# Dilated Time: What were they smoking?

#### SexyElf

Hey all,

I am nearly finished a grade 12 physics course, and am loving it, however there is one theory from the entire course that is making me go insane. And as you may have guessed (since it is the subject) is the lovely dilated time theory (or law, or whatever you want to call it).

So, from what I've read, it can be solved through a mathematical equation that someone on a moving object, could essentially witness the birth and death of a solar system because they are moving so fast in their space shuttle? Let's look at the twin paradoxs: You leave earth at some amazing, incrediable speed. You start traveling when you are only 10, and travel across the universe. When you return, you are now 90 years old, while the earth may have passed near 400 years. (those being extreme conditions/speeds)

How exactly is this possible? You can live your entire life on a spaceship, traveling at immense speeds and return to possibly find your race extinct (I say that because at the rate our civilization is going, +400 years is probably not going to happen :P).

I have been running this through my mind. Here is how I look at it:
E = Earth, S = Spaceship, P = Planet

E ====> S ====> P
While traveling on a spaceship, from earths reference, it takes you 5 years to travel to a nearby planet.
E <==== S <==== P
While returning on a spaceship, from earths reference, it takes you another 5 years to return.
Thus, Earth has passed 10 years, and you have passed 10 years.

From your reference on the spaceship, would it not also appear to take 10 earth years for the entire journey? (365 days, 24/7, etc.)

Second, if all measurements have been on Earth for recording this data/mathemathical equations for physics over the past millenia, how is it possible for us to create a time dilated equation if it is saying something that we cannot test (ie. spaceflight time dilation)?

Can anyone explain this to me without going deep into physics termology. I mean, it is hard enough figuring this out with all the physic terms. Is it possible to define any other way? :)

Thanks for any input, hopefully this is the last hurdle I have to think about :)

#### Janus

Staff Emeritus
Gold Member
SexyElf said:
Hey all,

I am nearly finished a grade 12 physics course, and am loving it, however there is one theory from the entire course that is making me go insane. And as you may have guessed (since it is the subject) is the lovely dilated time theory (or law, or whatever you want to call it).

So, from what I've read, it can be solved through a mathematical equation that someone on a moving object, could essentially witness the birth and death of a solar system because they are moving so fast in their space shuttle? Let's look at the twin paradoxs: You leave earth at some amazing, incrediable speed. You start traveling when you are only 10, and travel across the universe. When you return, you are now 90 years old, while the earth may have passed near 400 years. (those being extreme conditions/speeds)

How exactly is this possible? You can live your entire life on a spaceship, traveling at immense speeds and return to possibly find your race extinct (I say that because at the rate our civilization is going, +400 years is probably not going to happen :P).

I have been running this through my mind. Here is how I look at it:
E = Earth, S = Spaceship, P = Planet

E ====> S ====> P
While traveling on a spaceship, from earths reference, it takes you 5 years to travel to a nearby planet.
E <==== S <==== P
While returning on a spaceship, from earths reference, it takes you another 5 years to return.
Thus, Earth has passed 10 years, and you have passed 10 years.

From your reference on the spaceship, would it not also appear to take 10 earth years for the entire journey? (365 days, 24/7, etc.)
No, because of another effect of high relative speeds; you measure anything moving relative to you as shorter in the direction of motion than they measure themselves. Thus, since both the earth and planet are moving as measured from the reference of the spaceship, the distance between them is much shorter than it is as measured from the Earth's refernce. Thus the trip takes less time for you becuase the distance traversed is shorter.
Second, if all measurements have been on Earth for recording this data/mathemathical equations for physics over the past millenia, how is it possible for us to create a time dilated equation if it is saying something that we cannot test (ie. spaceflight time dilation)?
You take two really accurate clocks, put one on a jet and fly it around the world while the other stays at the airport. when the Jet returns, you see if they read different times. This test has been done, and the clocks were found to differ by the amount predicted.

#### SexyElf

Janus said:
You take two really accurate clocks, put one on a jet and fly it around the world while the other stays at the airport. when the Jet returns, you see if they read different times. This test has been done, and the clocks were found to differ by the amount predicted.
I've heard of that, do you know of any websites or videos that may demostrate this?

Thanks btw :)

Mentor

#### Event_Horizon

Janus said:
You take two really accurate clocks, put one on a jet and fly it around the world while the other stays at the airport. when the Jet returns, you see if they read different times. This test has been done, and the clocks were found to differ by the amount predicted.
This test was actually testing gravitational time dilation.. which affects the clock more than traveling on a jet plane's speed will. Down at the surface of the earth the gravitational field is stronger than up at let's say 40000 feet. Therefore the clock up there slows because it is in a higher gravitational potential then at the surface where there is lower potential.

