How to determine the time period.

[eptheta]

Suppose I found a time machine and clicked the 'go' button, and landed up sometime in the future. I then meet a bunch of humanoid creatures and manage to communicate with them.

I ask them what year it is, but they just tell me it's 1050 after the death of the 'mighty one', indicating that no one follows our nice date/time system anymore.

I could just be to them, what the dinosaurs are to us, a pre-historic creature, and they have no records of an organism of my kind existing.

I know this is earth, what is the easiest way to estimate how far in the future I am ?
NOTE: This is not a riddle or anything, just a question.

Thanks.

 

[justPAB]

Since you're in the future, you would have to use a technique similar to carbon dating. We need an organism from our own time era, so I guess you'd better take a dead animal or something containing carbon so you can calculate the carbon 14 isotope decay; hence giving you the estimated age in the future.

 

[eptheta]

Any way perhaps by tracking stellar orbits with telescopes ?
(and I can't do carbon 14 dating on something i carry with me in the time machine, it will stay as un-decayed as when i brought it aboard, i need 'find' something from my era in the future, an impossible task)

 

[justPAB]

in that case, back to the drawing board lol

 

[Andre]

Maybe, find out the average distance to the moon as it recedes about 38mm/year.

 

[eptheta]

Assuming that I travel into the future say 200 million years, (to make 2010 seem like the Jurassic age) that would make the moon move...7600 km away. That's a noticeable difference, nice !
I guess that could work ! Great!

Also,in a similar context, if you time the length of day 200 million years in the future, it would be 1.27 hrs longer. I guess that could work too if you time sunrise to sunrise.
Seems easier than calculating the distance to the moon, but a much smaller range to work with...What's interesting is that if the universe survives for a mere 1.36E12 years more, there would be only 1 day in a year of 8760 hours...
Any other way anyone can think of?

 

[billiards]

Measure the age of the Earth -- using Uranium isotope ratios or something (or you could just read it on Wikipedia if they still have scientists and wikipedia then) -- and see how much it differs from the 4.5 billion years we have today. That would be good for really long leaps forward (more than 100 million years), but the resolution is not very fine so not good for less than that.

How about looking at the continents... how much have they moved? What was the spreading rate before you left? Of course, ideas like that (and the moon idea) are probably not very reliable over long distances of time, because the rate of drift is likely to change with time -- perhaps we would need to factor in the second order term of acceleration to improve our estimates...?

 

[eptheta]

the thing about decay is that you need a source of materials to compare to your reference value.

Whats to say that one can find the same uranium source that one left 200 million years ago. Continents shift, sea levels rise and fall, ice ages come and go. That's why I'm guessing i'd need something that is constant and always will be constant.
Or is this ratio method you speak of using uranium isotopes in the Earth's crust that have always been there ?

From the looks of it, the moon's distance is constant. In the wikipedia article it said that it is estimated that the Earth had 400 days of 21.something hours each 410 million years ago. If that observation is true, then it seems sufficient a source to make observations on.

 

[Andre]

... Of course, ideas like that (and the moon idea) are probably not very reliable over long distances of time, because the rate of drift is likely to change with time --

Very true, but maybe the variation in drift of the moon is a bit predictable when it's understood how it works. I would think that the reduction in gravity force at greater distance would decrease the rate of drift. Also with the drift, the orbit time will increase, which is probably measured more accurately.

Some quantification here

 

[Ophiolite]

You are all missing the obvious solution. Log on to Physics Forums and check the date.

 

[Vreejack]

Check the positions of the stars. Their proper motions are known and can be projected into the future with a great deal of reliability. The long hand of the galactic clock turns very slowly.

If the stars have not moved then check the inclination of the Earth's axis, which varies in a predictable fashion. Likewise with the orbital details of the planets. I think that will work well over a 10k-100k period.

In 200 million years the ocean basins will have changed significantly and the earth/moon tidal coupling will be different...lower, I believe. You cannot use a constant recession rate.

