# Time on other planets

Back to the basics, science simply for science’s sake.

On Earth, we have time zones, as everyone (mostly) knows. These time zones are based on the sun, as is our entire time measurement system. Since this measurement of time is based on the position of the earth relative to the sun, its rate of spin, and its orbit, does time exist on other planets? I would assume so, but it is a rather puzzling question.

Take the moon, for example. Much smaller than Earth, and turning at a different rate. Is there a system for measuing time on the moon? Is there such a thing as “moon time”? How would time zones work there? What about Saturn?

Of course, we meaure time based on the Earth and the sun, and that just makes sense, since this is where we live. If we measure time on other planets based on our Earth system, though, does that assert that we are central to the universe? Does that mean we still think we are somehow special? Is there such a thing as Universal Time?

Take it one step farther, and ask whether time exists at all. Is it a synthetic mechanism, or does it exist, and we just interpret in our way.

IF there is life elsewhere in the universe, how would they measure time? When humans begin travelling in space over long periods and distances, how will we measure time then? If a planet that has sentient life has a year based on its orbit, and that equates to 500 Earth years, aren’t we going to be confused when they tell us that they visited us 10 years ago, on a global scale?

Actually the moon doesn’t rotate (Don’t quote me on that. Feel free to correct). Oh, and if you think about it, time doesn’t exist. It is just something we have created to make things more convenient. If we are what could be considered “singular dimensional creatures,” then that further supports my theory…that would mean that everthing that has happened, and will happen, and is happening is happening simultanously(Read that again if you need to, feel free to correct my inaccurate spelling).

Time measured in seconds, hours, years, and centuries is based on a variety of local factors alone, as you’ve pointed out. Rotation of the earth, its orbital path around the sun, etc. If you’re asking if time exists on other planets, compare time to distance. Distance exists on other planets, but until we define it as “feet” or “meters,” it doesn’t make much of a difference – it’s all relative. Measuring time is more difficult if one was to crash on a strange planet, as our perception of time is based on local conditions. Human biological cycles would probably give an idea of the passing of time, but that’s probably the only way you could tell on your own.

As for “absolute” time, some things are constant no matter where you are in the universe (within your reference frame), such as the half life of Uranium-235. The half life will always be the same. I suspect that if we meet forms of alien life and can communicate, that is the type of time we will use (i.e. “we first ventured out into space “x” half-lifes of Uranium-235 ago”). Or, if they are “local” aliens, we could use the rotation of our galaxy as a time frame as well.

-Psi Cop

Sure time exists. An intuitive definition would consider time as representative of increased entropy in a (relatively) closed system.

A different definition would be required by quantum mechanics, but there’s time there too. And it ain’t measured in seconds. For some particles (the kaon?) time is very important, especially the direction of it. whereas a photon could care less which way time flows, a decayed kaon would care, as it is not a time-symmetrical particle (last I checked).

Moon rotation

Special? Only in as much as we are only talking to ourselves, so it is easy to use conventional references to time.

I don’t think there would be universal time… though I suppose one could make galaxial time.

It’s rotation takes 27.322 days, the exact amount of time it takes to revolve around the Earth. That’s why the same side is always facing us.

Er…

Oops. Too late.

You will soon learn that this is a phrase you will never need to type around here.

Seriously, the Moon’s period of rotation is (more or less) equal to its period of revolution around the Earth. This is why we only see one face of the Moon, and why it has a “near side” and a “far side”. (Try walking in circles around a lamp or something and you’ll see what I mean.)

Well…it’s been experimentally verified that all physical processes–atomic decay, and, we have every reason to believe, chemical processes, including metabolic processes and therefore things like aging and thought–can be slowed down relative to a different frame of reference. In other words, the old “twins paradox”–one twin travels to some distant star and back at nearly the speed of light’ when he returns to Earth, he’s still young, but his stay-at-home brother is an old man. That indicates to me that time is something other than just a human semantic construct.
As to the OP: On a world like the Moon, where the “day” is 28 Earth-days long, I doubt people would ever use anything other than Earth time. (“Universal Time” is basically a fancier version of Greenwich Mean Time.) If humans ever settle Mars, which has a day which is almost, but not quite, the same length as ours (about 30 minutes a day different from our day), they might devise some interesting “local time” of their own. And the Martian year is roughly two Earth years, so their calendar might look quite different from ours as well.

And erislover wins by a nose!!

That was on the “moon rotation” thing, of course. Others were, admittedly, more robust.

