# Lost time is never found again. - FranklinApril 10, 2014 10:00 AM   Subscribe

If time (as measured on Earth) were speeding up or slowing down (relative to what it had been in the past) would there be any way for us to notice or measure it?

Following a viewing of Cosmos and a conversation about Einstein, time, black holes, the speed of light and the passage of time, my son asked me this question and I promised I would try to get him an answer.
posted by anastasiav to Science & Nature (18 answers total) 2 users marked this as a favorite

Question: Error, undefined.

Is a second today equal to a second in the distant past?

Problem:
A second is an arbitrary unit of measurement, and is fundamentally intertwined with space. Your question is simply undefined. Measure a second now vs. a second then, but neither founded in anything.

Potential question rephrase (but probably not your true question):
If a second represents a fixed fraction of a day. And a day is calculated as a orbital cycle. Will the orbital cycle change over time thus changing the fraction of a day? Also could be asked as "will a day always have the same length on earth over time?"
posted by jjmoney at 10:08 AM on April 10, 2014

We have been watching the stars with relatively sophisticated measuring equipment for 50 to 100 years. We have cataloged our relative speed in relation to thousands of celestial objects. If time were to change, our relative speeds would change and this would be detectable as doppler shift changes between us and those other objects.
posted by gnossos at 10:10 AM on April 10, 2014

I mean, yeah, wouldn't you notice that your plants and trees were growing faster/slower?
posted by Melismata at 10:12 AM on April 10, 2014

We can talk about time passing slower for one object relative to another - an object traveling near the speed of light will experience time slower than an object at rest, but without some comparison point the question doesn't really make sense.

It's kind of like asking is the entire universe further east than it was before.
posted by aubilenon at 10:13 AM on April 10, 2014 [2 favorites]

Speeding up or slowing down in what way? Would all timepieces suddenly be reporting a slower time on earth, but if they were on one of Saturn's moons, they would be reporting how we saw time before the change? If that was the case, things like the speed of Jupiter's moons would observably change. (I'm thinking of Jupiter's moons because one of the first attempts to measure the speed of light used them.)

Also, if I'm picturing this properly, the wavelength of light received from everything not on earth would be blue shifted, although I might be picturing the doppler shift in the wrong direction.

Ted Chiang's short story Exhalation (pdf), while really about entropy, also addresses the idea of a slowing down in the perception of time.
posted by Hactar at 10:15 AM on April 10, 2014 [3 favorites]

This is essentially asking what is the speed of time, which just doesn't make sense. Or, how many seconds ago was one second ago? There's just no such measurement.
posted by kiltedtaco at 10:16 AM on April 10, 2014 [1 favorite]

iirc, a second is now defined as a certain (high) number of state changes in a particular atom (cesium?). the onus would be on the proponent of a claim that atoms have speeded up or slowed down their state changes.

your son asked you a smart question. if you are judeo-christian with an old testament in your house, you could show him where methusaleh lived to be 969 years, and ask him if one possible explanation would be a different speed of time. again, the onus is on the proponent, but there were giants in the earth in those days...
posted by bruce at 10:52 AM on April 10, 2014 [1 favorite]

The short answer is, you find something that acts like a clock and then you check to see whether one thing that acts like a clock changes relative to something else that acts like a clock, given different situations.

That's the sort of thing that experiments to verify the theory of relativity do, so you might look at, for example, this article listing different ways that the general theory of relativity have been tested. You'll notice that a number of them involve things that 'act like a clock' by being predictable over time, like the orbit of Mercury, the orbits of binary pulsars, the pulsar themselves (they emit very regular pulses, thus their name). The relativity examples are a bit more complex because they are all looking at space-time, not just time itself. But still, the general ballpark of the idea you're looking for.

Another nice example is the decay rate of various particles. Decays rates for certain particles are well known and are something that 'acts like a clock'. Here is a nice test of special relativity that depends on this, for example.

For more examples, look at some examples of experiments that confirm time dilation & contraction under special relativity.

In short, it is quite possible and even quite common to be able to demonstrate that times runs at different rates in different situations.

It's going to be harder to do with things in the past vs the present just because because we can't directly go to the past and experiment. But still, you start looking for things that 'acted like a clock' in the past, and that we have a record of, and compare them to similar clock-like things still operative today. That seems like it would be hard or impossible, but it is the basis of whole fields of archaeology--everything from tree-ring chronology to radiocarbon dating. Overview here. I don't know of anyone who would study this specifically to find, say, time dilation differences between the earth a million or a billion years ago and now. Partly that is because physicists feel like they have a good handle on what those differences would be like (super-subtle), what would cause them (things like relativity that are far easier to study in different ways), and the tools we have to measure earth-time on those scales, like potassium-argon dating, give relatively coarse results relative to the super-subtle effects you would be expecting.
posted by flug at 10:52 AM on April 10, 2014 [7 favorites]

an object traveling near the speed of light will experience time slower than an object at rest, but without some comparison point the question doesn't really make sense.

