# Comment on awnser to "If I fire a gun at light speed..."

Well answered Cecil, but you basically said in words what the formula says in mathematical terms rather than actually explaining the phenomena qualitatively.

Welcome to the SDMB, pstils.

A link to the column you’re commenting on is appreciated. Providing one can be as simple as pasting the URL into your post, making sure to leave a blank space on either side of it. Like so: http://www.straightdope.com/classics/a2_095.html

right. along the same vague lines, is the Fitzgerald effect something that Fitzgerald figured out to fit into that equation or did he (she?) verify it somehow? maybe this is a whole nother topic, but how the heck does that work?! i find it hard to wrap my head around the fact that a force upon an object inside and pretty much independent of something else, (the bullet in the spaceship) can cause the whole thing to move slower through time. what happens at the place where the spaceship meets space? say if the spaceship in its near lightspeed velocity were to ram into a meteorite under the fitzgerald effect–what would happen and when?

maybe this is blatant hijacking, but there doesn’t seem to be much discussion anyway, so just tell me mods if anything

Let’s assume that what the formula states is: (0.9c + 0.9c)/(1 + [0.9]^2) = 0.994c
Honestly, I’m not sure that’s what it says, but I’ll let Chronos or some other near genius handle that aspect of the issue.

Cecil goes on to say:

M. Fawh Sis Myan

The bolded section offers an added insight which explains, at least somewhat qualitatively, what is happening beyond the numbers.

Cece also gives the simple answer. No.

I’m not sure what else you want.

What helped me grasp this, (if I really did), was the Michelson-Morley experiment. They tried to use light as a very precise ruler to measure how fast the Earth was moving through the “ether,” the supposed medium through which light waves were thought to travel. They figured the light waves would be shorter in the direction of Earth’s travel. What they found was absolutely no difference.

The conclusion is supposed to be that there is no ether. To tell the truth, I don’t entirely get that, but I do OK without ether (if my glow plugs are working :dubious: ).

What I do get is that light travels the same speed no matter what speed or direction you’re going. So, pick an observer distant from the Earth and consider the Earth’s velocity relative to the observer. To that observer’s eye, M&M’s apparatus got shorter when they lined it up with the Earth’s direction of motion, and so did M&M and the Earth for that matter. So M&M couldn’t see a difference.

That’s what I think “Fitzgerald Contraction” means. To the stationary observer, you, your gun, and whatever you’re shooting at are practically in the same place, along your path of motion, so the bullet has no trouble leaving the gun and hitting whatever you aim at.

The key to understanding the supposed paradoxes of relativity is to recognize that the world always looks normal in every way to yourself, no matter what you are doing. Time always passes at one second per second. Your weight never changes. If you have a scale in your spaceship, it will always read exactly as it did before your left. The interior space never changes. If you shoot a gun or turn on a flashlight, they will work exactly as they do on earth. From your perspective, nothing ever changes. Newtonian physics always describes everything you see and do.

So what’s the deal? The weirdness is a description of what an outside observer would theoretically see. It’s a thought experiment only.

That’s kind of disappointing, I know. But the universe is a big place and that allows us to see the effects more directly, in certain ways.

You can take a clock, stick it on an airplane, fly it around the world, and then remove it and compare it to a clock left at rest. If your clock is really accurate you can see that it’s running a few nanoseconds slow just as the equations predict.

Or you can look at the behavior of particles in accelerators. When they get sped up to near the speed of light, they live for much longer lifetimes.

Or even better, you can see that the universe is expanding and that the galaxies farthest away are moving near the speed of light and see how that affects their behavior. Why is that better? Because you can turn it around. If that distant galaxy is moving at .99C from our perspective, then we are moving at .99C from the perspective of that galaxy. That means we would look foreshortened to them, and our time would look compressed, and all the rest of it.

Feel anything? No, of course you don’t. Everything seems “normal”.

Relativity is never about us. It’s always about what’s happening to some other guy. But only as it appears to us. They don’t know that anything is going on. For them it’s just life. It’s us who look weird.

This seems to be the hardest thing about relativity for people to grasp. They always seem to think that people get literally physically squashed or something if they speed up. Doesn’t work that way. You’re always normal. Always. That’s the weird piece.

This has actually been done with super-accurate atomic clocks. Turns out Al knew what he was talking about.

Cecil has discussed this experiment briefly here.

The best explanation I’ve ever heard for the various relativistic effects is that everything is always travelling at c, in some direction or other. If you set up some coordinate system, and you’re sitting at rest relative to that coordinate system, you’re travelling at c in the time direction. If, instead, you’re moving relative to that coordinate system, then part of your motion is in some spatial direction, so the time component of your motion isn’t exactly c any more. In other words, time passes differently for you and for someone who’s not moving the same as you.