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In the scifi tv series- Terminator the Sarah Connor chronicles, there was an episode wherein a time travelling robot lands at around the 1950's and he looks up at the night sky to confirm that he has landed on the correct date. I am not sure how this is possible as in order to detect the difference in the parallax measurements, he should have a very powerful telescope that will be too big to be fitted into his eye socket. He would also need an extraordinarily powerful instrument to determine the shift of the Polaris relative to the earth's rotational axis. Is this assumption correct or is it theoretically possible to determine the date (year at least ) within a short period of time?

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If solar system bodies are present in the sky you can use that to get a pretty good fix on date and time from their positions as they are relatively bright and change position rapidly. Then, assuming you know geographic location, the exact time is simply the right ascension of any star.

I am sure the mechanism they use does not rely on Polaris, as they might be deployed in the southern hemisphere too.

Edited by Ags
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16 hours ago, andrew s said:

You could use the precise position of the pole. Not too difficult for an AI.

Regards Andrew 

but I am assuming that one needs to track the rotation of the stars for some time to determine the earth's axis of rotation and then see how far away Polaris is from that point. This process should take at least a few minutes rather than seconds even for a powerful AI?

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Not too sure about this one but wouldn't it be possibe to "solve" based on planetary positions? I know they repeat eventually but it should pin it down to a few possible years, widely separated enough to pick the right one. Of course, had they landed in the UK there'd be little chance of a clear sky 😞

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3 hours ago, speckofdust said:

but I am assuming that one needs to track the rotation of the stars for some time to determine the earth's axis of rotation and then see how far away Polaris is from that point. This process should take at least a few minutes rather than seconds even for a powerful AI?

If the robot knows its latitude, it should be able to determine the declination of the stars by observing their altitude and azimuth. If it knows the declination of some stars, it can calculate the date using a reversed precession calculation. Provided it travels to a sufficiently distant date in the past or future. The precession circle is not a closed circle, so it should be pretty accurate.

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30 minutes ago, Waddensky said:

If the robot knows its latitude, it should be able to determine the declination of the stars by observing their altitude and azimuth. If it knows the declination of some stars, it can calculate the date using a reversed precession calculation. Provided it travels to a sufficiently distant date in the past or future. The precession circle is not a closed circle, so it should be pretty accurate.

Another approach: it performs photometry on a number of stars with precisely known periods: Algol, Delta Cephei, etc. Comparing with its in-built ephemerides, it can predict a list of possible times for each. With enough stars, only one plausible time will be present in every list.

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Having given this  some thought the simplest  idea I can come up with is to view the field of a star with high proper motion.  It current position will with a simple calculation give the date.

Regards Andrew 

Ps corrected ascoointed out by @Xilman

Edited by andrew s
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Just now, andrew s said:

Having given this  some thought the simplest  idea I can come up with is to view the field of a star with high radial velocity.  It current position will with a simple calculation give the date.

Regards Andrew 

Tangential velocity, but otherwise the approach is sound.

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On 19/12/2020 at 10:01, speckofdust said:

In the scifi tv series- Terminator the Sarah Connor chronicles, there was an episode wherein a time travelling robot lands at around the 1950's and he looks up at the night sky to confirm that he has landed on the correct date. I am not sure how this is possible as in order to detect the difference in the parallax measurements, he should have a very powerful telescope that will be too big to be fitted into his eye socket. He would also need an extraordinarily powerful instrument to determine the shift of the Polaris relative to the earth's rotational axis. Is this assumption correct or is it theoretically possible to determine the date (year at least ) within a short period of time?

Now I have to re watch my DVDs of the series ... I thought Summer Glau did a great job as a terminator, her dance background gave her a very different but effective presence. I liked her performance in the excellent  Firefly / Serenity and watched the SCC  because of it.

However, I'm slightly worried that the whole time traveling humanoid self healing robot concept gets through your suspension of disbelief with ease, with just the astronomy component a sticking point ! 😀

Heather

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1 hour ago, Tiny Clanger said:

Now I have to re watch my DVDs of the series ... I thought Summer Glau did a great job as a terminator, her dance background gave her a very different but effective presence. I liked her performance in the excellent  Firefly / Serenity and watched the SCC  because of it.

However, I'm slightly worried that the whole time traveling humanoid self healing robot concept gets through your suspension of disbelief with ease, with just the astronomy component a sticking point ! 😀

Heather

the concept of time travelling terminator is a moot point, which forms the sci-fi premise for the tv series and the movie. a bit pointless to argue with that, but we can analyse the remaining aspects which are presented as science. 

Anyway glad to see that this has generated quite a bit of discussion and I have some ideas for me to determine the exact date if I were to wake up in the middle of nowhere, although I wouldnt have the appropriate equipment for some of the methods suggested above.🤔

Edited by speckofdust
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58 minutes ago, speckofdust said:

the concept of time travelling terminator is a moot point, which forms the sci-fi premise for the tv series and the movie. a bit pointless to argue with that, but we can analyse the remaining aspects which are presented as science. 

