Time slowing down for someone traveling just under the speed of light

In summary, the concept of time dilation due to relative velocity is mutual between inertial frames, with each frame observing the other's clock ticking more slowly. However, in cases of differential aging, such as a spaceship traveling in a circle, the situation is not symmetric and one frame will age less than the other. The twin paradox is a useful analogy for understanding this concept, and resources such as the Doppler Shift Analysis and the Spacetime Diagram Analysis can help visualize the phenomenon.
  • #1
mycotheology
89
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Lets say ship 1 is traveling just under the speed of light so time slows down for the crew and the age less quickly than the stationary crew in ship 2. Relative to the crew in ship 1, the crew of ship 2 are traveling at just under the speed of light, so time moves slower for them and they should be the ones aging more slowly. Which is it?
 
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  • #2


mycotheology said:
Which is it?

It's both. Time and time dilation are relative, not absolute.
 
  • #3


mycotheology said:
Which is it?
The one that fired its engines, which you didn't specify.
 
  • #4


russ_watters said:
The one that fired its engines, which you didn't specify.

What if they both fired their engines. Anyway, it doesn't matter unless they get back together. There is no sense in which you can pick which one is 'really' slower if they just travel away from each other, possibly exchanging signals.
 
  • #5


mycotheology said:
Lets say ship 1 is traveling just under the speed of light so time slows down for the crew and the age less quickly than the stationary crew in ship 2. Relative to the crew in ship 1, the crew of ship 2 are traveling at just under the speed of light, so time moves slower for them and they should be the ones aging more slowly. Which is it?
Time dilation between inertial frames is mutual - according to each reference system it is the clock at rest in the other system that is ticking more slowly. This disagreement is due to disagreement about who is "in rest" and related things such as distant simultaneity.
See for example the elaborations here: http://en.wikipedia.org/wiki/Time_d...relative_velocity_symmetric_between_observers
 
  • #6
PAllen said:
What if they both fired their engines. Anyway, it doesn't matter unless they get back together. There is no sense in which you can pick which one is 'really' slower if they just travel away from each other, possibly exchanging signals.
Agreed.
 
  • #7


harrylin said:
Time dilation between inertial frames is mutual - according to each reference system it is the clock at rest in the other system that is ticking more slowly. This disagreement is due to disagreement about who is "in rest" and related things such as distant simultaneity.
See for example the elaborations here: http://en.wikipedia.org/wiki/Time_d...relative_velocity_symmetric_between_observers

I read that if a spaceship is traveling at a really high speed, let's say just under lightspeed, that the crew will age more slowly than us earthlings because time slows down when they are traveling at such a high speed. What doesn't make sense to me is that relative to the spaceships crew, its the Earth that is traveling at an extremely high speed so its the earthlings clocks that slow down. Let's say the spaceship travels around in a circle and returns to Earth 15 years later. Will the earthlings have aged more than the crew of the spaceship? From the spaceships perspective, it should be the earthlings that aged slower.

russ_watters said:
The one that fired its engines, which you didn't specify.
Isn't it irrelevant who fired the engine? I meant to imply that spaceship 1 fired the engine and took off at just under light speed relative to spaceship 2. The crew of spaceship 2 will observe that spaceship 1s clocks have slowed and the length of the spaceship has contracted. Whats confusing me is that relative to the ship 1 (the fast moving ship), ship 2 is the one that's traveling at just under lightspeed. So does time dilation occur for both ship 1 and ship 2? I'm a full on visual thinker so this is a real mind boggler for me. Trying to come up with a way to visualise this concept.
 
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  • #8


mycotheology said:
I read that if a spaceship is traveling at a really high speed, let's say just under lightspeed, that the crew will age more slowly than us earthlings because time slows down when they are traveling at such a high speed. What doesn't make sense to me is that relative to the spaceships crew, its the Earth that is traveling at an extremely high speed so its the earthlings clocks that slow down. Let's say the spaceship travels around in a circle and returns to Earth 15 years later. Will the earthlings have aged more than the crew of the spaceship? From the spaceships perspective, it should be the earthlings that aged slower.

No, if the spaceship travels in a circle the situation is not symmetric. This becomes a case of differential aging (not symmetric) rather than time dilation. The spaceship traveling in a circle is not inertial, and cannot pretend they are at rest in an inertial frame and use the normal SR formulas. The spaceship traveling in a circle will age less.
 