I think it was that “Feel free to correct” thing. That’s like walking around the Serengeti wearing “Eau du Crippled Gazelle” aftershave and a toupee made of raw hamburger.

If space aliens get as far as being able to communicate with us in English, petty little details like time units will have already been well taken care of.

Anyway, everybody knows that the aliens say things like:

“We last visited your planet 500 of your primitive earth ‘years’ ago”

Yeah, advanced spacefaring civilizations use “yarins”.

Or “parsecs”.

Actually this OP is best asked of a Scientologist, since scientologists have lived on other planets during their past lives.

See Kim Stanley Robinson’s excellent book Red Mars for a possible manner in which we might accomodate the Martian day and year.

How exactly do aliens use parsecs to measure time if they’re

a. just as artificial as seconds and hours (IIRC, it’s the distance at which the diameter (or radius?) of the Earth’s orbit takes up one second of an arc…) and
b. not actually a measure of time at all?

The cause of the confusion is we call “time” two different (but slightly related) things: Universal Time (UTC) and our own local standard time. (In Spanish it is even more confusing as they use the same word, “tiempo”, also for the weather).

The preference for using time zones can only be explained historically by the slowness of communications but it makes no sense and things would be much easier if we all used UTC.

A similar thing happens with the seasons between the two hemispheres and we do not say it is now April in Argentina. It is October for everybody even is it is Autumn for some and Spring for others.

Similarly, universal use of UTC would make things simpler but people cannot get used to the idea that the sun would rise at 5 pm where they live.

The simplest answer I’ve heard for the question “what is time?” is that it is the measurement of change. This is, most likely, just a simplified verion of the entropy explanation.

Anyway, there is, as far as I know, no place in the universe where change does not occur. Something is always happening, even if it’s simply the movement of a single photon from one place to another. By such reasoning, time exists everywhere.

What units are used to measure time are complately arbitrary, as are any other units to measure anything else. Gram, meter, second? All of 'em are just an agreement between people to use the same measurement to mean the same thing. If there were anything not arbitrary about them, we wouldn’t have a need for an international standard - it would be written into the entire universe.

As far as Great Debates go, this one could be a doozy. A friend of mine used to say the Metric System was inherently easier than the system of wieghts and measures we tend to use in the U.S., because “dividing things by ten is simpler.” A challenge of this was easily shown by asking him to show me where 1/16th of a meter-long string was, without using any other measuring device. His divide-by-ten argument was soundly routed by just folding the string in half four times. On the other hand, I couldn’t show him 1/10th of the string just by folding, but he couldn’t show it to me either, without guessing.

So yes, time exists. What we, or any other lifeforms, choose to use to measure time is up to endless debate. But if you find some extraterrestrials, you might want to ask 'em what they really mean when the word “year” pops out of your Universal Translator.

I concur with DaveW. Time and distance are abstract concepts without a common frame of reference. I have before asked myself, “Was there time at the beginning of the universe?” and invariably I answered, “Of course. It’s just that there wasn’t anybody around to call it that.”

This discussion can easily stretch out for a while … which leads me to say that some people might feel better about time on other worlds if they only used ambiguous colloquialisms like “I’ll see you soon”, “Meet me later” and “Y’all come back now, ya hear.” I reckon whoever is on said laid-back planet would get used to the general spans of “time” each of those meant and it would actually work out.

Hmmm, gotta see if I can start coming to work “In the morning.”

Yeah, that was a joking reference to an (in)famous line in Star Wars in which Han Solo brags that the Millennium Falcon has made the run to Kessel in “less than 5 parsecs”. Of course, using parsecs as a measure of time makes about as much sense as using feet as a measure of time. A parsec is the distance at which an object will show a parallax shift of 1 arsecond, with the diameter of the Earth’s orbit as the base–i.e., you observe the star in July, then when you observe the star again in January, it will have shifted against the more distant “fixed” background stars by 1 arcsecond. That distance is about 3.26 light years (there aren’t actually any stars that close; the Alpha Centauri trinary system is over a parsec away).

“Yarins” are what they used on Battlestar Galactica instead of “years”. I don’t know if that’s actually how it’s spelled; it’s bad enough I know the word–I try to cling to some remaining shred of dignity by telling myself that at least I’m not sure of the spelling.

Hey, in God’s units, lengths and times are the same thing! It’s only all these silly conventions that we’ve built up over millenia that make them different. (Or at least, that’s the way physics people rationalize things.)