Anyway glad to see that this has generated quite a bit of discussion and I have some ideas for me to determine the exact date if I were to wake up in the middle of nowhere, although I wouldnt have the appropriate equipment for some of the methods suggested above.🤔

(Engage Austrian accent) "I need your clothes, your boots, your motorcycle and your high end telescope set up  ... " 😀

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2 hours ago, Tiny Clanger said:

 and your high end telescope set up  ... " 😀

Which is why I suggested the photometric approach. A 8mm refractor (human eyeball size) can easily reach 10th magnitude with an accuracy of  under 50mmag in an exposure of few seconds when coupled with a detector with a 80% QE. There are a good number of EA, EB, DCEP, etc. variables brighter than tenth magnitude.

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I reckon it would be quite a big ask technologically.

Even with a system configured with all the necessary hardware, software and data, it would be quite something to dump it somewhere in time somewhere on Earth and calculate the year from one single astronomical observation.

What likely happened here is that one of the writers had hear of the concept of Precession of the Equinoxes and how that affects the positions of the stars relative to our reference systems. They took the huge leap and concluded that it would be possible to do as per the scene in the film.

Ah! But even though time machines put the traveller somewhere else in space in a lot of films, a real time traveller will already know his geographical location so the calculation just got easier! :) 

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16 hours ago, Paul M said:

Ah! But even though time machines put the traveller somewhere else in space in a lot of films, a real time traveller will already know his geographical location so the calculation just got easier! :) 

Just a thought...

If they only jump in time, would the earth not be there when you stop jumping?

And possibly for that matter, the rest of the solar system too if you jump enough...

Gordon.

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27 minutes ago, Bukko said:

Just a thought...

If they only jump in time, would the earth not be there when you stop jumping?

And possibly for that matter, the rest of the solar system too if you jump enough...

Gordon.

You aren't supposed to notice "minor" details like that!

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I don't think the time travel aspect is moot. Given the significant technology required for such then it is more than likely that the robot would be equipped with other similarly advanced technology. If they have developed the technology to time travel then it would be equally probable that they have developed sophisticated and more powerful optical devices. Perhaps then he used something  equally beyond our understanding - self contained within his eyes.  Rather than taking a cosmological fix perhaps the AI was measuring background radiation.  The first atom bomb was detonated in 1945 , first Hydrogen bomb in 1950 , each detonation leaving its own unique trace in the upper atmosphere.  Perhaps he was taking a half life sample.  He may even have just been scanning radio broadcasts.

Jim 

Edited by saac
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On 24/12/2020 at 13:30, Bukko said:

If they only jump in time, would the earth not be there when you stop jumping?

If you jumped many billions of years then perhaps the Earth wouldn't be still there at the end of your journey.

A physically fixed machine would put the traveller in the exact same spot they departed from. However the bets are off if the time machine is an old car that has to travel at some precise speed to make the time jump :)

I've spent a lot of time thinking about time travel; where would I like to go or more correctly, when?

I wouldn't want to go forward and know either my own fate or anyone else's.  I'm not interested enough in recent human history to take a look there. So my destination would be prehistoric Earth, the Jurassic period perhaps. Lush forests being grazed by Brontosaurus and Pterodactyls soaring in the sky (I don't know if they actually coexisted but you get the idea). An Earth not yet bothered by humans. How wonderful would that be? 

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2 hours ago, Paul M said:

If you jumped many billions of years then perhaps the Earth wouldn't be still there at the end of your journey.

A physically fixed machine would put the traveller in the exact same spot they departed from. However the bets are off if the time machine is an old car that has to travel at some precise speed to make the time jump :)

I've spent a lot of time thinking about time travel; where would I like to go or more correctly, when?

I wouldn't want to go forward and know either my own fate or anyone else's.  I'm not interested enough in recent human history to take a look there. So my destination would be prehistoric Earth, the Jurassic period perhaps. Lush forests being grazed by Brontosaurus and Pterodactyls soaring in the sky (I don't know if they actually coexisted but you get the idea). An Earth not yet bothered by humans. How wonderful would that be? 

Not sure Paul, might be wrong here but , the Earth moves through spacetime in a spiral as it orbits the sun , rotates on its own axis, and follows the sun's orbit around the centre of the galaxy.  I'm guessing if it were a short jump in time then then you'd end up displaced a few cm - best to do it with plenty of space around you.  If it were  a longer jump in time then you better wear a space suit - you may land off the planet :) 

Jim 

 

 

 

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Edited by saac
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10 minutes ago, saac said:

Not sure Paul, might be wrong here but

I'm sure you are right! Maybe...

I got carried away with trying to rebut the idea that a time machine also projects someone to a specific geographical location too. I've alway thought about time machines simply shorting across that helical time line. What was or would be at your destination time in the natural passage of time would still be there when you arrive at your chosen jump time. 

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