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View Full Version : Was the movie "Close Encounters of the Third Kind" right about timedilation?



WaxRubiks
2008-Oct-21, 12:57 PM
Sorry to start another thread about time dilation in the same day, but I wanted to ask something that has been bothering me for years.

In the 70s movie "Close encounters of the Third Kind", the alien ship lands near the end of the film, and out come people who were abducted, by the aliens, back in the 1940s, and they hadn't aged much.

The idea being that the ship they had been on(perhaps to the aliens home planet light years away) had been traveling at relativistic speeds for most of the time since the 1940s, and so time dilation had meant that they hadn't experienced the same amount of time.

What I don't understand is, if the ship had been moving away from the Earth at velocity v(v being a bit less than the speed of light), the the Earth was also moving, relatively, at v away from the ship, so time would appear as slow on the ship, as viewed by people on Earth, and time on the Earth would have been viewed as slow by the people on the ship.

As the ship headed back to Earth at v, wouldn't time on the ship appear as fast by the people on Earth and the time on Earth would be viewed as fast by the people on the ship, due to blue shift.....

So if the ship left in 1945 then it could have returned in the 1940s even if it had traveled to the other side of the galaxy and back(assuming that v was very close to the speed of light).

I don't know; it's a bit confusing...

There is the time delay with the rover on mars; so I don't know.

So why would the time dilation only apply to the space ship and not to the Earth; if that was the standard answer?


I was going to post this in Q&A, but I thought it might be a bit ATM, and I'm running low on Q&A ATM tokens :D

So I'll add that, maybe time delay only applies to light signals, and not physical objects; which would be really ironic; AND would explain why, if the Universe were teeming with life, there are no radio signals-because information is sent by close to the speed of light space vessels....

Now I'm glad I didn't post that in Q&A. :lol:

SagoSans
2008-Oct-21, 01:39 PM
I don't know; it's a bit confusing...


Maybe the Twin Paradox (http://www.physics.adelaide.edu.au/~dkoks/Faq/Relativity/SR/TwinParadox/twin_paradox.html) is confusing you. Give it a try!

WaxRubiks
2008-Oct-21, 02:52 PM
thanks Sagosans

So it is something to do with accelerating reference frames...


I wonder about the exhaust gases, or equivalent....they might seem trivial but maybe they're not.

WaxRubiks
2008-Oct-21, 02:56 PM
also I was thinking:then if it weren't for lights interaction with matter(some sort of accelerating of something; maybe electron wave functions) then light could be beamed to the other side of the Galaxy and back with no time delay. Maybe?

grant hutchison
2008-Oct-21, 03:26 PM
Time dilation makes each observer measure the other's clock as running slowly, when observers are in relative motion. So that's going to be happening whenever the spacecraft is travelling at a constant velocity, either towards or away from Earth.
In addition to that, the observer who shifts from one inertial frame to another experiences a simultaneity shift during that process: when the spacecraft turns around, it is simultaneous with a big chunk of Earth's timeline during only a small part of its own timeline. That is where the differential ageing accrues.
On top of that, and irrelevant to the actual differential ageing, are light-travel effects which produce the appearance of time running faster when observers approach each other, and the appearance of an extra slowing (over and above time dilation) when observers are moving apart.

Grant Hutchison

cjameshuff
2008-Oct-21, 03:29 PM
also I was thinking:then if it weren't for lights interaction with matter(some sort of accelerating of something; maybe electron wave functions) then light could be beamed to the other side of the Galaxy and back with no time delay. Maybe?

Afraid not. The constant "c" that is so important in Relativity is the speed of light in the absence of anything that might cause it to slow down.

trinitree88
2008-Oct-21, 03:50 PM
Sorry to start another thread about time dilation in the same day, but I wanted to ask something that has been bothering me for years.

In the 70s movie "Close encounters of the Third Kind", the alien ship lands near the end of the film, and out come people who were abducted, by the aliens, back in the 1940s, and they hadn't aged much.

The idea being that the ship they had been on(perhaps to the aliens home planet light years away) had been traveling at relativistic speeds for most of the time since the 1940s, and so time dilation had meant that they hadn't experienced the same amount of time.

What I don't understand is, if the ship had been moving away from the Earth at velocity v(v being a bit less than the speed of light), the the Earth was also moving, relatively, at v away from the ship, so time would appear as slow on the ship, as viewed by people on Earth, and time on the Earth would have been viewed as slow by the people on the ship.

As the ship headed back to Earth at v, wouldn't time on the ship appear as fast by the people on Earth and the time on Earth would be viewed as fast by the people on the ship, due to blue shift.....