C'mon guys, he's 7, and he's asking this in good faith.

To clarify a little (as much as I can): we read the time dilation entry on Wikipedia, which talks about how clocks on the space shuttle run (ran) slower than reference clocks on Earth, but in that case we are the reference. Now, he also knows that the universe is expanding. So, I believe his question is that, were it true that our entire solar system was accelerating as it moves outward, and time was passing faster now vs. 60 million years ago, would we have a good way to measure that using some kind of extra-solar-system reference point.

On preview: flug gets the basic concept behind his question, and so do a couple of other answers. Thank you for taking his thoughts seriously.
posted by anastasiav at 10:57 AM on April 10, 2014

Decays rates for certain particles are well known and are something that 'acts like a clock'.

Actually, radioactive decay rates fluctuate with seasons. Fluctuations were initially attributed to bad measurements, but now it is understood to be a real phenomenon, though physicists aren't sure how the Sun is a causal factor.

I used to believe radioactive decay rates were one of those immutable things that go on in the universe, so I was surprised to learn it isn't true.
posted by Blazecock Pileon at 11:08 AM on April 10, 2014 [1 favorite]

Yes there would be ways of finding out that time on Earth was speeding up or slowing down.

I think the best might be observing pulsars, as indicated by flug.

All pulsars, as far as I know, are slowing down, though some of them have such consistent pulses that, according to the linked article "certain types of pulsars rival atomic clocks in their accuracy in keeping time."

If time only on Earth were to suddenly start speeding or slowing, we would notice that the timing on the pulses of all the pulsars we observed would also start speeding or slowing-- from the values we had come to expect and be able to predict from previous observation-- in the same way no matter what pulsar we looked at, and that would tip us off that our own time standards were moving for some reason.

If time on Earth had always been speeding up or slowing down at the same rate, we could also in principle deduce that from pulsars, because in the case of time slowing on Earth, some pulsars that were in actuality slowing down at a very, very low rate (lower than the Earth rate) would seem to be speeding up; and if Earth time had always been speeding up, we'd observe that all very regular pulsars had a surprisingly high and identical rate at which they started slowing down.
posted by jamjam at 11:29 AM on April 10, 2014 [2 favorites]

In order to talk about time slowing down, you have to have some sort of a clock. We have lots of different clocks, and they don't always agree with each other; whether you choose one clock over another or conclude that time itself is behaving strangely is one of the core pieces of special relativity.

Keep in mind that when I say "clock" I don't necessarily mean a mechanical thing that ticks; I mean any natural phenomenon that recurs occasionally. You decide if your recurring phenomenon is a good clock by comparing it to ... other clocks! This means that if you only have one sort of clock, you can't make any judgement about whether it keeps "good time" or whether it sometimes runs faster or slower.

Our calendar is based on three naturally-occurring clocks: the rising and setting of the sun, the changes in the phases of the moon, and the changes in the location of the sun as we see it against the distant stars. These give us the day, the month, and the year. Now if you use your eyes and a calendar to keep track of the moon and the stars (which a 7-year-old could do, with guidance), you'll notice that there are almost exactly 30 days between full moons, and almost exactly 360 days in a year. These are nice round numbers with lots of divisors, very easy for doing arithmetic. You have to be quite a careful observer to do much better than this: a thirty-day "moonth" takes most of a year for the phase of the moon to slip by a week, and a 360-day year takes most of a decade for the solstices to slip by a lunar cycle. Now imagine that you are a practical-minded, pre-modern person who doesn't care much for the stars but wants to know when the spring rains will come, flooding your river and moving the herds and letting you start this year's planting. These environmental "clocks" have much more variation from year to year than the astronomical "clocks," but which set of clocks is "better" depends on your perspective.

One answer to your son's question, then, is that there haven't always been 365.24 days in a tropical year. There are several lines of evidence that indicate there were once more days per year than there are now: friction between the oceans and the land due to the tides is stealing rotational energy from the earth, slowing it down.

Aside to Blazecock Pileon: In my professional opinion, the evidence for seasonal variations in radioactive decay rates is quite shaky. Give it a few more years.
posted by fantabulous timewaster at 12:14 PM on April 10, 2014 [1 favorite]

Sorry for the previous response. The extra-solar reference point is key - without it, yeah the question doesn't make sense. But with it, sure!

