What Happens to Time When Traveling Near the Speed of Light?

[hamza]

I wanted to ask that if a person returned home after a journey at the speed of light for a little while ; what will be the time at his home. I mean would all his relatives be dead by that time or would just a second have passed.

 

[ZapperZ]

I would like to ask this person how he was able to travel at the speed of light in the first place. Who cares about what time he end up with. That's nothing when compared to his ability to break all known law of physics.

Zz.

 

[hamza]

I would like to ask this person how he was able to travel at the speed of light in the first place. Who cares about what time he end up with. That's nothing when compared to his ability to break all known law of physics.

Zz.

Hey, atleast try to give the answer. would have been better if u did'nt even reply. Cuz ur statement did not satisfy me.. I know it's not possible but still i wanted to know the answer. Reply if u can answer.

 

[Chris Hillman]

Ditto ZapperZ.

Hamza, you can't demand an answer to a nonsensical question, unless you want a nonsensical answer. This does suggest a sensible followup question, however: why does str not allow a traveler to travel at the speed of light? I suggest you try to answer that yourself (mathematically, from your knowledge of the mathematical form of the Lorentz transformations) and ask again in the Relativity forum if you can't figure it out.

 

[hamza]

I wanted to ask that if a person returned home after a journey at the speed of light for a little while ; what will be the time at his home. I mean would all his relatives be dead by that time or would just a second have passed.

 

[cristo]

A body with a non-zero rest mass cannot travel at the speed of light, so it makes no sense to ask the question.

 

[JesseM]

I wanted to ask that if a person returned home after a journey at the speed of light for a little while ; what will be the time at his home. I mean would all his relatives be dead by that time or would just a second have passed.

As cristo said, you can't travel at light speed in relativity, but we can ask what would happen if you got arbitrarily close. The answer is that by choosing a speed sufficiently close to light speed you could make the trip last as short as you wish from your point of view (a year, a day, a second), while from the point of view of people on Earth the time in years will be just slightly over the distance in light-years that you traveled (for example, if you travel 10 light years out and 10 light years back at 0.99999c, then the time on Earth would be 20.0002 years, while the time for you would be just over a month).

 

[ganstaman]

But there's an easy to answer related scenario. Let's say a man travels arbitrarily close to the speed to light and then returns home. He will have felt less time pass by than the clocks/calendars on Earth will indicate. Unless he took a really really short trip or he was going very very slow (compared to light), his relatives will all be dead.

EDIT: Seems I'm a minute too slow, and I don't even have any numbers!

 

[penguinraider]

Fair enough, no mass or waveform can break the speed of light barrier, but then how does light itself travel at the speed of light?

 

[RandallB]

I wanted to ask that if a person returned home after a journey at the speed of light for a little while ; what will be the time at his home. I mean would all his relatives be dead by that time or would just a second have passed.

Hamza
Actually your question is very easy to answer.
Hypothetically; IF a person was to travel at the speed of light straight out some distance and straight back home the age of those back at home would only be determined by the distance traveled.
That is if the travel out was 10 light years distance and returned right back home; the folks back home would have aged 20 years.

Rather simple really – the problem comes in attempting to define a time or “little while” that would pass for such a traveler! Which you did not ask or define in your question. Which is just as well, because there is no infinitely small answer for such a question because such an additional question beyond the one you asked is not possible. Current theory does not allow such travel.

For example Hypothetically IF a person was to make the same trip at twice the speed of light based on the reference frame of the folks back home, they would age only 10 years. Again simple based on speed and distance as easily measured by the home reference frame Hypothetically. Just don’t ask the age of the traveler nor how such speeds can be attended. Because current theory specifically defines such actions as not possible. Therefore not even a hypothetical answer to such a question could be given – good thing you did not ask.

 

[JesseM]

Fair enough, no mass or waveform can break the speed of light barrier, but then how does light itself travel at the speed of light?

Because it has zero rest mass.

 

[HallsofIvy]

Fair enough, no mass or waveform can break the speed of light barrier, but then how does light itself travel at the speed of light?

?? No one has said that no waveform can travel at the speed of light!

 

[Marghk]

I wanted to ask that if a person returned home after a journey at the speed of light for a little while ; what will be the time at his home. I mean would all his relatives be dead by that time or would just a second have passed.

This depends, is it just a fraction of the speed of light (as obviously nothing can travel at it bar light itself), and for how long? Either way, you can use this formula to equate Proper time to Earth's time:

t = to/sq[1-v^2/c^2

So for example, Bazza jumps in his crazy new spaceship and travels at 80% of the speed of light for 2 years. How much time would of passed on earth.

t = 2/sq[1-0.8c^2
t = 3.33 years.

So yes, people would age on Earth faster in comparison to you. See the twins paradox.

