In modern physics, or at least its non-mathematical version for laymen, we hear of time's "going slower" or "faster." In the rocket experiment for the Twin Paradox, for example, time "went slower" for the traveling twin than it did for the stationary.

But the result of that experiment, so far as I could tell, could also be described as "fewer events occurring" (because at lower frequency) for the traveling twin (while time went at the same speed for both twins). For example, a quark in the traveling twin shook (I don't know if quarks shake or jump) only 100 times while the corresponding quark in the stationary twin shook 1,000.

Which of the following is true?

Modern physics

  (a) could speak either way, but chose the terminology of time's variable speed for mere convenience.

  (b) must stick to time's variable speed because some types of results (not included in the rocket experiment) support it and not variable frequency of events.


I am adding this bit in response to the "hold" notice, which states that "it’s hard to tell exactly what you're asking."

Please see if the question becomes more intelligible as read in conjunction with Andrew Steane's comments, which I replicate here:

The term 'time dilation' is indeed sometimes confusing or misconstrued. The bottom line is that, between separating and meeting again, the rocket twin has fewer heart beats, fewer wristwatch ticks, fewer caesium atom oscillations, fewer cell divisions, etc. etc., and all by the same factor compared to the other twin. You can call it what you like, but it is not a conspiracy.

Those comments answer the question to my satisfaction, and therefore I do not need more answers. I only add this bit for the benefit of those who might care to understand the question.

To characterize the question somewhat differently, it asks whether, having said 'fewer heart beats' etc. (in the sense above), i.e. having made certain statements about events, you need to make an additional statement about time (e.g. its 'dilating') to complete the description of the test results.

Suppose the answer is no, i.e. that you need not make any additional statement about time to describe the results of the experiments. Then you really need to examine the facile (not to say fanciful) idea that these experiments are telling you anything about the nature of time. On this page alone, you will find the tendency to think that a statement about time is a mere equivalent to a statement about events. That may turn out to be true, but would not be trivially true, and probably would not come out true or false as a result of these experiments. In other words, the question goes to what these experiments are about (as well as what not).


closed as unclear what you're asking by WillO, Buzz, John Rennie, ZeroTheHero, Jon Custer Jan 28 at 17:17

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ (c) Modern physics does not talk about time's "going faster or slower" for exactly the same reason it does not talk about time's changing color. I.e. we try to avoid speaking nonsense. $\endgroup$ – WillO Jan 25 at 19:01
  • $\begingroup$ @WillO. If you prefer, we also get "more" time having elapsed for the traveling twin, time's having "dilated," etc. I am asking whether all that talk could be replaced with merely all events speeding up or slowing down instead, leaving time alone--because yes this talk about time does sound like nonsense. $\endgroup$ – Catomic Jan 25 at 19:06
  • $\begingroup$ how are they mutually exclusive? slower speed indeed implies fewer events, and viceversa. Evenys are just points in spacetime. $\endgroup$ – Wolphram jonny Jan 25 at 19:45
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    $\begingroup$ The term 'time dilation' is indeed sometimes confusing or misconstrued. The bottom line is that, between separating and meeting again, the rocket twin has fewer heart beats, fewer wristwatch ticks, fewer caesium atom oscillations, fewer cell divisions, etc. etc., and all by the same factor compared to the other twin. You can call it what you like, but it is not a conspiracy. $\endgroup$ – Andrew Steane Jan 26 at 16:46
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    $\begingroup$ @AndrewSteane. Ah, thank you! That's exactly the answer I hoped I would get. When I heard time dilating, speeding, repeating, etc., etc. I thought why, science wants to be poetry! $\endgroup$ – Catomic Jan 26 at 16:56

Time is typically viewed as a continuous variable, not a discrete one. We may measure it using discrete means, such as "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" (which is how we defined the second in 1967), but it is always viewed as a continuous concept. (Discrete time is something that comes up on the Plank scale, but is a very difficult to pin down concept. It also appears in philosophy, where it is equally if not more difficult to pin down with things like A series time and B series time...)

