| From: Brendan | 3/02/99
21:33:10 |
| Subject: Time dilation | post id:
171 |
| Can someone explain how time
dilation operates? I understand that it's a theoretical possibility
arising out of relativity theory, and describes how a physical body,
travelling at light speed (if that were possible) could "travel" through
time through the occurance of "dilation" - but I still haven't gotten my
head around the precise workings out. Also, I'd like to know more about the relationship between relativity theory and the Uncertainty Principle and quantum mechanics. Did these latter two arise out of relativity theory, or were they developed seperately? | |
| From: Evan | 3/02/99
22:12:12 |
| Subject: re: Time dilation | post id:
179 |
| Relativity says that as an object
appraoches the speed of light, time for an observer on the object slows
down. That is if you took a ship to the stars, at the speed of light, to a
location 25 lights years away, turned around and came back at the speed of
light another 25 light years to the Earth, a person aboard such a ship
would have aged 50 years. But the Earth they returned to would have aged
some 50 thousand years. If you could talk via a radio to someone abord a
ship approaching the speed of light, moving away from the Earth, they
would appear to be talking more slowly and deeply, while to them, we on
the earth would appear to be talking more rapidly and at a higher pitch.
This is because for every hour that passes on the Earth, only a second may
have passed on the ship. If you've heard a train pass through a station,
perhaps sounding it's horn, it raises in pitch until it passes you, then
it starts to drop in pitch, as it moves away, it called the Doppler
effect. | |
| From: Evan | 3/02/99
22:12:43 |
| Subject: re: Time dilation | post id:
180 |
| Relativity says that as an object
appraoches the speed of light, time for an observer on the object slows
down. That is if you took a ship to the stars, at the speed of light, to a
location 25 lights years away, turned around and came back at the speed of
light another 25 light years to the Earth, a person aboard such a ship
would have aged 50 years. But the Earth they returned to would have aged
some 50 thousand years. If you could talk via a radio to someone abord a
ship approaching the speed of light, moving away from the Earth, they
would appear to be talking more slowly and deeply, while to them, we on
the earth would appear to be talking more rapidly and at a higher pitch.
This is because for every hour that passes on the Earth, only a second may
have passed on the ship. If you've heard a train pass through a station,
perhaps sounding it's horn, it raises in pitch until it passes you, then
it starts to drop in pitch, as it moves away, it called the Doppler
effect. | |
| From: Des | 3/02/99
23:07:15 |
| Subject: re: Time dilation | post id:
182 |
| The drawcard with the speed of
light discussions is of course people wish to travel back in time and
place a bet on the last Melbourne Cup (or some other self beneficial
action). Can you then (excuse my crude extrapolation of the time dilation
theory) travel faster than the speed of light and turn back the clock? I
seem to remember that in order to achieve light speed one needs to have no
mass, any theories on how to get less than zero mass?
antimatter? | |
| From: Bill Gates | 4/02/99
10:00:14 |
| Subject: re: Time dilation | post id:
198 |
| Accelerating a vehicle to the
speed of light! Relativity causing the Doppler effect! Einstien must be turning in his grave! | |
| From: steve | 4/02/99
10:17:30 |
| Subject: re: Time dilation | post id:
205 |
| As far as I understand it (and
that is by no means extensive) the two theories (Relativity &
Uncertainty) were developed separately - the first by Einstein, the second
by Heisenberg, Bohr etc al. The connection between Relativity and Quantum Theory (of which Uncertainty is a component) is that inside the nucleus of an atom particles travel around at extraordinary high speeds. Because of this, Relativity plays a part in the calculations of mass, energy etc and in interpretation of experimental results. The thing to keep in mind when thinking about sub-atomic physics is that nothing is certain. Behaviour is described using probabilities rather than concrete causal explanations. For example, you cannot say that when a positron collides with a neutron at speed x, then y will happen. Y will happen with probability z, but a will happen with probability p etc. | |
| From: James Richmond | 4/02/99
11:42:14 |
| Subject: re: Time dilation | post id:
252 |
| Time dilation is an effect which
can be caused by relative motion or variation in the gravitational
field. Relative motion. Consider a person in a spaceship travelling at close to the speed of light, and a person on Earth watching the spaceship speed past. The first point to make is that neither person will notice anything unusual about the rate at which their subjective time flows. However, if the Earth observer has a powerful telescope and can see a clock in the spaceship, it will appear to be running slowly with respect to Earth clocks. The situation works in reverse, too: the spaceship person will see Earth clocks as running slower than spaceship clocks. The faster the relative motion, the larger the time dilation effect. If the spaceship could reach the speed of light (which is impossible for other reasons) then each observer would see the other's clocks as stopped. This effect has nothing to do with the Doppler effect, and the above explanation assumes that both observers correct for the time it takes light to travel between them. Another effect which goes hand in hand with time dilation due to relative motion is length contraction, by which moving objects shrink in the direction of motion, as seen by a "stationary" observer. Gravitational variation. Gravitational time dilation is an effect due to curved spacetime. Clocks higher up in a gravitational field are observed to run faster than clocks lower down. Both types of time dilation are not just theoretical possibilities. They have been confirmed over and over again in experiments. | |
| From: Jeremy | 4/02/99
12:10:28 |
| Subject: re: Time dilation | post id:
274 |
| Steve's summary is pretty good.
In fact all objects have a wave-function, and all moving objects are
subject to relativistic effects. It's just that as these objects become
slower and more macroscopic, the effects rapidly become negligible. In
other words, you could use relativistic equations to describe the motion
of the planets, but the difference against the result of using Newton's
would be imperceptible. (Notwithstanding Mercury in our own solar system
for example where the gravitational effect of the sun on the tiny planet
becomes measurable) | |
| From: Chris (Avatar) | 4/02/99
13:20:40 |
| Subject: re: Time dilation | post id:
300 |
| Time
Dilation …is not a "theoretical possibility", it is a real effect. Time dilation is a consequence of the postulates of Special Relativity. It works like this: Consider a single light photon bouncing elastically between two parallel mirrors. If you are in the same reference frame as the photon, you see it bounce vertically up and down. However if the frame with the two mirrors is moving past you at a speed v, then you see it move forward as it bounces In other words the path of the photon is now zig-zagged, as the two mirrors move to the right. Ok, to the stationary observer, the path length of the photon appears to have increased. If the photon was a ball, then the apparent speed of the ball to the stationary observer would be different which would account for the different path length and times - however special relativity tells us that all observers will observe the same speed of light, regardless of relative motion. What this means is that we must account for the discrepancy in the path and time length by adjusting our "common sense" notions of absolute space and time. This is done by applying a Lorentz transformation (a mathematical operation) to the observations made by the "stationary" observer. The consequence is that if I imagine a frame moving past me at velocity v, then I will observe a clock in that moving frame to run slow (time dilation). This is simply because observations of time and space depend on the observers motion with respect to the target. In the frame of the clock, it will observe time to run normally. Importantly, time dilation occurs at all velocities. In everyday velocities the effect is not noticeable, as velocities approach the speed of light, the effect becomes more noticeable. Hope this helps! Chris | |