If time only on Earth were to suddenly start speeding or slowing, we would notice that the timing on the pulses of all the pulsars we observed would also start speeding or slowing-- from the values we had come to expect and be able to predict from previous observation-- in the same way no matter what pulsar we looked at, and that would tip us off that our own time standards were moving for some reason.

You don't need pulsars to do this. The light that all the stars are emitting is also a clock. If our passage of time changed relative to the stars, we'd see all the light suddenly shift towards red (if we sped up) or towards blue (of we slowed down). I'm not sure if we could distinguish this from the rate of expansion of the universe suddenly changing, but we would for sure notice it.

We've been measuring and studying stellar spectra since the 1860's or so.
posted by aubilenon at 12:45 PM on April 10, 2014

So, I believe his question is that, were it true that our entire solar system was accelerating as it moves outward, and time was passing faster now vs. 60 million years ago, would we have a good way to measure that using some kind of extra-solar-system reference point.

It may be important to note (and they did note it on Cosmos), that there is no center of the universe like most people imagine. Space is expanding from every point. The solar system is not moving outward as a unit from some central point, but rather every point in space inside of it is expanding.
posted by Thoughtcrime at 1:44 PM on April 10, 2014

The answer to your son's question is a qualified yes, we would/might be able to tell.

His question is actually a very good one. For example, there are a few things we can define as "fundamental constants", and other quantities being measured against those. There is something known as the fine structure constant which people have thought, like your son thought about time, might have changed over time, or might have had different values in different places in the universe. Careful measurements from events that took place in a naturally occurring nuclear "reactor" here on Earth millions of years ago, as well as those occuring on distant stars which we see now (and were produced millions of years ago) show that this constant had the same value "there" as it had here.

So, you can tell him that his question is a very good one and that we don't know currently have any evidence that it has changed, nor do we have any reason to think that it should have changed.
posted by aroberge at 4:20 PM on April 10, 2014

Actually, jamjam and flug gave very good answers - probably better than my own.
posted by aroberge at 4:23 PM on April 10, 2014

Space is expanding from every point.
IIRC, It's just the space between galaxy clusters that seems to be expanding
/derail

I assume he means if time everywhere were speeding up and/or slowing down would we notice?
The simple answer is no, probably not.

The complicated, and very fun, answer involves Simulation theory...in a nutshell, we, as an intelligent species tend to make models, or simulations, of our environment...weather maps, video game environments, globes, etc...and as the number of these simulations within our universe goes up, the likelihood that we live in the real universe goes down. (Many scientists also point to the quantuum nature of time and space, i.e. that it is not a continuous flow, but instead comes in discrete units, the Planck unit (approx 10^-43 of a second), as evidence that we do indeed live in a computed simulation where the Planck unit is the clock speed of its 'processor')
Ok, here's the cool part: It's possible to put larger universes inside of smaller ones. Here it becomes handy to think of resources...say, for example, that you are able to create perfectly 100% efficent simulations where one atom in your universe is used to simulate one atom in your simulation...a 1:1 ratio. It would then require the entire contents of your universe to create a simulation of it (there's a Steven Wright joke about this..."I have a map of the United States. It's actual size. Maybe you've seen it?") But what if you ran the simulation slower? If you ran your simulation at say 1/10th speed, then the atoms required to run it could work in parallel and it would only require 1/10th of the atoms in your universe to make it work and you would have a full-sized universe that only takes up 1/10th of the space of the universe that it's inside of. AND, if you are inside of the simulation, since that is your entire universe, there's no way to tell that it's running slower, since it's all running at the same speed.
So yeah, it could very well be that someone outside of our universe is fast-forwarding or rewinding it or running it in slo-mo all willy-nilly (or it could just be sitting on a tape on a shelf) and there would be no way for us to know. Goodnight, sleep tight. :*
posted by sexyrobot at 6:34 PM on April 10, 2014

Space is expanding from every point.
IIRC, It's just the space between galaxy clusters that seems to be expanding
I don't think there's evidence for or against this? The Hubble constant is roughly 75 km/s per megaparsec; at the location of the Andromeda galaxy, roughly one megaparsec away, the Hubble expansion is slower than the typical motions of the stars around the galactic cores, and also slower than the motions of the galactic cores with respect to each other. It's impractical to separate the motions of objects within space to the expansion of space, so I think that we can't know whether our local space is expanding or not.

posted by fantabulous timewaster at 8:43 PM on April 10, 2014

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