This means that if I have a whole hodge-podge of different frequencies of events that I'm paying attention to, I don't have to think in discrete terms. Every one will be adjusted in a continuous way in a manner which is consistent with "time moving faster". If I have photons streaming about and physical masses moving in a way modeled by Lagrangian mechanics, I don't have to worry about how to combine them meaningfully: they use the same continuous time variable which appears to be going faster.

At some point, there's a duck argument to be made. If it looks like a duck, and quacks like a duck, then it's probably a duck. In physics, every which way we have explored relativistic effects has demonstrated behaviors identical to those we would see if "time went faster." At some point, we just start skipping the words "identical to the effects of time going faster" and just say "time went faster."

  • $\begingroup$ It seems to me you are giving me (a). That is, if somebody wanted the inconvenience of having to say, 'x went faster, y went faster, z went faster, but time remained constant,' nobody could call that less right than time's having gone faster. Do I understand you right? $\endgroup$ – Catomic Jan 25 at 18:58
  • $\begingroup$ @Catomic That is actually how relativity started off. Maxwell's equations ran into trouble with reference frames, and the resulting correction factors were a complete mess unless you permitted the flow of time to change, then they became a minor mess. They then stopped being messy at all when relativity proposed that spacetime itself was stretched by velocity. But if you want, you can go back to the original horrible equations and predict the same results. $\endgroup$ – Cort Ammon Jan 25 at 19:27
  • $\begingroup$ Which one is ontologically correct is another topic entierly, and one it turns out science doesn't have a firm grip on, though it's rarely taught as such. $\endgroup$ – Cort Ammon Jan 25 at 19:28
  • $\begingroup$ I am glad you speak of ontology. That is nearly my concern; or that, if one way of speaking is merely troublesome and the other extravagant, then the respectable thing to do is to take the trouble. If you take the easier expedient, then you'd better disclaim loudly: "I don't pretend to have discovered anything about the universe. It's only convenient talk." (You, of course, being science.) $\endgroup$ – Catomic Jan 26 at 3:53
  • $\begingroup$ @Catomic I have struggled with that for some time, so I feel you there. The rationale I rely on today is that science is incapable of making justified ontological claims. Everything in science is in the form of a hypothesis that has not been proven, it merely has not been disproven when we threw all the experimentation we could at it. As such, that little bit of doubt that is required for pure intellectual honesty gets sort of bundled into the language. If someone speaks in the language of science, they must speak with that little bit of doubt implied. $\endgroup$ – Cort Ammon Jan 26 at 4:03

In modern physics, or at least its non-mathematical version for laymen, we hear of time's "going slower" or "faster."

You said it. Physicists never talk of time going slower, nor of clocks slowing their march. And mathematics has nothing to do with it - the issue is exquisitely physical.

In some past answers of mine, about the same subject, I declared that I really can't even understand what "time going slower" could possibly mean. Before of being right or wrong.

There is another reason why such phrase should be avoided. If you introduce two "observers", say A and B, and say that B's time goes slower than A's time, it's logically unavoidable that you must also say that A's time goes faster than B's. And this is in patent contradiction with relativity principle, stating that all inertial observers are equivalent.

Your proposal of "fewer events occurring" looks to me completely equivalent. Moreover it has another drawback: in common physical understanding an event has an objective character, it happens independently of any observer. So also your proposal is out of my understanding horizon.

To me there is only one way out, consisting of an accurate choice of terminology. It amounts to two precepts:

  • Leave aside observers. Speak instead exclusively of reference frames (shortly "frames").

A frame has nothing to do with someone observing, viewing or else. A frame is (put simply) a physics lab, endowed of all required instruments - in our case, first of all, of a battery of synchronized clocks, resting in that frame and ideally located in every point of space. By these clocks every physicist in the universe may be informed of the time (as recorded by that clock) a particular event happened in its immediate neighbourhood.

