# What happens after you travel at a relativistic speed

• gsingh2011
In summary: Maybe I misunderstood your question. See the first paragraph in "Time dilation and space flight" in the "Time dilation" Wikipedia entry. It describes the effect of a spaceship traveling close to the speed of light and the differences in time that are experienced by the people on the spaceship vs the people on Earth. One of the sentences states "the ship's clock (and according to relativity, any human traveling with it) shows less elapsed time than the clocks of observers on Earth"...which means that the clocks on Earth are running faster than the clocks on the spaceship.

#### gsingh2011

If a spaceship is moving at a relativistic speed past the earth, the people on Earth would believe that the time in the spaceship was moving slower. The people on the spaceship would believe the time on the Earth was moving slower. So what happens when the spaceship stops? Do both times revert back to normal? Because if the times just go back to the same speed, then the people on Earth would still be seeing the people in the spaceship only in the past... and that doesn't make sense. So what actually happens?

Okay, you have two frames of reference...one in which a spaceship is traveling at relativistic speed and one which, for arguments sake, we'll consider to be stationary.

As the spaceship decelerates, the time dilation effect becomes less pronounced until the spaceship is stationary...at which time the two frames of reference are temporally equivalent. The end result is that the people on the spaceship have effectively traveled into the future relative to the people in the stationary frame (meaning that during the spaceship's travels, a greater amount of time has elapsed for the people in the stationary frame of reference). With the spaceship stationary, both sets of observers now view each other in the same frame of reference...there is no "seeing the people in the spaceship only in the past".

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At high velocities time and position are not orthogonal as they are approximately at low velocities. It is no longer enough just to talk about an objects time you must also consider its place (position).

Temporal said:
Okay, you have two frames of reference...one in which a spaceship is traveling at relativistic speed and one which, for arguments sake, we'll consider to be stationary.

As the spaceship decelerates, the time dilation effect becomes less pronounced until the spaceship is stationary...at which time the two frames of reference are temporally equivalent. The end result is that the people on the spaceship have effectively traveled into the future relative to the people in the stationary frame (meaning that during the spaceship's travels, a greater amount of time has elapsed for the people in the stationary frame of reference). With the spaceship stationary, both sets of observers now view each other in the same frame of reference...there is no "seeing the people in the spaceship only in the past".

I'm pretty sure that each reference frame would view the other as having a slower time.

At high velocities time and position are not orthogonal as they are approximately at low velocities. It is no longer enough just to talk about an objects time you must also consider its place (position).

Ok, let us consider position along with time. How does that explain what happens when the spaceship stops?

What happens when the spaceship stops? You ask. Nothing happens. As the spaceship passes close to Earth at high speed both observers have approximately the same space-time position. After the ship has moved away for a long time the ship and the Earth observer have different space-time positions, dS=x. If the ship stops quickly then the difference in space-time positions is still approximately dS=x. Nothing happens. Both will observe the others clock as progressing at the same rate as their own clock (after stopping). Before stopping both observe the other's clock as progressing slowly relative to their own clock.

edpell said:
What happens when the spaceship stops? You ask. Nothing happens. As the spaceship passes close to Earth at high speed both observers have approximately the same space-time position. After the ship has moved away for a long time the ship and the Earth observer have different space-time positions, dS=x. If the ship stops quickly then the difference in space-time positions is still approximately dS=x. Nothing happens. Both will observe the others clock as progressing at the same rate as their own clock (after stopping). Before stopping both observe the other's clock as progressing slowly relative to their own clock.

Ok, so the spacetime positions are the same. How is it possible to view someone else's time as slower and still have both be the same spacetime?

gsingh2011 said:
I'm pretty sure that each reference frame would view the other as having a slower time.

Maybe I misunderstood your question. See the first paragraph in "Time dilation and space flight" in the "Time dilation" Wikipedia entry. It describes the effect of a spaceship traveling close to the speed of light and the differences in time that are experienced by the people on the spaceship vs the people on Earth. One of the sentences states "the ship's clock (and according to relativity, any human traveling with it) shows less elapsed time than the clocks of observers on Earth"...which means that the clocks on Earth are running faster than the clocks on the spaceship.

gsingh2011 said:
How is it possible to view someone else's time as slower and still have both be the same spacetime?

I'm not sure what you mean by both being the same spacetime. The spaceship traveling close to light speed will be in one frame of reference and Earth will be in another. Although they both physically exist in the same spacetime, the spaceship is encountering greater time dilation effects due to its speed and therefore its frame of reference has changed from that of Earth's. When the spaceship comes to a stop, the spaceship is now in the same frame of reference as Earth (very oversimplified because I'm discounting all other movement as well as the differences in spacetime distortion just due to the mass of the two objects).

Temporal said:
Maybe I misunderstood your question. See the first paragraph in "Time dilation and space flight" in the "Time dilation" Wikipedia entry. It describes the effect of a spaceship traveling close to the speed of light and the differences in time that are experienced by the people on the spaceship vs the people on Earth. One of the sentences states "the ship's clock (and according to relativity, any human traveling with it) shows less elapsed time than the clocks of observers on Earth"...which means that the clocks on Earth are running faster than the clocks on the spaceship.

Well, the Earth clocks are running faster according to people on Earth. But the people on the spaceship see the Earth go by at a constant velocity and therefore, the same time dilation phenomena that the people on Earth see when watching the ship occurs when the people on the ship are watching the earth. I asked many questions about this long ago and I'm pretty sure that that is the general consensus regarding this topic. Can any other members confirm this for me?

I'm not sure what you mean by both being the same spacetime.

