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Not really a recent thing, but the idea that supposedly if you travel faster than light, then you begin going back in time. But that doesn't make sense to me. I guess the math has to work out somehow, but it seems to me that if light has a speed, then - ignoring the logistical issues related to having the power to travel ftl - travelling faster than light would simply be that, faster than light. Or to put it another way, if it takes 8 minutes for light from the sun to reach earth, then an object travelling 2c should take 4 minutes to travel the same distance, not negative 4 minutes or however that'd work out.
The only conclusion I can come to regarding how that works out logically, is that relativity sets the time light travels to "0" regardless of time taken, because that's the only way I could see a negative value making logical sense. However it seems like that'd have its own issues, plus it implies that light instantly reaches its destination. Yet we know light has a speed and takes time to get places. It just... doesn't make any logical sense. Yet I guess the math must work out otherwise scientists would have blown so many holes in relativity that it wouldn't be used anymore.
inb4 "but causality..."
The speed of causality is inferred from the speed of light and the speed at which fields propagate in a vacuum. Causality, or the idea that cause must be observable before effect, is a human concept. Observing effect before cause doesn't break causality, it only appears to do so because we're seemingly limited to the speed of light. The reason why causality is said to have a speed (the speed of light in a vacuum) is because, with the exception of quantum tunneling, we've never observed anything that moves faster than light, so it's a seemingly safe assumption to say that cause and effect play out at a speed no greater than light in a vacuum. Or to put it another way, the speed of light dictates causality, not the other way around. If something is found to be faster than light (like particles tunneling through objects), then causality must shift with it.
Let me see if I can try to explain this.
First off, light isn't just the fastest thing we know of, it is physically impossible to go faster than light according to the laws of physics as we understand it. This is because the speed of light is actually tied to the way spacetime works.
Imagine you are standing and you throw a ball. The ball travels at whatever speed you throw it, let's say 5 mph.
Now, let's put you on a train traveling at 20 mph and do the same thing. If you throw the same direction the train is traveling, your 5 mph adds to the train's 20 and the ball goes at 25 mph according to someone standing next to the track. Throw it the other way and they see it travel at 15 mph. To you, in either case, it appears to move at 5 mph.
Light doesn't do this. We've measured it, and in a vacuum light always appears to travel at the same speed (we call it c for short). If you hold a flashlight, your friend next to you can measure the speed of light and will find it to be c. If we put you back on that train and stand your friend next to the track, you will see the light moving at c, but so will your friend. Not c +/- 20 mph, but c. Even if we put you on a rocket traveling at some significant portion of light speed, say 0.5 c, both you and your friend would still observe the light from your flashlight to be traveling at c.
This is what Einstein figured out, and this is what we mean by Relativity. From this, we also know that objects moving faster experience an increase in mass (you have to get moving pretty close to c to really notice), and as you approach c that mass trends to infinity. That's why anything with mass cannot achieve the speed of light, it would be infinitely massive, and thus require infinite energy to accelerate to that speed. Thus, only things with no mass (such as light) can move that fast.
When Zefram Cochrane is born you'll eat your words!