If you are travelling at the speed of light does your perception of time change?

Question

Also does time slow down or speed up or stop and do you continue to age??

Answer 1

As early as 1905 in his landmark paper on Special Relativity, “On the Electrodynamics of Moving Bodies”, Einstein predicted that a clock which is moved away and brought back will lag behind stationary clocks. Einstein called that result "peculiar", but the calculation is straightforward (see section entitled "Specific Example") and the example was not presented as paradoxical, despite his suggestion in the introduction to the paper that only relative motion between objects should matter. Later, in 1911, Einstein restated this result in the following form:

If we placed a living organism in a box ... one could arrange that the organism, after any arbitrary lengthy flight, could be returned to its original spot in a scarcely altered condition, while corresponding organisms which had remained in their original positions had already long since given way to new generations. For the moving organism the lengthy time of the journey was a mere instant, provided the motion took place with approximately the speed of light. (in Resnick and Halliday, 1992)


The "twins" entered the discussion in 1911 when Paul Langevin posed a thought experiment in special relativity, where one of two twin brothers undertakes a long space journey with a high-speed rocket at almost the speed of light, while the other twin remains on Earth. When the traveler returns to Earth, he is younger than the twin who stayed put. Langevin explained the different aging of the twins as follows: "Only the traveller has undergone an acceleration that changed the direction of his velocity." According to Langevin, acceleration is here "absolute", in the sense that it is the cause of the asymmetry (and not of the aging itself). Consistent with Einstein, Langevin did not suggest that there was anything paradoxical about it.

Thus, although special relativity predicts differential aging for the traveling twin as compared to the stay-at-home twin, it is not a paradox in the sense of an inherently contradictory result. The perception of paradox, referred to as the twin paradox (sometimes called the 'clock paradox') is caused by the error of assuming that relativity implies that only relative motion between objects should be considered in determining clock rates. The result of this error is the prediction that upon return to Earth, each twin sees the other as younger -- which is clearly impossible.

Consider a space ship going from Earth to the nearest star system a distance d = 4.45 light years away, at speed v = 0.866c (i.e., 86.6% of the speed of light). The round trip will take t = 2d / v = 10.28 years in Earth time (i.e. everybody on earth will be 10.28 years older when the ship returns). Ignoring the effects of the earth's rotation on its axis and around the sun (at speeds negligible compared to the speed of light), those on Earth predict the aging of the travellers during their trip as reduced by the factor , ε = (1-v^2/c^2)^1/2the inverse of the Lorentz factor. In this case ε = 0.5 and they expect the travellers to be 0.5×10.28 = 5.14 years older when they return.

The ship's crew members calculate how long the trip will take them. They know that the distant star system and the earth are moving relative to the ship at speed v during the trip, and in their rest frame the distance between the earth and the star system is εd = 0.5d = 2.23 light years ("length contraction"), for both the outward and return journeys. Each half of the journey takes 2.23 / v = 2.57 years, and the round trip takes 2×2.57 = 5.14 years. The crew arrives home having aged 5.14 years, just as those on Earth expected.

If a pair of twins were born on the day the ship left, and one went on the journey while the other stayed on earth, the twins will meet again when the traveller is 5.14 years old and the stay-at-home twin is 10.28 years old. This outcome is predicted by Einstein's special theory of relativity. It is a consequence of the experimentally verified phenomenon of time dilation, in which a moving clock is found to experience a reduced amount of proper time as determined by clocks synchronized with a stationary clock. Examples of the experimental evidence can be found at Experimental Confirmation of Time dilation.

The standard textbook approach treats the twin paradox as a straightforward application of special relativity. Here the Earth and the ship are not in a symmetrical relationship: the ship has a "turnaround" in which it feels inertial forces, while the Earth has no such turnaround. Since there is no symmetry, it is not paradoxical if one twin is younger than the other. Nevertheless it is still useful to show that special relativity is self-consistent, and how the calculation is done from the standpoint of the traveling twin.

Special relativity does not claim that all observers are equivalent, only that all observers in inertial reference frames are equivalent. But the space ship jumps frames (accelerates) when it does a U-turn. The twin on Earth rests in the same inertial frame for the whole duration of the flight (no accelerating or decelerating forces apply to him or her) and he is therefore able to distinguish himself as "privileged" compared with the space ship twin. The accepted resolution of the paradox is that a calculation different from that above must be made for the crew, a calculation which explicitly recognizes the change of reference frame, and the change in simultaneity which occurs at the turnaround.