Well, I meant the same position in spacetime. I was simply asking edpell how the spacetime positions could be the same when (relative to another) the times were different. You (Temporal) seem to have a small misunderstanding of how time dilation works, so I would look that up before attempting to answer this. (Unless I'm wrong about the whole dilation thing, that's always a possibility :) )

gsingh2011 said:
Well, the Earth clocks are running faster according to people on Earth. But the people on the spaceship see the Earth go by at a constant velocity and therefore, the same time dilation phenomena that the people on Earth see when watching the ship occurs when the people on the ship are watching the earth. I asked many questions about this long ago and I'm pretty sure that that is the general consensus regarding this topic. Can any other members confirm this for me?

As I thought...I misunderstood your scenario. The observers in the spaceship can be considered as motionless in their frame of reference as they see the Earth go by which explains why the observers on the spaceship would see the Earth clock as moving more slowly. Thanks for the clarification.

gsingh2011 said:
Well, I meant the same position in spacetime. I was simply asking edpell how the spacetime positions could be the same when (relative to another) the times were different. You (Temporal) seem to have a small misunderstanding of how time dilation works, so I would look that up before attempting to answer this. (Unless I'm wrong about the whole dilation thing, that's always a possibility :) )

Please point out what misconceptions you think I may have concerning time dilation so I can learn from this discussion.

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gsingh2011 said:
Ok, so the spacetime positions are the same. How is it possible to view someone else's time as slower and still have both be the same spacetime?

What you're describing is just Differential Aging. The leg of the journey, or the fact that the ship stops doesn't matter, as edpell has already said. Once the ship stops, observers on Earth and the ship could agree on a clock's tick rate.

gsingh2011 said:
So what happens when the spaceship stops? Do both times revert back to normal?
Yes.
gsingh2011 said:
Because if the times just go back to the same speed, then the people on Earth would still be seeing the people in the spaceship only in the past
No, not in the past. At least, not per se. During their travel in the spaceship they will not have experienced as much time passing as those on Earth. But it doesn't mean they're in the past; it means they're younger.

DaveC426913 said:
Yes.

No, not in the past. At least, not per se. During their travel in the spaceship they will not have experienced as much time passing as those on Earth. But it doesn't mean they're in the past; it means they're younger.

It's also good to point out that time was never "ABnormal"! All of this does make sense in the context of a constant "c", and presumably the ship must go through a braking period to come to a stop... so time is never jumping around, or "snapping back", because it was never deformed to begin with, anymore than spacetime is ALWAYS deformed by energy/momentum.

When the spaceship stops, 'Earth' and 'Ship' will not agree on the total amount of time passed subjectively, but their "tick rates" will be similar again. If we ignore that, this doesn't make sense as a Relativistic effect, and it seems like some kind of magical "time jump". "What happens after you travel at a relativistic speed?"... the same thing that happened before, accounting for Time Dilation/Differential Aging.

The issue is the desire for people to hang on to absolute notions in a relative world.

Thanks for all of your posts. I still do not understand completely, but your information helps me narrow down my question. So, now I understand that when the spaceship stops, clock's on both the Earth and the spaceship will not agree. The question is, how is the amount of time passed on the spaceship and the Earth the same? Or is it?

gsingh2011 said:
Thanks for all of your posts. I still do not understand completely, but your information helps me narrow down my question. So, now I understand that when the spaceship stops, clock's on both the Earth and the spaceship will not agree. The question is, how is the amount of time passed on the spaceship and the Earth the same? Or is it?

It is different, and both Earth (A) and spaceship (B) MUST agree on that at the end of the journey. That's why we have the bother of Time Dilation and Differential Aging in the first place. We all have to agree on the laws of physics at the end of the day. That's why a round trip to near lightspeed wouldn't end in a happy homecoming. Your descendants would be REALLY dead and gone (depending on trip velocity and duration of course), and everyone would agree. It's that last concept, that is RELATIVE. The subjective experience is relative, but the absolute result is not. The velocity of light in a given medium is absolute, and time and space and our subjective experiences are defined by that.

You've really learned a lot in a short period in this thread you know... restores some nonexistent faith on my part.

gsingh2011 said:
Thanks for all of your posts. I still do not understand completely, but your information helps me narrow down my question. So, now I understand that when the spaceship stops, clock's on both the Earth and the spaceship will not agree. The question is, how is the amount of time passed on the spaceship and the Earth the same? Or is it?

## 1. What is the theory of relativity?

The theory of relativity is a fundamental concept in physics that explains how time and space are perceived differently depending on the observer's relative motion. It is divided into two parts: special relativity, which deals with objects moving at constant speeds, and general relativity, which includes gravity and acceleration.

## 2. How does traveling at a relativistic speed affect time?

According to special relativity, time slows down for objects moving at high speeds. This means that if you were traveling at a relativistic speed, time would pass slower for you compared to someone who is stationary. This effect, known as time dilation, becomes more significant as the speed approaches the speed of light.

## 3. Can you travel faster than the speed of light?

According to the theory of relativity, it is impossible for any object with mass to travel at the speed of light. As an object approaches the speed of light, its mass and energy increase infinitely, making it impossible to reach or exceed this speed. This is why the speed of light is considered the universal speed limit.

## 4. How does traveling at a relativistic speed affect space?

Special relativity also states that objects traveling at high speeds appear to be shorter in the direction of motion. This effect, known as length contraction, is a consequence of the time dilation effect. It means that if you were traveling at a relativistic speed, objects in the direction of your motion would appear shorter to you compared to someone who is stationary.

## 5. What happens when you return to a slower speed after traveling at a relativistic speed?

If you were to return to a slower speed after traveling at a relativistic speed, you would experience a time difference compared to someone who remained at that slower speed. This is due to the time dilation effect, which means that time passed slower for you while traveling at a high speed. This effect has been proven through experiments with atomic clocks on airplanes and satellites.