For the light pulse, it might help to remember that light doesn’t glow. If you had a really high-speed camera and that pulse of light zipped past you, you wouldn’t see a long, thin glowing rod moving past, because you wouldn’t see anything. You only see when light enters your eyes (or camera), and that light is headed for someplace other than your camera.
And the bit about funny addition of velocities isn’t really a distinction between light and “things”. It’s true that “things” can’t go the speed of light… but they can get awfully close. The protons in CERN’s particle accelerators are going at 99 point something percent of the speed of light, and behave almost exactly like light does as far as addition of velocities: If I put CERN on my souped-up sports car and drove forward at half the speed of light, and shot protons forwards, they’d be going at 99 point something slightly greater percent of the speed of light.
In fact, it’s not even known for sure that light really is massless. It’s possible that photons do have a mass, but it’s just really, really low compared to the energy of any photon we’ve ever measured. Given that all of our instruments have only limited precision, we can’t tell the difference.
You’re right, a thing cannot not obey the laws of physics. The issue, though, is that the laws of physics are WAY more complicated than they appear at first, and our normal range of observation only accounts for a small sliver of possible scenarios. The understanding of the universe that almost everybody has (that is to say, other than the small fraction of people who have studied physics deeply) cannot include a meaningful understanding of relativity (or quantum mechanics) because they’re just so damnably far away from our ability to observe, and so very very strange.
Please note, I’m not saying this in any derogatory sense. Different people have specialized knowledge in different areas, and therefore have deeper understanding. I couldn’t possibly identify the differences between, let’s say, 2 red wines, while a trained sommelier could.
My actual point was that a “thing” does obey the laws of physics, but light (part of electromagnetism) is not considered an object, or a thing. It’s a fundamental property of space time, and obeys the laws of physics which govern electromagnetism. It’s thinking of light as an object that makes it so hard to understand the conundrum in the OP.
Relativity isn’t actually all that hard to understand. Qualitatively, it’s all just rotations, and length contraction is no more mysterious than the fact that a broomstick is taller standing on end than it is lying on its side. Of course, there’s math to describe the details, but even there, it’s all high-school level math, and you don’t even need calculus for most of it.
Quantum mechanics, though… As Feynman once said, anyone who understands quantum mechanics doesn’t understand quantum mechanics.
I’m having a hard time understanding this. Imagine a baseball pitcher standing on the hood of a car (don’t fight it; the car is modified with a platform on the front and the pitcher has excellent balance ). The car starts in center field and accelerates and is travelling at 90mph by the time it hits the pitching rubber. The pitcher (with perfect timing) delivers a pitch that nominally travels at 90mph.
When the batter takes a swing at the pitch (and again, he’s not worried about the car crashing into him) is the ball travelling 90mph or 180mph? Somewhere it between?
Just to cut to the chase. If a rocket ship is travelling in one direction at 90% of the speed of light, and a different ship is travelling away from it in the opposite direction at 90% of the speed of light. the relative speed between the two ships will not exceed the speed of light.
When you ask what speed is the ball traveling, you have to specify “relative to whom”? The batter? The pitcher? The whole point of relativity is that times, distances, and speeds are relative. They change according to who is doing the measuring.
From the perspective of the pitcher the ball is traveling 90 mph.
From the perspective of the batter, the ball is traveling *almost *180 mph.
That’s because speeds aren’t additive. They appear to be additive in day to day life because when they’re low the other terms drop out, but they’re not.
The actual speed (from the batter’s perspective) is (90mph + 90mph) / (1 + 90mph/c * 90 mph/c).
90 mph is tiny compared to the speed of light. It’s like 1 / 7,000,000 th. So the term (1+90mph/c * 90mph/c) is equal to 1 + 1/7,000,000 * 1/7,000,000 or about 1.0000000000002 . Divide 90mph + 90mph by this and you get something really close to 180 mph, which is why it looks like you can just add velocities together.
Somewhere in between. However for this example the somewhere in between is so close to 180mph that you would require equipment of significantly advanced capability and precision to be able to measure the difference.
Works like this. (I hope, it is 2am here…)
Everyone sees themselves as moving though spacetime. You move though spacetime a c. Which is 1. Wherever you stand you move though spacetime at one second per second. But if you are the batter, and you observe the car driving at you at 90mph, you see an object that from your point of view is moving in your reference frame, and because it is moving, it can’t be moving through your view of time at one second per second, as both its speed though time and it speed though space must add to 1. So it is crabbing sideways slightly in spacetime in order to come at you at 90mph. The pitcher however also see himself in his own frame of reference, and sees himself as moving though time at 1 second per second. He sees his ball pitched forward, in his reference frame, as travelling at 90mph. But his reference frame isn’t yours. You see him, and his pitch as moving, so from your standpoint they must give away a tiny bit of their progress through time in order to be moving. This tiny bit is worked out as a simple triangle. The hypotenuse must always equal one, one side is the speed through space, and the other side is the speed though time. In order to work out the triangle you need to express c in speed through space rather than time, and it is 3x10[sup]8[/sup]ms[sup]-1[/sup] which amongst other things is how fast light travels. So it is commonly known as the speed of light.
You measure the car at 90mph in your reference frame, but the ball is pitched at 90mph in the car’s reference frame, not yours. So you won’t see the ball travelling at 90 + 90, but rather 90 + (90 corrected for the car’s movement in your reference frame). Given the difference in speeds - 90mph = 40ms[sup]-1[/sup] versus 3x10[sup]8[/sup]ms[sup]-1[/sup] the correction is miniscule.
In a related quandary, the speed of light in materials is slower than in a vacuum. this is theorized to be due to refraction, where light is “bent” as it interacts with molecules, bending around them so that the speed actually doesn’t change, the distance it has to travel does.
Or, the light is actually being absorbed by the material, which then creates slightly out of phase light itself, leading to a very complicated situation where new light is created, travelling in the same direction, and with the same frequency as the original light, but delayed. When this light reaches the edge of the material it then is travelling of course at the speed of light.
Or, when the hits an atom. It is then absorbed and re-emitted in the same direction, which takes a small amount of time.
There are two different reference frames here. For an observer A on the plain, the car is moving at some speed v (instantaneously, at a given time). For an observer B sitting in the card, the car is moving at speed 0. In reference frame B, the headlights come on, and individual photons move at speed c.
So, what speed do the photons move at in frame A? The nonrelativistic answer is just v + c, which is obviously greater than c. The relativistic answer is simply c. You’re assuming that if frame A is moving at speed v relative to frame B, then objects moving at speed v’ in frame B move at speed v + v’ in frame A. This is known as Galilean relativity, and turns out to be false experimentally. Instead, (Einstein’s special) relativity postulates than the speed of light is exactly in every frame, then works out what mathematical transformation you need in converting velocities in A to velocities in B in order to make that hold. The details are here. It may be counterintuitive, but that’s only because most familiar velocities are so far below c that the Galilean transformations quite close to the relativistic ones.
Quite the contrary; that’s exactly what you’d get if the atoms were absorbing the light and re-emitting it after a short delay. It may or may not be in the same direction; the direction of emission is going to be whatever it needs to be to maintain conservation of energy and momentum.
). The car starts in center field and accelerates and is travelling at 90mph by the time it hits the pitching rubber. The pitcher (with perfect timing) delivers a pitch that nominally travels at 90mph.