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What's something that recently boggled your mind?
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this post was submitted on 07 Feb 2024
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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!
The speed of light is the speed of information, including gravity, electromagnetism, and some other things I am not thinking of off the top of my head. For example, if the sun disappeared right now, the lack of gravitational pull would reach Earth at the same time as it blinked out from Earth's perspective.
Gluons, the Strong Force. Quantum Chromodynamics. As massless particles, Gluons also move at the speed of causality, although popping in and out between Quarks and moving only very short distances.
They call it the speed of light, but the alternate term speed of causality is gaining traction. Maybe because it fits as the "c" in E=mc^2, where the "c" is sometimes referred to as "constant" but actually comes from the latin "celeritas", which means "speed".
The term "causality" is a nice fit-all more recent alternative.
What if you think of it this way. If the Sun exploded right now, we wouldn’t know for 8 minutes, but if you were to leave at the same time, at twice the speed of light and traveled for 8 minutes, you would be 24 minutes away from the explosion now.
So if you travel away from the earth and view it through a telescope, you would see back in time as you flew away, since the light traveling from earth wouldn’t be traveling as fast.
That's not why relativity causes time dilation -- it's not the Doppler effect of light. If it were, then the direction of travel, not merely the speed, would be a factor.
Traveling toward an object would be forward in time since if you viewed it through a telescope you would be seeing the light sooner making it older faster.
No -- as I said before, relativity isn't caused by the Doppler effect of light. Direction of travel doesn't matter, only speed.
The twin paradox occurs in a scenario where someone travels both away and then back. They still experience time dilation when they return to the starting point, though they've traveled the same direction away and back.
https://en.wikipedia.org/wiki/Twin_paradox
Theres literally a section on how to explain the paradox (not even a potentially real thing anyways…..) Using doppler.
It doesn't use Doppler.
You don't understand how relativity works. I've seen someone make the exact same error you did, about twenty years back, thinking that time dilation was a result of the Doppler effect of light.
It would be impossible for the aging effect to arise in the twin paradox if relativity were the Doppler effect of light because in that scenario, as in that case, there is the same amount of outbound and inbound travel.
Relativity effects show up when you have two different entities traveling at different speeds relative to each other. The direction of travel does not matter. One could be traveling toward, away from, or at right angles to another.
You're trying to explain relativity just using Newtonian physics, which permits for the Doppler effect. Newtonian physics don't provide for relativistic effects. That's why relativity was such a big deal -- because it explained behavior that was incompatible with Newtonian physics.
In actuality, you wouldn’t be returning to the same place, the earth has moved through space and time itself. So none of these theories work since neither could return to the same place. Thats why they are theories….
And again, your own wikipedia source has a Doppler section…. So you are now saying your own source isn’t correct?
The twin paradox doesn't rely on that.
It's talking about compensating for the Doppler effect if the two are communicating.
You’re going back in time but you’re not going to be in the same place.
Think of a person walking on a road, you can drive past them and arrive somewhere before them.
You can’t do that while staying stationary. So you couldn’t say go back in time and see prehistoric Earth. It’s relative to when and where you are.