 

[IsometricPion]

Or is this ratio method you speak of using uranium isotopes in the Earth's crust that have always been there ?

Uranium-238 - Lead-206 dating (using ratios of Lead-206 to Lead-207 to control for possible chemical effects on the system) can be used to measure long time periods with crustal rocks (that is, any rocks with a low enough initial uranium to lead ratio that haven't undergone significant reprocessing over the desired time period).

Pulsar rotation rates (Hz) and their rates of change (Hz/sec.) are very well known, and would probably be reliable over geological timescales (neglecting unforeseen circumstances). Additionally, given the distances to a large number of these pulsars (which would be recognizable by their spin rates and masses) and a computer that could simulate the orbital motions in the galaxy, one could determine a rough estimate of the time period (~10^6-10^7 years during the next few hundred million to several billion years). Over cosmological timescales (10's of billions of years to the limits of the precision of the temperature measuring device (perhaps a google years)), the temperature of the cosmic microwave background could be used (with ever decreasing precision as to the time period). The rate of increase in the Sun's luminosity might be stable enough to give a rough estimate. Planetary positions are accurately predicted for the next few thousand years. Stellar position calculations (not including changes in the rotation rate of the earth) are probably accurate over a few hundred thousand years (even if galactic orbits are not well known). The inspiral rates of various pulsar binary systems are also well-known and probably very stable (at least as stable as the rotation rates).

It turns out that pulsar rotation rates are stable to about 1 in 10^10 for averaging times of a few hours (so the time period could be estimated over the course of less than 24 hours) (from Arxiv: 1004.0115v3). So, that would mean 6 months to a year over the course of the rest of the projected main sequence lifetime of the Sun.

 

[Vreejack]

The "Long Now" clock is designed to work for 10k years, you could consult that to find the exact date for the next ten millenium, but I wonder if there is a natural clock precise enough to provide an exact date on geologic time scales.

Not that anyone would actually need to now the exact date 1 million years from now: the calendar would have to be modified a bit to make any sense, but if, after waking up from some magical million-year sleep, would it be possible to determine how long you had been out to the nearest day, hour, or some other specified level of precision?

 

[DaveC426913]

I think the movement of the stars would be the measurement least prone to errors.

Virtually all other tests mentioned here either have factors that might change in unpredictable ways in the future (such as the shape of oceans or the Earth-Moon distance), or have short-term usefulness (tilting of Earth's axis repeats every 26K years), or require a wide sample (radioactive isotopes of Earth).

Not only would a single star (in theory) give us a measurement, but each addtional star would only serve to corrobarate and refine the measurement. They are readily available for the observation (in principle, one needs no equipment whatsoever, one could use naked eye sighting) and their patterns never repeat.

 

[Andre]

...(tilting of Earth's axis repeats every 26K years), ''.

'

Just to make sure, the tilt variation cycle of the Earth axis is 41K years. It's the precession cycle that takes 26K years, causing the north position in the celestial sphere to change constantly, but that is not interesting on this time scale. Actually these periods also change due to the dynamic changing of all forces acting on the earth.

 

[MrNagy88]

Measure the age of the Earth -- using Uranium isotope ratios or something (or you could just read it on Wikipedia if they still have scientists and wikipedia then) -- and see how much it differs from the 4.5 billion years we have today. That would be good for really long leaps forward (more than 100 million years), but the resolution is not very fine so not good for less than that.

How about looking at the continents... how much have they moved? What was the spreading rate before you left? Of course, ideas like that (and the moon idea) are probably not very reliable over long distances of time, because the rate of drift is likely to change with time -- perhaps we would need to factor in the second order term of acceleration to improve our estimates...?

Does that take into account the decreasing effects of tidal forces as the moon's distance increases?

 

[DaveC426913]

Does that take into account the decreasing effects of tidal forces as the moon's distance increases?

This is why I don't think it's as reliable. We might miss something in our calcs of the Moon's distance, or it might get changed by an unprecedented event.

No danger of this with a star's movement - let alone the corrobaration from myriad stars.