I’ve been reading up on quantum physics. I don’t really understand it, but what I have been reading about is how there may be a “pilot wave” that can travel faster than the speed of light. This would be significant, as there is a theory that suggests nothing (especially information) can travel faster than the speed of light.
Would my “giant rod” proposed below, allow information to travel faster than the speed of light? Obviously not, but why…?
My giant rod is 10,000 km in length. There is a person standing at either end of the rod, which is lying on a flat surface. I pull on the rod at one end, while at the same time, shine my superpowered torch in the direct of person 2. What does person 2 see first. The light from my torch, or the rod moving?
Information would be transmitted along your rod as a wave of compression/tension, at what amounts to the speed of sound in that material. They’d see the light first, after the appropriate delay.
I’m not sure about these pilot waves though - I’ll have to read up on that one - but every year or so, there seems to be a sensational article to the effect “scientists break light speed barrier!”, but as far as I know, it’s always actually the case that they just played some clever trick that made it look that way, when in fact nothing, not even information, was travelling FTL.
We had a thread the other day that mentioned that in some materials the speed of sound can get very high indeed, imposing a theoretical upper limit on the mass of a neutron star (the point at which the neutronium is compressed enough for the speed of sound to approach c).
This might be a nitpick or, more likely (knowing Mangetout), an elaboration, depending on what he means by “appropriate”. But, some less physics-aware readers might miss that what the “appropriate delay” is for the other person to see your light depends on who is measuring the delay. In the limit as their speed relative to you and your partner approaches c, some observers see no delay, and some see a very long one. The problem is that there is no unique correct interpretation of the time delay between two events happening in different locations. We are accustomed to treating time as if it is happening the same way everywhere, but it’s actually a local phenomenon, and applying your version of time to someplace other than where you are is more complicated.
Oh, one other point. You can get things to move faster than c, if your definition of “thing” is relaxed enough. You just can’t do it with anything having mass or energy or information (all of which are different embodiments of the same underlying agency).
If you stand at the center of a big spherical room and play a laser pointer on the wall, and if you pivot the pointer fast enough and the room is big enough, the point where the beam hits the wall can move faster than c. Interestingly, other observers of this, if they are moving fast, can see that point disappear and reappear later, or see it exist in an odd number of locations simultaneously. The light traveling along the beam will always be moving at c (no matter who measures it). You can do a similar experiment with a garden hose spraying a stream of water through a nozzle. The spot where the water hits the ground can move faster than the water itself. For instance, if you manage to get a helix of water that is almost horizontal around you, it will hit the ground almost simultaneously.
What you can’t do with the laser pointer in the room is to move light from one point on the wall to another at a speed greater than c (or less, for that matter). And you can’t move information or matter or energy from one point to the other at greater than c (though for these less than c is possible).
