# What happens to time when you travel at lightspeed?

#### campbelp2002

##### New member
It stops. But you can't really do that.

#### Toolkit

##### New member
The faster you go, time appears to go slower for you than it does for people standing still. This is called time dilation. The reason for this has to do with how light works and how certain laws of physics need to compensate to explain how light works. If you are comfortable with algebra 2, I suggest reading about relativity. The link below should be specifically helpful.Also, going faster than the speed of light does not make you go backwards in time. According to special relativity, going faster than the speed of light corresponds to you having imaginary mass ( by imaginary, I mean sqrt(-1) complex numbers imaginary), imaginary momentum, and negative energy. None of this would be observable from the "real" universe and hence is meaningless.

#### Topher

##### New member
Mass intreases as velocity increases, at the speed of light mass becomes infinite (which is why light is the only thing that travels at light speed because it has no mass)*. Also, because time is relative to velocity, (that is closer the the absolute velocity you travel, the closer to standing still time passes for you) some people hypothesize that if you could maintain near-light-speed for an extended period of time (say, in a space ship) and then slow down again, a lot of time would have passed for everyone else but only a little for you, and so it would have the effect that you "traveled into the future" but, not really. It's less like you traveled through time and more like time traveled around you.For most things, velocity is relative (for example you may be sitting still in your chair, relative to the surface of the earth... but the earth is rotating around its axis [meaning you are rotating with it] and the earth is rotating around the sun, etc... so when you're standing sill you're actually going extremely fast (relative to the rest of the universe, that is)). But light is different, light always travels at the same speed, because it is unaffected by the restrictions of mass. That's what they mean when they say time is relative, too... time is relative to velocity... maybe that's a bad explaination but... it's very tricky.*by "light" I mean any form of electromagnetic radiation (radio, microwaves, ultra-violet, etc.)

#### ever p

##### New member
At 299,792,458 meters per second time should stop. Once you start going faster then light then you will in theory go backwards in time. Time will be observed differently depending of you position. Let say that you are in a space ship. You are traveling towards another space ship at 90 % the speed of light and coming your way is another ship coming at 90% the speed of light. Then depending whether you are the observer, observing the two ships or if you are on one of the ships, time will seem different to each individual.

#### JAMES

##### New member
It is said that the time is stopped

#### Chris

##### New member
If you were to travel at close to light speed, you could not detect a difference in time, however someone observing you would see that your time is slow.While relativity states that it would be impossible to travel at light speed, time travel itself is not impossible. Time travel could be possible using wormholes, which I have no undertanding of but you can check it out here:http://en.wikipedia.org/wiki/Wormhole

#### Simplicimus

##### New member
It is impossible for massive particles to travel at the speed of light (at least with a finite time of acceleration). However, as you approach the speed of light an stationary observer will measure that your time slows down relative to his.You can ask what happens when you travel faster than the speed of light and start talking about time travel but this is completely theoretical and is not physically possible. Faster than light travel results in weird things like cause happening after the effect. This is illogical. Therefore, faster than light travel is either impossible, or relativity is wrong and some new physics takes over at faster than light speeds.Most proposed time travel "methods" rely on using some exotic curved spaces (for example wormholes).

#### Kenny

##### New member
First, there is absolutely no evidence that time travel is possible, if you are referring to the freedom to move into your relative future or past.Secondly, as objects approach the speed of light, they begin to experience noticeable increases in kinetic energy (simplified in non-relatvistic physics to E = 1/2 m v^2), which is measured by others outside of that object's reference frame as an increase in mass, as others have noted. The equation E = m c^2 talks about how much total energy any object with mass has WHEN IT IS AT REST in its environment. It has NOTHING to do with its movements relative to the speed of light.Now, as any one rest frame accelerates away from another rest frame, time begins to move at different rates between the two. The one accelerating, for instance, a spaceship, still experiences normal time and mass INSIDE the environment, but to anyone outside that environment (still on earth, for example), the time inside the spaceship seems to drag out, so that one second on earth is faster than one second on the spaceship.The people/machines/animals on the spaceship still experience normal time flow while in the spaceship, so time appears to pass normally, while thousands, or, if they are moving close to the speed of light, millions of years will pass on earth.If a spaceship were to travel from Earth to Andromeda galaxy at 85% of the speed of light, the astronauts would experience about 28 years to get there, but the earth would experience over 2 billion years.Now, taking this to the extreme of travelling at the speed of light, time outside the environment stands still. If you could travel at the speed of light, you would still experience time as you normally do, but the rest of the universe would appear to be standing still.Now, is faster-than-light travel possible? Not by normal means. There are theories about compressing space gravitationally to allow a ship to pass thru the space that has been compressed faster than the light that was IN that space when it was compressed, but this is still way beyond testing. We need to learn to create gravity, and we are still a LONG way from that point.In short, travelling at the speed of light is not physically possible if you have mass. If you have mass, you can always go faster towards the speed of light, but your mass appears to increase to observers outside your environment, and this means you would need to overcome the inertia to move faster. At the speed of light, any massed object has infinite mass, requiring infinite energy to get there. As you move closer to the speed of light, time for the REST of the universe appears to slow down, but your time still proceeds as normal.

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