Speed of Light & coffee table physics?

Question

One of my friends put forward a theory the other day which I have no idea about but found interesting. Using some formula from Einstein's theory of relativity, he calculated that if we managed to travel almost but not actually at the speed of light, time (as experienced by the body travelling at that speed) would be infinite and therefore practically stop. I have no physics background and not a clue about mathematics but was wondering if anyone out there has any thoughts/theories to back this up or prove it wrong? Thanks for any thoughts, educated or otherwise ;)

Answer 1

Since this is more or less "coffee table physics", I suggest looking back to the movie "Back To The Future." In Michael J. Fox' character (Marty), he only "travelled back" for a few seconds yet when he went to where he was "travelling", the people at his destination were years behind the "future."

So, reverse this process. Imagine then what will happen if you "travel" to the future and come back to where you were originally.

The same concept (or phenomenon, for a lack of a better description) applies. Even though you travelled for only a few seconds, the people (who did not travel with you) had to live their normal lives through so many years.

You may not even be recognized when you come back NOR will you even recognize if this were the same place that you left  "a few seconds" ago.

Time dilation is the apparent cause of all these.

Answer 2

Yeah, he's correct. As your speed increases, time slows down for you (relative to other people who are not moving). At normal speeds the effect is negligible, but as you approach the speed of light time slows down, such that at EXACTLY the speed of light, time STOPS (so if you were to travel at ALMOST the speed of light, time would ALMOST stop). I'm not sure, but if you were to travel faster than light, time would go backwards for you, relative to people who are stationary. Think of this analogy: if you were on a space ship, you leave earth in the year 2008, go on a trip at a speed faster than light, and land back on earth you'd find it's the year 2007.

In your case (traveling at below the speed of light), you leave earth in the year 2000. You go around space for a few days at almost the speed of light, then land back on earth, where you discover it's the year 2018, even though to you it's only been a few days aboard the ship. You can use this phenomenon to travel into the future...

However, if you're thinking of time travel using a spaceship, Einstein's theory throws this spanner in the works: as your speed increases, your mass also increases exponentially such that at the speed of light, your mass is infinity. What this means is that your spaceship will weigh infinity kilograms, and hence you'd need an infinite amount of fuel to accelerate to that speed, so unless you had an infinite supply of energy (like a perpetual energy machine :-) or some way to trick the universe, all this theory is quite useless...

Answer 3

This is called time dilation, but that's not quite an accurate statement of what happens. The moving body can't tell its moving, so it experiences time as normal. Somebody else who is stationary would see the moving person's time slow down. The person who is moving would see everyone else's time slow down. (The disagreements are resolved using general relativity when the they change speeds so they are moving in the same reference frame.)

Here's the formula:

t' = t*√(1-v2/c2)

Answer 4

I think it would appear to practically stop, but you would still actually age, as although time appears not to change, change would still go on. It makes scientific sense from what I know (not all that much, though a bit). Obviously it would be impossible to prove, as to get to that speed would be a considerable challenge - to put it lightly. I hope that helps :)

Answer 5

Yes, the traveller's time would slow down considerably at near-light speeds. As you're probably aware, it's impossible to achieve the speed for light for anything that has mass - its mass would grow to infinity at light speed.

Concerning the slowing-down of time, it won't be apparent to the traveller. He will simply find himself at his destination much sooner than he expected. Or, if he's on a round trip to earth, he will simply discover that time on earth went quicker than his.

Near-light-speed travel is notable for the fact that even if it takes light many thousands of years to reach across galaxies, from the traveller's point of view it will take much less time.

At the speed of light, time stops. So if we forget about the mass for a moment, travelling at the speed of light would mean instant travel - for the traveller. For the observers, travelling at the speed of light would take exactly as much as it takes for light itself to travel.

Incredible stuff, isn't it?

Answer 6

Your friend is basically correct.  Say a spaceship, traveling at 99% of the speed of light, were to leave the earth, go to an outpost 6 trillion miles away, and then stop, turn around and come back.  From our point of view, the round trip would take about 2 years.  But only about 100 days would have passed on board the ship.  The astronauts would have aged only 100 days, eaten only 100 days worth of rations, and their clocks & watches would all say that 100 days had passed.  LIfe would seem perfectly normal to them; and they would probably react with surprise to find that 700+ days had elapsed on earth (unless they knew their physics :-)

This effect ("time dilation") is more pronounced at speeds approaching the speed of light; but the effect exists at any speed.  Even when you're walking down the street, you age at a _very_ slightly slower pace than the people who are standing still.  GPS satellites--which orbit at thousands of miles per hour and which carry extremely precise clocks--must make adjustments in their clock rates to account for the effects of time dilation (if they did not, then your handheld GPS device would be off by miles).

Answer 7

No.  Einstein found that time was relative.  So even going 99% the speed of light, you would experience time exactly the same on board your ship.

If you were somehow able to observe individuals on earth, they would be going ridiculously fast and upon returning from your trip, generations may have passed (depending on your length).

The velocity of light is constant.

Answer 8

The person moving at near the speed of light would not notice anything different. Time would pass for him as normal and he would still see light approach him and travel away from him at the speed of light. However, because he is in a diffferent inertia reference, it is observers moving slower than him that would see him as being slowed down timewise. Likewise, the traveller would see his observers' time being speeded up.

In short, relativity means that we all different references of time depending on how we are moving relative to each other. This is because the speed of light appears to be the same for everyone regardless of their movement.

Answer 9

That is one of Einsteins theories. As you travel faster, time slows down. Now, at the speeds human manage to travel, the difference is so tiny its immesurable, but as you get close to the speed of light, it makes a bigger difference. Time would not actually "stop", it just would run differently for you and the outside world. Time would run normally for everyone else, but for you, it would seem to slow down. Einstein described it like this: twin babies are born. One is raised normally on earth, and the other is placed on a super fast space ship. This space ship can travel almost the speed of light. It is shot into space traveling almost the speed of light for 35 years, then turns around and comes back, same speed, for 35 years. When he gets back, the babies brother, who was left on earth, will be 70 years old. The baby, who traveled almost the speed of light, would have had time slow down for him and she ship, and he might only be a few years, or even a few months, old. Time ran normally for everyone on earth, but inside the ship itself time was running much slower. They have actually proven this concept, using two incredibly precise clocks, perfectly synchronized, and placing one on a super-sonic jet. They flew the jet around the earth a few times, and then compared the clocks. The clock that had been moving faster in the jet had had time slow down for it, and was a few seconds behind the clock left standing.

Answer 10

The speed of light in vacuo is a constnt in all ref frames moving with uniform velocity wrt each other. The 'laws of science' regarding force/acceln momentum cons etc are invariant whether the observer is at rest or moving uniformly (in fact the Galileo formulation dictates this). In order to conserve these laws and the constancy of c too, fundamental quantities like mass, length and time have to themselves vary. This is why two observers moving wrt each other experience different time durations for example (but symnetric) The relation is given by the simple L- transform.. rt(1/(1-v^2/c^2)). Actually Maxwell or even Faraday should have been able to work this out from the simple symnetry between the E and B equations, namely [curl]E=-dB/dt and [curl]B=(dE/dt)/c^2.