 

[DaveC426913]

I'm not sure why people are pretending to be obtuse to a new member , hazma's question may be technically invalid, but I think we can read between the lines and perhaps give him an acceptable answer.


hazma, would you accept a modification to your question to allow the person to travel at nearly the speed of light? It makes all the difference.

How much time passes on Earth while he's gone is very dependent on the length of his own journey and how near he got to the speed of light.

But if he made a very long trip, and got very close to c, he could - at least, in principle - create an arbitrarily large discrepancy between his subjective time and Earth's time. His trip might last only a year, but he could come back to an Earth millions of years older.

 

[Wonderballs]

If I we're to travel around the EARTH at the speed of near-light for 10 Earth years would i have aged 10 years?

 

[russ_watters]

If you mean you traveled for 10 years as measured by people on earth, no, you would age much less than 10 years.

 

[ganstaman]

If I we're to travel around the EARTH at the speed of near-light for 10 Earth years would i have aged 10 years?

10 Earth years as measured by a clock you bring with you, or by a clock still on earth?

If it's the former, then yes. Every minute you spend with yourself is still a minute for you.

If it's the latter, then no. I don't think this question is different than before just because you change the location of the travel. However, in case it does change things in ways I don't get, just know that I am sure of this and nothing else: if your clock says 10 years went by, then you did age 10 years.

EDIT: Hmmm, this time I was 3 minutes slow... At least I still seem to be getting answers right.

 

[Heathera152]

We Are But Energy

One thing that sticks me is the formula E=MC^2 If we could find a way to change us into energy then we could go the speed of light too. I enjoy thought questions because they free us up for what is possible with science now and I find they help me to learn. What happens at c that doesn't allow light to go faster?

 

[penguinraider]

Exactly what I've been trying to understand, heathera. :D

Now if every object of mass has it's waveform, could not an object turn into pure waveform at c, and then possibly turn into tachyons for example?

 

[pervect]

A body with a non-zero rest mass cannot travel at the speed of light, so it makes no sense to ask the question.

I'm not sure why people are pretending to be obtuse to a new member , hazma's question may be technically invalid, but I think we can read between the lines and perhaps give him an acceptable answer.hazma, would you accept a modification to your question to allow the person to travel at nearly the speed of light? It makes all the difference.

How much time passes on Earth while he's gone is very dependent on the length of his own journey and how near he got to the speed of light.

But if he made a very long trip, and got very close to c, he could - at least, in principle - create an arbitrarily large discrepancy between his subjective time and Earth's time. His trip might last only a year, but he could come back to an Earth millions of years older.

But there's an easy to answer related scenario. Let's say a man travels arbitrarily close to the speed to light and then returns home. He will have felt less time pass by than the clocks/calendars on Earth will indicate. Unless he took a really really short trip or he was going very very slow (compared to light), his relatives will all be dead.

Correct answers like this one have been given to the original question. However, it seems people aren't listening, or are not happy with the answers being given.

I don't understand what the problem is.

Rather than lock the thread, as we sometimes do when things go "off course" like this, I would like an explanation of why people do not seem to accept and/or are not happy with the above answers, which are all correct, and all say the same thing.

Perhaps people feel like it's OK to break the rules of physics if it is in the form of a question? This is an example of a logical fallacy, The fallacy of many questions, also known as a "loaded question".

Another example of this sort of fallacy is the "question" "When did you stop beating your wife"?

 

[StatusX]

One thing that sticks me is the formula E=MC^2 If we could find a way to change us into energy then we could go the speed of light too.

Yea, you could theoretically convert all the mass in your body into photons, and then "you" would be traveling at the speed of light. You could also convert your mass into a liquid and violate the law that humans don't conform to the shape of the containers they occupy. I don't see the point.

What happens at c that doesn't allow light to go faster?

A photon doesn't speed up to c and then hit a wall, it always travels at c. If you have a hard time separating the permanence of this fact with the idea of a photon as an ordinary moving object, just visualize photons as lines in spacetime: they don't move, they don't speed up or slow down, they just happened to be oriented at a certain, constant angle.

 

[HallsofIvy]

Yea, you could theoretically convert all the mass in your body into photons, and then "you" would be traveling at the speed of light. You could also convert your mass into a liquid and violate the law that humans don't conform to the shape of the containers they occupy. I don't see the point.

I believe that StatusX's point is that, doing either of those things, you would be DEAD!
It it fairly easy to convert your mass into a liquid (use a strong enough acid). Converting all of your mass into energy would be harder. I suspect it would involve standing at ground zero during a really strong nuclear explosion. If we assume we have space travel before doing this, you could probably accomplish it by diving into the sun.