So I introduced the second precious word: event. The second precept sounds

  • When you talk about time, you are always talking of time associated to a particular event.

The basic point is that an event is independent of observers and also of frames - it happens and that's all. Instead the time associated to an event is relative to a given clock, one resting in a given frame. Nothing forbids to measure - for the same event - times relative to two or more frames, i.e. measured with one or the other set of clocks. There is nothing like an absolute time an event occurs.

If you have two events, it makes sense to ask for the time interval between them, but the answer is relative to the frame. In particular, it's often of interest to know the time interval measured in the one frame where both events happen at the same space location (if there is one). This may called, if you like, the proper time interval.

One fundamental result of SR is that among all time intervals between two given events the proper interval is the shortest. This and only this is the meaning of the common expression "time dilation". It exactly means this:

  • Given two events E and F the time interval between them, as measureed from a generic frame K, is always longer than their proper time interval.

That's all. No time going slower, no clocks retarding, no different number of events occurring (as you'd like to say).

I hope this helps, but I'm sadly aware that the same question will be reiterated again and again. I'm afraid that centuries will have to lapse before humankind may arrive at a diffused consciousness of the real facts about time.

  • $\begingroup$ Thank you. If I may put a clarifying question, do you mean that "fewer events" necessarily drag in (imply) an observer? If so, could you explain why? I only meant that the rocket experiment might be described with, "The traveling twin's heart beat 100 times and the stationary twin's 1,000 between their parting and reunion." (You will note that I never had to mention time.) I intended that as a fact, never mind any snooping observer. In just the way that "There is one egg in this basket, and there are two in that" might be a fact. Thank you. $\endgroup$ – Catomic Jan 26 at 16:52

Here (at the black dot) is my Lower Slobbovian friend Alice, looking northward at the Upper Slobbovian border, 1000 miles straight ahead. (The blue line is her line of vision.) Now she turns so she's facing northeast, and finds that the border is now 1414 miles straight ahead (along her new red line of vision).

enter image description here

Here is the (exact!!) analogue to your question:

According to modern physics, when Alice turns to the northeast, distances in the straight-ahead direction are magnified by a factor of 1.414. But we could equally well say that when Alice turns, there are now more locations between her and Upper Slobbovia. Which of the following is true:

a) We could speak either way, but we always choose to say that the distance increased because this is a convenient terminology


b) We must speak in the "variable distance" language because some phenomena not mentioned here support it as opposed to the "more locations" language.

If your answer to this question is a), then the answer to the question in your original post is a). If your answer to this question is b), then the answer to the question in your original post is b). If your answer to this question is: "Huh? Modern physics says what?", then that is the answer to the question in your original post.

  • $\begingroup$ Thanks for the offering, but consider: How can three things be an analogy for two things (never mind exact)? In question in the original rocket experiment is the (as it were) temporal distance between two things, viz. the twins' parting and their reunion. It is supposed to be strange that either (e.g.) two or twenty years has elapsed between these two things depending on whom (which twin) you ask. In Alice's case you have three things. To see this, only imagine that the border is a river, which a drought as cut into two ponds (located where the blue and the red lines meet). $\endgroup$ – Catomic Jan 26 at 9:55
  • $\begingroup$ It is not strange at all that the Alice-pond 1 and the Alice-pond 2 distances should be different. Pray, where is the analogy? Of course, modern physics might have some fancy idea by which the two ponds come out being (numerically) identical, but you have to build that into the river case if it wants to be an analogy. I grant that your main point does not depend on any analogy, at least the way I read it. It is that "far" just means "more location between." $\endgroup$ – Catomic Jan 26 at 10:19
  • $\begingroup$ But the relation between "far" and "locations" is not the same as that between "long" and "events," at least not obviously. You'd really need to argue for the thesis that there is no conception of duration apart from events, which may succeed or fail. Indeed the rocket experiment etc. may argue for the availability of such independent conception. (I realize this last statement must be totally opaque.) $\endgroup$ – Catomic Jan 26 at 10:28

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