Why is it that the closer you get to the speed of light the slower time goes. And what prevents you from surpassing the speed of light? Do you freeze and are unable to move? Thank you, please forgive me if this is a lamo question, I have not taken physics yet.
Of course, I’m only slightly less of a lay-man than you. (Just finished second semester AP Physics.)
Basically, time slows down as you approach c(c is shorthand from teh speed of light) because c is a constant.
Let’s do what Einstein called a Gedankin(sp?) or “Thought” experiment.
Some guy, call him Ed, is on a flatbed train going down a mirrored tunnel. He shines a laser straight up. The ceiling is a hieght “d” above him. So the amount of time(t) the light takes to get back to him is t=2d/c. Does that makes sense to you?
Now let’s introduce an observer, Cecil. Cecil sees that the train is moving, at a speed V that covers L meters in S seconds. S seconds is defined as the amount of time it takes Cecil to see the laser go from Ed, to the ceiling and come back. Still with me? So Cecil sees the relationship:
L=VS
But L and d are related, because they’re sides of a right triangle. The laser is covering a distance that is the hypotenuse of that triangle, from Cecil’s perspective, in time S, at velocity c. (I know it’s getting complicated)
If time wasn’t variable, S and t should be equal. But they aren’t. After some algebra (That is next to impossible to post, but I’ll try if you want) you find that
S=t/square root of(1-(V[sup]2[/sup]/c[sup]2[/sup]))
This has two properties.
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The denominator will always be less than one, so S will always be bigger than t. Less time passes for Ed than Cecil.
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V can never be bigger than c without the bottom falling out of things. (Try the equation with V=5c)
The reason you can’t attain c is even more complicated, and I’ll save it for another post. (Or poster)
–John
who hopes he didn’t confuse you TOO much
This topic should have started before I handed in my Philosophy assignment on Time Travel Paradoxes…hehe…oh well.
Actually, u might like to consider reading about the Twins Paradox…which in summary, discusses how a pair of twins where one stayed on earth, while the other orbitted around earth at high speed - on returning to earth this twin you will find has aged less than the one that stayed on earth.
As to your topic heading, how does time relate to speed?
Well I guess you’d probably just have to consider time as the fourth dimension to space (the usual three dimensions we are used to).
Sorry, getting a bit sleepy, so probably not making much sense…
Yue Han’s post is correct, but perhaps some amplification is in order.
The “principle of relativity”, or “Einstein’s first postulate”, was stated by the Man himself as:
“… the same laws of electrodynamics and optics will be valid for all frames of reference for which the laws of mechanics hold good. We will raise this conjecture (the purport of which will hereafter be called the Principle of Relativity) to the status of a postulate, and also introduce another postulate . . . namely that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body. These two postulates suffice for the attainment of a simple and consistent theory of the electrodynamics of moving bodies based on Maxwell’s theory for stationary bodies.”
The first part of this can also be stated as “The laws of mechanics, electrodynamics, and optics are the same no matter what your state of motion is”. This certainly sounds reasonable, and has been borne out to be true in literally thousands of experiments specifically designed to determine if it is not true.
The second postulate (“light is always propagated in empty space with a definite velocity c”) turns out to be derivable from the first postulate, and does not need to be an axiom (as Einstein originally had it). The fact that the laws of physics are the same in all reference frames leads to the fact that the speed of light in empty space is constant for all observers.
You might want to look at How Special Relativity Works and maybe Is The Speed of Light Constant?.
Yue Han pretty much has it right on the money, but since I can’t resist posting to a relativity thread 
, I’ll elaborate a bit. The key point is that the speed of light is the same as measured by all observers, no matter at what speed they are moving. This may seem a bit counterintuitive, but it’s been proven experimentally, and follows theoretically as well. Since different observers measure the light to be going different distances, the times that they measure must also be different, to make the speeds equal.
Also, if you’re in a spaceship going at .999999 c relative, say, to the Galaxy, everything will seem perfectly normal to you on the ship, but the rest of the Universe will appear all scrunched up, and with messed up clocks, etc. If you then kick on your engines, it’ll appear to you that you’re accelerating a good bit, but relative to the rest of the Universe, you’re still going less than c. It’s not like you slam into a brick wall or something if you try to reach c, you just never quite get there.
An indespensible tool for figuring out scenarios involving special relativity is the Minkowski space-time diagram. This looks like a reasonable introductory explanation. You can find many more articles and papers on them here.
Ok, I kindof get what you are saying. But say you are on that spaceship traveling at .999…c. What prevents you from running foreward to push you up over c? Or will it just appear as if you are going faster, but you really won’t? Thank you again, I can’t wait to be taught all this in school.
Another point to be aware of: as velocity increases, so does mass. Since acceleration is related to mass and force in the classical equation F=ma, it takes more force to accelerate due to the increased mass. As v approaches c, m approaches infinity. So, accelerate to the speed of light, you would have to apply an infinite force.
The laws of the universe {grin}.
If you could kick yourself up over c, then all sorts of ridiculous consequences would follow. Of course, there’s no law that the universe can’t be ridiculous (look at quantum mechanics, for example). But if you could go faster than c, then thousands and thousands of experimental observations are wrong, and that’s pretty unlikely.
Those experiments include accelerating electrons and protons and the like to speeds like 0.9999c … you can keep pumping energy into them, and their speed gets closer to c, but it indeed never gets there.
One way of looking at it is that mass increases as your velocity increases; when you pump energy into something going close to c, most of that energy goes into mass instead of velocity. As you get closer to c, more energy goes into mass.
Why this should be so is a difficult question, and I can’t offer an answer.
To add to the previous answers, the basic theoretical reason you can’t go faster than c is that the speed of light is the same in all inertial frames of reference. Say you’re in a spaceship heading away from earth at 0.9c. Someone on earth shines a beam of light in your direction. Galilean relativity would predict that you would see the beam of light go past you at a speed of 0.1c, but that’s not the case. You see it pass you at the speed of light, the same as if you weren’t moving away from earth at all. So no matter how fast you go, you’ll never be able to catch up with light.
This fact arises naturally out of electrodynamics, specifically Maxwell’s equations (which, along with special relativity, can be derived from Coulomb’s Law and Galilean relativity). The speed of electromagnetic waves (i.e. light) can be predicted from Maxwell’s equations. You find that when you apply a coordinate transformation to the equations, that speed doesn’t change–this is the theoretical analogue of the situation above.
This is where the Lorentz transformations come from. The Lorentz transformations were known to apply to the electromagnetic field before Einstein came along; what Einstein did was to convince everybody that the Lorentz transformations applied to mechanics as well.
That’s special relativity in a very small nutshell.