 

[lightarrow]

One thing that sticks me is the formula E=MC^2 If we could find a way to change us into energy then we could go the speed of light too. I enjoy thought questions because they free us up for what is possible with science now and I find they help me to learn. What happens at c that doesn't allow light to go faster?

What happens is that time is not actually independent from space ((cdt)^2 - dx^2 - dy^2 - dz^2 is invariant), so, our common definition of velocity stops having the intuitive meaning it has at low speeds. In other words: for someone traveling at very high speeds, it would be more intuitive to speak of the concept of "rapidity" instead of "velocity", and the rapidity approaches infinity when your velocity approaches c; in other words, what you would see at very high speed is that planets, stars, gas or powder clouds, every object approaches and passes by you with always decreasing time, without limit, as if your speed would approach infinity.

For this reason our "common" definition of velocity is not very good, from an intuitive point of view, at very high speeds. The definition: v = delta(S)/delta(t) has is right intuitive meaning as long as space S is independent of time t, but as I said this is less and less true increasing the speed.

 

[Heathera152]

Thank you everyone for your replies, I enjoy being able to chat in a unstructured way and explore something from many angles.

lightarrow;
I found the formula v = delta(S)/delta(t) interesting. So if I am understanding it in order to go faster you would need to cause (S) to get bigger or (T) to get smaller or both. By the way what is (S) measured in? What causes the depends of space with time at high speed?

StatusX
"visualize photons as lines in spacetime: they don't move, they don't speed up or slow down, they just happened to be oriented at a certain, constant angle."
I forgot that light is a constant not something that change speed. But when light is bent around a planet wouldn't that change its speed? Or is that only for matter?

Heather

 

[lightarrow]

Thank you everyone for your replies, I enjoy being able to chat in a unstructured way and explore something from many angles.

lightarrow;
I found the formula v = delta(S)/delta(t) interesting. So if I am understanding it in order to go faster you would need to cause (S) to get bigger or (T) to get smaller or both.

Yes; at low speeds you can fix S and decreas t as you like, or fix t and increase S as you like (as long as S/t is <<c); at high speeds you can't do it anylonger.

By the way what is (S) measured in?

Metres. What else?

What causes the depends of space with time at high speed?

Good question!

 

[Heathera152]

lightarrow
Maybe space and time are always connected but it isn't as noticeable at slower speeds.

Anyone
If light is bent around a planet it is traveling a slightly longer distance then the light that travels past the planet but isn't bent by it, would this not cause a difference in the speed between the light that was bent and the light that wasn't bent?

Heather

 

[huyen_vyvy]

in your reference frame, no. Time ticks slower in your ref frame, t= 10years/ sqrt(1-v2/c2)
for the original question, I think if a person was to travel at the speed of light, then it's impossible that "after 1 second" makes sense in that ref frame. I mean, in his ref frame, NO TIME has passed. In Brian Greene's words: "photons never get old"...

 

[Mentz114]

Anyone
If light is bent around a planet it is traveling a slightly longer distance then the light that travels past the planet but isn't bent by it, would this not cause a difference in the speed between the light that was bent and the light that wasn't bent?

Heather

The light going close to the planet would be delayed compared with light that traveled from the same point to the receiver if the planet wasn't there. That's a clumsy sentence but I think about right. Experiments have been done to measure the delays caused by large bodies in the solar system.

But light speed is always measured the same by local observers. It does not make a lot of sense to talk about the speed of light somewhere/somewhen else because we cannot measure said speed.

 

[Ascending One]

I believe that StatusX's point is that, doing either of those things, you would be DEAD!
It it fairly easy to convert your mass into a liquid (use a strong enough acid). Converting all of your mass into energy would be harder. I suspect it would involve standing at ground zero during a really strong nuclear explosion. If we assume we have space travel before doing this, you could probably accomplish it by diving into the sun.

I don't think you'd have to do anything that extreme... you could simply write down all of the information contained in your body on an extremely large piece of paper (or a computer disc). Then shine some light on it... and then have someone look at it (with a powerful telescope) from (if such a place existed) a planet 10 light years away. They could then collect that information and recreate you (with some sort of futuristic machine). In that manner you could travel at the speed of light, 10 light years away without dieing.

 

[Xori]

I don't think you'd have to do anything that extreme... you could simply write down all of the information contained in your body on an extremely large piece of paper (or a computer disc). Then shine some light on it... and then have someone look at it (with a powerful telescope) from (if such a place existed) a planet 10 light years away. They could then collect that information and recreate you (with some sort of futuristic machine). In that manner you could travel at the speed of light, 10 light years away without dieing.

I disagree that this would be equal to traveling at the speed of light. This is simply a copy of you reconstrcuted somewhere, not the original you. If it is you, then you are capable of being in more than one place at the same time (the original you is here and the recontructed you is on the other planet)