Why this happens I still cannot understand. I kind of understand regular time dilation due to relativistic speeds (minus the fact that biologically the clock slows as well relative to an inertial observer)

But im no physicist I just love learning the conceptuality of it...

#### jtbell

Mentor
Gravitational "time dilation" alone is not sufficient to explain the results of those experiments. You have to include the speed-related effects as well, i.e. special-relativistic time dilation. In fact, the two effects act in opposite directions! (in the case of airplanes flying close to the earth's surface.) I've forgotten which one turns out to be larger in magnitude.

Both of these effects are included in a full general-relativistic analysis.

#### Doc Al

Mentor
Hyperphysics has a good discussion (with the data) of the http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/airtim.html" [Broken].

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#### jtbell

Mentor
For a more recent (2002) study of time dilation on airplanes:

Francis et al., http://tycho.usno.navy.mil/ptti/ptti2002/paper20.pdf [Broken]

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#### Hurkyl

Staff Emeritus
Gold Member
This test was actually testing gravitational time dilation.. which affects the clock more than traveling on a jet plane's speed will. Down at the surface of the earth the gravitational field is stronger than up at let's say 40000 feet. Therefore the clock up there slows because it is in a higher gravitational potential then at the surface where there is lower potential.
Er, you have the effect backwards. If gravitational time dilation was the only factor, the clock in the jet would "run faster" than the clock on the surface.

#### Gelsamel Epsilon

So maybe some rich guys will want to live longer and therefore fly easterly around the world 24/7 so they don't age at exactly 1year/year but a bit less instead =p.

Does this also mean that people living on mountains live relatively longer/less, I suppose faster heart beat would probably skew results.

#### Office_Shredder

Staff Emeritus
Gold Member
Gelsamel Epsilon said:
So maybe some rich guys will want to live longer and therefore fly easterly around the world 24/7 so they don't age at exactly 1year/year but a bit less instead =p.

Does this also mean that people living on mountains live relatively longer/less, I suppose faster heart beat would probably skew results.
we're talking about saving nanoseconds here...

#### HallsofIvy

Independently of the clock experiments, high speed elementary particles have longer "lifetimes" than low speed particles of the same kind, indicating that time runs "slower" for them.

#### Garth

Gold Member
HallsofIvy said:
Independently of the clock experiments, high speed elementary particles have longer "lifetimes" than low speed particles of the same kind, indicating that time runs "slower" for them.
Actually, an observer's own proper time always runs at "one second per second".

The world-line observer on the aircraft, or at the bottom of a mountain, is shorter (integrated $d\tau$) than that of a stationary observer, or one at the top of a mountain.

Garth

#### Office_Shredder

Staff Emeritus
Gold Member
Garth said:
Actually, an observer's own proper time always runs at "one second per second".
That would be the point..... if the particle lasts one second, a low speed particle's second takes about a second to pass, while a high speed particle's second takes ten seconds to pass relative to us

#### Gelsamel Epsilon

Office_Shredder said:
we're talking about saving nanoseconds here...
Yeh I know that, I was being facetious.

#### yogi

Gelsamel Epsilon said:
So maybe some rich guys will want to live longer and therefore fly easterly around the world 24/7 so they don't age at exactly 1year/year but a bit less instead =p.

Does this also mean that people living on mountains live relatively longer/less, I suppose faster heart beat would probably skew results.
The aging doesn't really extend the lifetime so that traveler gets a benefit of enjoying a longer lifespan - he will eat the same number of meals, drink the same number of beers, etc - but he is able to see more of the universe because part of his lifeline is spatial and part is temporal - he might travel at o.999c and circumnavigate the entire universe - and only age 50 years - so he would have a very brief look at each object - its sort of like being in a frozen state - you may live along time - but your not getting much out of it.

F

#### Futobingoro

##### Guest
Janus said:
You take two really accurate clocks, put one on a jet and fly it around the world while the other stays at the airport. when the Jet returns, you see if they read different times. This test has been done, and the clocks were found to differ by the amount predicted.
How does the 300+ km/second galactic velocity factor into this?

One would think that, under certain conditions, the clock on the jet would 'age' faster relative to the airport clock, assuming that the jet happened to be traveling in the opposite direction of the galaxy.

A miniscule, albeit relevant, effect.

Of course the Earth's rotation, solar orbit and galactic arm rotation all play into this as well.

#### pervect

Staff Emeritus
Futobingoro said:
How does the 300+ km/second galactic velocity factor into this?
Not at all, according to relativity.

One of the main points of relativity is that "absolute velocity" is not detectable experimentally, only relative velocity can be detected.

Thus if relativity is correct, "galactic velocity" does not matter for any experiment performed entirely inside the galaxy.

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