# Rate of time progression

We know time can dilate, but what about the base "rate" of how "fast" time progresses?

Is it even possible to conceptually pinpoint what time would be progressing relative to?

Some relevant points might be why we can't seem to go backwards in time without tricks like traveling really fast, which isn't FUNDAMENTALLY having time travel backwards. And if time travels forwards, at what "rate", if that is a valid question at all.

Let me give a little bit of background of where I'm coming from with this question.

It started when I was thinking about a universal standardized unit of distance, which would be based on the most universal and fixed thing we know of: light. light travels at X meters per second. If we have a standard chunk of time, we could take the distance the light travels during that time, divide it up by a round number like 10^10, and we would get a "light angstrom"

Now I thought I could do this for time, but I realized I just standardized my "light angstrom" unit of length relative to the unit of time we call seconds. So that got me thinking, "Time is like an independent variable... or is it?"

If we were to try to standardize a unit of time with another alien species based on something fundamental to the laws of physics rather than an arbitrary division of an arbitrary planet rotating an arbitrary sun, do we have anything fundamental and universal reference point to base it on?

Thanks for hearing my story. I hope it illustrates the question clearly, and where I'm coming from. It's a bit hard to communicate the question succinctly and frame it in the a succinct, abstract form.

• If you're just dividing the speed of light by a dimensionless number like 10^10, you aren't getting a "universal standardized unit of distance", since a speed divided by a dimensionless constant still has units of speed, not distance. In relativity there is no objective truth about which of two clocks in relative motion is ticking more slowly, likewise there is no objective truth about which of two meter-sticks in relative motion has a shorter length--different inertial reference frames will disagree on these questions. – Hypnosifl Oct 5 '14 at 22:42
• You're right about that. What I meant was lets take the distance light travels over a certain period of time. As long as that chunk of time can be standardized, then we can chop up that distance and whatever unit we get, that will be a unit that is "more standardized" to light, as opposed to the wavelength of a cesium atom or whatever other basis. Thanks for pointing that out. The relationship to time remains, and I'm wondering about that. – ahnbizcad Oct 5 '14 at 22:45
• But are you just asking whether we can find some natural units for proper time, i.e. time in the frame where a given type of clock is at rest? Or are you asking if there's some way to decide which of two clocks in relative motion is "really" ticking faster, relative to some sort of absolute time? If the former than sure, you can use something like cesium atom vibrations, if the latter then no, relativity rules out any measurable absolute time. – Hypnosifl Oct 5 '14 at 22:52
• – user4552 Oct 5 '14 at 22:56
• I mean proper time. separate from time dilation. – ahnbizcad Oct 5 '14 at 22:56

If we were to try to standardize a unit of time with another alien species based on something fundamental to the laws of physics rather than an arbitrary division of an arbitrary planet rotating an arbitrary sun, do we have anything fundamental and universal reference point to base it on?

Yes. For example, the second is currently defined according to an atomic standard, which aliens would be able to reproduce.

There is also the question of whether all clocks behave consistently with one another, to within their precision, if they're in the same place at rest relative to one another. Relativity requires that they do. If an experiment shows a violation of this principle, then it would be a problem for relativity. Experiments of this type are called clock comparison experiments.

An early experiment that can be interpreted as a clock comparison experiment was the 1960 Hughes-Drever experiment, http://en.wikipedia.org/wiki/Hughes-Drever_experiment . Section 5.2 of this review article http://relativity.livingreviews.org/Articles/lrr-2005-5/ describes some more recent results. Some good, recent examples:

Matsakis, Astronomy and Astrophysics 326 (1997) 924, http://adsabs.harvard.edu/full/1997A%26A...326..924M

Guena, Improved tests of Local Position Invariance using 87Rb and 133Cs fountains, http://arxiv.org/abs/1205.4235

As suggested by the title of the second paper, these can also be taken as tests of whether the laws of physics vary from one location to another.

• Are there other possible fundamental ways of measuring time besides vibations of atoms electron transmission? Or other atoms? – ahnbizcad Oct 5 '14 at 23:00
• Interesting how a second is pretty close to 10^10 periods (9192631770). en.wikipedia.org/wiki/Second Pure coincidence of course. Just for funzies, I calculated how long a year would be based on that kind of second. it's about 108.7% more, so that comes to about 397.1 regular days. Not suitable for earth. If we used 10^10 cesium atom vibrations, the speed of light would be 275 588 167.4 meters/"newsecond". – ahnbizcad Oct 5 '14 at 23:05
• @gwho: You are pointing out a significant problem: there is no "fundamental" way of measuring time (or anything else). We can only compare different types of phenomena against each other and we have to be careful to chose phenomena which are the least likely to suffer from uncontrolled systematic errors. – CuriousOne Oct 5 '14 at 23:25
• @gwho: By fundamental, do you mean reproducible by the alien species, in the sense of your question? Yes, there are other ways, e.g., you could use the frequency of a gamma-ray produced by annihilating an electron with an antielectron. – user4552 Oct 6 '14 at 0:03
• yes that's the nuance I mean by "fundamental". The energy is the same? If so, then it would be fundamental. But since it would be subject to misreading (red shift via universe expansion) I wonder if a good candidate would necessitate an additional requirement of being... preserved when read. – ahnbizcad Oct 6 '14 at 0:42