  • #9


mycotheology said:
I'm a full on visual thinker so this is a real mind boggler for me. Trying to come up with a way to visualise this concept.

You might try the Usenet Physics FAQ entry on the twin paradox:

http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html

In particular, the Doppler Shift Analysis and the Spacetime Diagram Analysis.

The Doppler Shift Analysis focuses on what each twin actually sees, in the sense of the actual light signals each twin receives from the other; this might help in visualizing since it removes all the abstractions about "time dilation" and just focuses on the actual observations.

The Spacetime Diagram Analysis gives a sort of "God's eye view" of what is happening and how it all fits together globally.
 
  • #10
mycotheology said:
Isn't it irrelevant who fired the engine?
That would mean that nothing happened to the rocket that fired its engine, but the other rocket that did nothing accelerated.
 
  • #11


PeterDonis said:
You might try the Usenet Physics FAQ entry on the twin paradox:

http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html

In particular, the Doppler Shift Analysis and the Spacetime Diagram Analysis.

The Doppler Shift Analysis focuses on what each twin actually sees, in the sense of the actual light signals each twin receives from the other; this might help in visualizing since it removes all the abstractions about "time dilation" and just focuses on the actual observations.

The Spacetime Diagram Analysis gives a sort of "God's eye view" of what is happening and how it all fits together globally.

Ah, so its called the twin paradox. Thanks a lot. Hopefully those FAQs will resolve it for me. The wiki page looks good too.
 
  • #12


mycotheology said:
Ah, so its called the twin paradox. Thanks a lot. Hopefully those FAQs will resolve it for me. The wiki page looks good too.

Be careful. There are two deceptively similar but interestingly different paradoxes.

1) The one your raised in your first post: When they're moving relative to one another, which one is "really" slow? The answer is "neither - they both see time passing more slowly for the other and there is no contradiction because of relativity of simultaneity".

2) The twin paradox: If they start out in the same place at the same time with the same age, travel for a while, then rejoin at a later time (which means that one of them has necessarily accelerated or free-fallen through a fairly exciting gravitational field) so that they can directly compare their age, which one is younger? The answer here is that one of them will be unambiguously younger.
 
  • #13


mycotheology said:
Let's say the spaceship travels around in a circle and returns to Earth 15 years later.

By whose clock(s)? Theirs, Earth's, or yours?
 
  • #14


See Misner, Charles W.; Thorne, Kip S.; Wheeler, John Archibald (1973), Gravitation, San Francisco: W. H. Freeman, ISBN 978-0-7167-0344-0.
 

1. What is the theory behind time slowing down for someone traveling just under the speed of light?

The theory behind time dilation is a fundamental concept in the theory of relativity. It states that as an object's velocity increases, time slows down for that object relative to a stationary observer. This is because the faster an object moves, the more energy it has, and this energy can distort the fabric of space-time, affecting the measurement of time.

2. How does the speed of light relate to time slowing down?

The speed of light (299,792,458 meters per second) is considered a constant in the universe. According to the theory of relativity, nothing can travel faster than the speed of light. As an object approaches the speed of light, time slows down for that object relative to a stationary observer. At the speed of light, time would theoretically stop completely for that object.

3. Can we observe time slowing down for someone traveling at the speed of light?

No, we cannot observe time slowing down for someone traveling at the speed of light because it is impossible for any object with mass to travel at the speed of light. Additionally, the effects of time dilation are only significant at extremely high speeds, such as a significant fraction of the speed of light. At everyday speeds, the difference in time is negligible.

4. How does time dilation impact space travel?

Time dilation has significant implications for space travel. As a spacecraft approaches the speed of light, time will slow down for the astronauts on board relative to people on Earth. This means that astronauts may experience a shorter passage of time during their journey, while those on Earth will experience a much longer passage of time. This effect must be taken into account for accurate navigation and communication during space travel.

5. Is time dilation only applicable to objects traveling at high speeds?

No, time dilation can also occur in other scenarios, such as in strong gravitational fields. The closer an object is to a massive object like a black hole, the stronger the gravitational pull, and the slower time will pass for that object relative to a distant observer. This phenomenon is known as gravitational time dilation and has been observed through experiments and astronomical observations.

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