I suppose this could also be considered a thread for GD, but decided to post it here intead. It could, I suppose, have a factual answer as well as opinions; there probably isn’t a right or wrong answer. Anways:
Let’s assume that sometime in the [near or far] future, humans come into contact with an intelligent alien race, or more than one for that matter. What would be the most logical form of communicating the flow of time between our races? Lets keep in mind of course both linear and non-linear time. For example, the Earth makes an approximate 365 day cycle around our sun and we have 24 hours in each of those days, but we also are currently in the year 2003 C.E., next year with be 2004 and then 2005. It won’t ever go backwards.
I’d imagine without a working system, it could be rather difficult to ask another alien race to meet us on January 5th at 5:30pm when their sense of time could be moving at a certain fraction of ours, causing miniscule mixups that create larger problems (their form of ‘seconds’ goes by 0.009 or 1.06 times faster than hours). I have a feeling that all this could get a lot more complicated than I think.
And a side question: How exactly do the stardates work in Star Trek’s Federation?
I’m not sure what you mean by “non-linear time.” If you want to tell them how long our second is, you could just send a radio transmission saying “we define ‘second’ as the time interval between the next two beeps: beep…beep.” Doppler shift will cause a slight error, but not many planets are hurtling through space at relativistic speeds so it should be fairly accurate. If you need more accuracy you can correct for the relative motion by telling them that our planet is moving at such-and-such speed relative to the cosmic microwave background (CMB).
Or you can just tell them one second is 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. (from Wikipedia). That’s our definition of the second.
Once they know our unit of time (or we theirs), it’s just a matter of describing the calendar system.
I’m on the east coast, if i told someone in the central time zone to call me at 6PM, they would know to allow for the time difference… I dont think it would be hard to find a ratio for our different times
On second thought, I take back my comment about Doppler shift not being significant. It definitely needs to be corrected for, but there are many ways to do it.
Sure. But I think the best “event” for this purpose is a radio signal sent from one to the other. If the signal is then sent right back without any delay, this can also be used as a direct measurement of the distance between the two planets. And without the information about relative distance and speed you can’t synchronize your calendars and clocks anyway.
Not really. The emission has been decreasing slowly ever since the beginning of the universe but it’s such a slow decay that you can’t even measure any change, let alone measure the exact time it crosses some threshold value.
There is unfortunately no real simultanity between different parts of the universe if they are moving with respect to each other;
this doesn’t really matter if the populations of two or more space faring civilisations travel at slower than relativistic speeds; but if you travel fast enough to experience time dilation (or worse faster than light)
all hope of having a common time go out the window.
You could arrange to meet when the astronomical circumstances are right. If Mars, Earth, and Venus are in such and such precise alignment to Sol, and Earth is facing at such and such an angle, you have a unique set of circumstances that lead to one precise time (or at least unique within every gazillion years).
Or, you could define a certain arrangment of the planets to be time 0 (or Jan 1, 0 AD, or whatever), and both parties should be able to add up from there.
You could define universal time to be time measured in the ‘rest frame’ of the CMBR (i.e. the rest frame where the CMBR is not blueshifted in one direction and redshifted in another), coincidentaly that’s pretty much the rest frame of the Earth and you could have the units as divisions of the age of the CMBR measured from this frame. Though the laws of nature don’t have preferred refernce frames, sometimes nature conspires to produce reference frame that is ‘special’.
Okay, so we’ve managed to explain our time with another [one] race (kind of). Let’s look more into the future, which is kind of what I had in mind for the question, but I was half asleep when I posted it.
We have met… let’s say, 50 other alien races, and it’s been about 100 years since. Perhaps a diverse economy has grown between all of us, as well as politics etc etc… Correct me if I’m wrong, if you have a better idea, but there has got to be some simple way of telling time between us hasn’t there? Every planet could have their own time system of which they previously had, but add another “universal time” clock to the side of their existing ones.
IIRC, the Latin anno means “year of.” So Anno Fooius 0 means “zeroeth year of Foo.” I don’t know of too many instances outside of comp sci where people frequently refer to the ordinal “zeroeth.”
Julian dates and modified Julian dates are so much simpler to use, especially in hard science applications like negotiating with other-world civilizations, primarily because you then keep your time units to a few hard points:
Define time[sub]0[/sub] as some instance where time = 0. I like muttrox’s approach of using a planetary alignment.
Describe our scientific explanation of the second, as scr4 quoted.
Define 86400 (base 10) seconds after time[sub]0[/sub] as time = 1.0.
Match these to their equivalent of the second and “day.”
At this point, time references are straightforward to translate, and are left as an exercise for the interested student.
The second is currently defined (on Earth) 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 at rest at 0 C. The choice of spectral line is arbitrary, and we could as easily tell them the length of a second in term of an element and line of the spectrum that is convenient to them (though, if they are advanced enough to meet us anywhere, the convenience would be minimal)
Having transmitted a definition of a second (or “interspecies time unit” that we devise for the purpose) We then transmit a 1-sec tone. This will allow then to correct for doppler/time dilation effects between our two regions of space.
They can calculate the local effects of planetary motion and local gravity [they’d know their local conditions well] or disregard them - the effects are so small that even over a period of years, they would probably not add up to a full second.
Besides, if I recall correctly, the tardiness rule requires you to wait 10 minutes if an instructor is late, 15 minutes for an associate professor, 20 minutes for a full professor, and at least several for first physical contact with an entire alien species.
Once you’ve defined a unit of time, a simple message would suffice: “At the end of the 1-unit tone, the time will be 0. Meet us at <the specified location> in X units of time.” The physical definition of the unit is crucial to allow them to make corrections.
Oops, I meant to say “Meet us at <the specified location> in X units of time in our local frame.” (The correction in relative rate of time would be revealed by the 1 [physically defined] time-unit tone.)