So if the ship left in 1945 then it could have returned in the 1940s even if it had traveled to the other side of the galaxy and back(assuming that v was very close to the speed of light).

I don't know; it's a bit confusing...

There is the time delay with the rover on mars; so I don't know.

So why would the time dilation only apply to the space ship and not to the Earth; if that was the standard answer?


I was going to post this in Q&A, but I thought it might be a bit ATM, and I'm running low on Q&A ATM tokens :D

So I'll add that, maybe time delay only applies to light signals, and not physical objects; which would be really ironic; AND would explain why, if the Universe were teeming with life, there are no radio signals-because information is sent by close to the speed of light space vessels....

Now I'm glad I didn't post that in Q&A. :lol:


frogmarch. That's supposed to be flight 19...see:http://en.wikipedia.org/wiki/Flight_19 that disappeared. Since then I believe they found debris from the aircraft, so the mystery has lessened. pete

Abelian Grape
2008-Oct-21, 04:49 PM
frogmarch. That's supposed to be flight 19...see:http://en.wikipedia.org/wiki/Flight_19 that disappeared. Since then I believe they found debris from the aircraft, so the mystery has lessened. pete
Not much of a mystery, ever, except for the woo-woo crowd. The causes of the loss of Flight 19 were known right from the start. The Wikipedia article referenced above covers the topic rather thoroughly. Basically, the senior officer on the flight, a Lt Taylor -- who had arrived late for the exercise and tried to beg off -- "became confused." It has always sounded to me like his confusion started before they took off.

Later on during the flight, Taylor became convinced (deluded) that he was over the Florida Keys, near which (Miami) he had recently been stationed. SOP when lost over the Keys was to head NE. That would usually get you over land and near Miami. Unfortunately, when you head NE from the Bermuda area, your next stop is in Europe, and their planes didn't carry enough fuel to get there. The last transmission heard from the flight was an order to fly east -- i.e., out over the Atlantic -- in what at the time was (contrary to the usual Bermuda Triangle blather) high winds and rough seas.

The planes they were flying floated about like a brick doesn't. Anyone who survived a landing on the water had seconds to get out, just to be above water. The planes' crews chances of survival were just about nil.

I've seen a documentary in which an attempt was made to find the planes, using modern technology for scanning the ocean bottom, and with submersibles to investigate. They did find some planes (Flight 19 was not unique), but the IDs didn't match those they expected. AFAIK the remains of that ill-fated flight are still to be found, somewhere out there in the North Atlantic.

BTW, despite its great renown among some moviegoers, I consider Close Encounters to be one of the silliest, least enjoyable films I've had occasion to suffer through. Some great tuba playing notwithstanding.

tdvance
2008-Oct-21, 05:12 PM
It might be because of my mathematical background, but the best explanation of the "twin paradox" I'd ever seen is in Roger Penrose's book, "The Road to Reality" that features a graph (one axis space, the other, time) with a straight line path (think, the Earth), and a path going out and coming back (think, spaceship leaving, then returning), to make a triangle with rounded corners (rounded, because acceleration was not instant). The idea is, in the Lorentzian metric (special relativity, but a reasonable approximation to GR if ship stays away from, say, black holes) it is a little "backward" from distances as we normally think of them (and as drawn in the diagram)--instead of "shortest distance between two points is a straight line", it is "the largest amount of time passing between two space-time events is along a straight line (geodesic)". Thus, you see, by analogy in the diagram, that because the trip through spacetime looks longer for the ship than for the straight-line Earth (close enough--given that it doesn't revolve around the sun at relativistic speeds, etc.), the amount of time passing must be less. It is the one that accelerates, decelerates, turns around, accelerates, then decelerates that makes the non-straight path. The Earth makes the straight path.

To think of time dilation purely in terms of speed of X relative to Y can give you the wrong answer. If there's never an acceleration, turn, deceleration, etc., it works fine. Otherwise, better to use an analogy diagram like Penrose's to see what is really going on.

grant hutchison
2008-Oct-21, 05:29 PM
... a graph (one axis space, the other, time) with a straight line path (think, the Earth), and a path going out and coming back (think, spaceship leaving, then returning), to make a triangle with rounded corners (rounded, because acceleration was not instant).I've used something similar when discussing the twin paradox, though with sharp corners (instantaneous acceleration) because of a lack of graphing skills.:sad:
Here (http://www.ghutchison.pwp.blueyonder.co.uk/relativity/simultaneity3.jpg) it is. Earth's worldline goes vertically, spaceship goes out and back. Equal intervals of proper time on both worldlines are marked off with red dots. Blue horizontal lines connect events that are simultaneous in Earth's frame; green slanting lines mark simultaneity in the ship's two separate frames.
By following the simultaneity lines, we can see how each observer measures the other's clock running slow, and we can also see the jump in (green) simultaneity that occurs when the ship turns around. That's where the asymmetry in ageing occurs.

