful unit of time. Time itself is continuous, i.e. intervals shorter than the Planck Time exist. But these shorter intervals are trivial, so time may as well be discrete. Additionally, if time is discrete then distance as well must be discrete. It's weird to think of the universe as pixelated... – TestSubject528491 Sep 5 '12 at 23:25

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.