There are indeed not two but three relevant inertial frames: the one in which the stay-at-home twin remains at rest, the one in which the traveling twin is at rest on his outward trip, and the one in which he is at rest on his way home. It is during the acceleration at the U-turn that the traveling twin switches frames. That's when he must adjust the calculated age of the twin at rest. Here's why.

In special relativity there is no concept of absolute present. A present is defined as a set of events that are simultaneous from the point of view of a given observer. The notion of simultaneity depends on the frame of reference (see relativity of simultaneity), so switching between frames requires an adjustment in the definition of the present. If one imagines a present as a (three-dimensional) simultaneity plane in Minkowski space, then switching frames results in changing the inclination of the plane.


Twins paradox Minkowski diagramIn the spacetime diagram on the right, the first twin's lifeline coincides with the vertical axis (his position is constant in space, moving only in time). On the first leg of the trip, the second twin moves to the right (black sloped line); and on the second leg, back to the left. Blue lines show the planes of simultaneity for the traveling twin during the first leg of the journey; red lines, during the second leg. Just before turnover, the traveling twin calculates the age of the resting twin by measuring the interval along the vertical axis from the origin to the upper blue line. Just after turnover, if he recalculates, he'll measure the interval from the origin to the lower red line. In a sense, during the U-turn the plane of simultaneity jumps from blue to red and very quickly sweeps over a large segment of the lifeline of the resting twin. The resting twin has suddenly "aged" very fast, in the reckoning of the traveling twin.

Answer 2

If it was possible to travel at the speed of light, your perception would remain constant. Theoretically if you were able to sufficiently surpass the speed of light you could alter your "place" in time, time itself would not speed or slow, just your relative position in it. Think of it like running up and down an escalator, in one direction you feel your going much faster, the other slower, in reality your speed is the same, only your perception of it has changed.

Answer 3

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Answer 4

In this thought experiment, we must discount all of the reasons that prohibit you from reaching the speed of light. That being said -

If you were to travel at the speed of light, your time reference would stop. You could not possibly have any "perception of time" since that would require a thought, and "a thought" requires time.

Imagine this - if you could travel at the speed of light, using your time and distance reference, you could travel across the entire universe in NO time - even if the universe were infinite!

Answer 5

Theoretically, if you could reach the speed of light time would stop. The time you witness is given by the following.
t = t0 * sqrt( 1 - v/c)
where t is your witnessed time, t0 is time in another reference frame, v is your velocity as viewed in that reference frame and c is the speed of light. As v approaches c, t approaches 0.

To answer your follow up question, if you were moving very fast according to Earth's frame of reference, the time you witness on Earth would slow. You would appear to the people on Earth to age quickly, but you would age normally in your frame of reference, while everyone else would seem to age slower.

Answer 6

The speed of light, to the light itself, is infinite due to the time dialation. If you could travel at the speed of light, the outside world would appear to age very quickly, if you could see it. To an observer, if they could see you, it would appear like your aging had slowed and stopped completely.

Answer 7

yes, as it would seem to stop.
Imagine this. If you were instantly teleported to the sun, and had an extremely powerfull telescope, the light that you see from earth would have left it 8 minutes before, so you could be looking at yourslef 8 minutes ago. there for if you were moving at the exact same speed as light, you would be seeing the same light constantly, and therefore it would appear that time stopped, allthough it didnt really.

Answer 8

for one according to one of Einstein's theories... you cannot go the speed of light. the closer you get to the speed of light the more thrust or propulsion you will need. But at the speed of light you will need infinite thrust or propulsion. but that's just theory. You would age normally and see normally except for you would be able to see light rays. light speed is just a speed like 60mph its just a speed not a magical thing that defies the laws of physics.


wow that made me feel smart

Answer 9

No, your perception of time remains the same. It is time *itself* that changes. It appears (to an outside observer) to slow down but, to you, everything stays the same. But, when you slow down and stop, you find that everyone else has aged more than you have.


Doug

Answer 10

At, or near the speed of light, time seems to pass normally to you. You would note it passes more quickly for those standing still with respect to you, if you could observe them.

Answer 11

The question is meaningless as only massless objects can travel at the speed of light. If you are traveling rapidly near the speed of light, everything looks the same to you until you look at your neighbor's clock, which will seem to be running slow. Remember, your reference frame is just as valid as anyone else's.