Grant Hutchison

Jim
2008-Oct-21, 07:04 PM
I was going to post this in Q&A, but I thought it might be a bit ATM, and I'm running low on Q&A ATM tokens.

I don't think this thread requires a token. It seems best suited to Q&A.

Well, as long as no one claims Close Encounters was a documentary.

pzkpfw
2008-Oct-21, 08:10 PM
Just to be clear, could I ask for confirmation of an aspect?

I've read (and thought I understood it at the time) that it's not the acceleration, per se, that causes the "imbalance" in the "Twins Paradox", but the changing intertial frames of (say) the spaceship. After all, the "sharp corners" in Grants' diagram don't make it wrong, do they?

One of the pages (yes, internet) I read on it invoked already-moving spaceships in the "twins paradox", one moving "away" from Earth and one moving "towards" Earth. This way, neither accelerates during the experiment. (Which did require a way to synchronise watches as spaceships pass each other and Earth).

(This may seem like a daft distinction, because it's the acceleration that causes that shift in intertial frame...)


Further, does this means it's more about which of the Twins is simply following his/her Geodesic most closely?

grant hutchison
2008-Oct-21, 08:32 PM
Just to be clear, could I ask for confirmation of an aspect?

I've read (and thought I understood it at the time) that it's not the acceleration, per se, that causes the "imbalance" in the "Twins Paradox", but the changing intertial frames of (say) the spaceship.That's right.
One can frame a version of the "twin paradox" in which no-one accelerates: a clock setting is just handed off between two spacecraft that have constant velocities, one heading away from the Earth and one returning. Under those circumstances, the sharp corner at the right of my diagram is just the point at which the clock setting is passed between two spaceships. The second clock has been synchronized with the first clock, which has previously been synchronized with an Earth clock, but the second clock arrives at Earth showing a shorter elapsed time than the Earth clock has measured. The resolution to this apparent paradox lies in the simultaneity shift that's associated with the change in inertial frames.

Grant Hutchison

JustAFriend
2008-Oct-21, 10:13 PM
Just to throw some mess into the mix....

The Flight19 boys disappeard in 1945 so if they instantaneously accelerated to
light-speed out and then returned they could have only gone 16 light-years.
( 1977 - 1945 / 2 )

But there were many many other people that also came out of the ship with
dates on the big glass photo board right up until little Barry was snatched too.

...so the ETs had to have been zipping back and forth across the local system
stopping just long enough to snatch up a victim now and then..... strange folk indeed!!!

mugaliens
2008-Oct-21, 10:32 PM
Some great tuba playing notwithstanding.

Actually, it was the Moog synthesizer, was it not? Or did they use real tubas because the synths in those days weren't up to it?

01101001
2008-Oct-21, 11:15 PM
Actually, it was the Moog synthesizer, was it not? Or did they use real tubas because the synths in those days weren't up to it?

ARP!

Wikipedia: Phil Dodds (http://en.wikipedia.org/wiki/Phil_Dodds), synthesist.

But, I do think they used real brass in the data exchange.

Wikipedia: Tommy Johnson (http://en.wikipedia.org/wiki/Tommy_Johnson_(session_musician)), tubist

LA Times: The bass of the brass (http://articles.latimes.com/2004/jan/18/entertainment/ca-meyer18):


In another Williams score, “Close Encounters of the Third Kind,” the voice of the mother ship was played by [Jim] Self.

AGN Fuel
2008-Oct-22, 12:44 AM
Frankly, it sounded as though they were playing the synthesiser with a tuba.

thorkil2
2008-Oct-22, 06:25 AM
also I was thinking:then if it weren't for lights interaction with matter(some sort of accelerating of something; maybe electron wave functions) then light could be beamed to the other side of the Galaxy and back with no time delay. Maybe?

...with no time delay for the photon. For you, aiming the beam, it will still take a very long time to get to "the other side" but for the photon (in its frame of reference) no time at all. This was just discussed in another thread.

The symmetry of mutual observational similarity between different relativistic frames is broken when one frame has spent part of its trip in a non-inertial state (i.e., accelerating/decelerating). Hence the twin paradox is no paradox at all.