Comments on: Particle-particle collisions. A question. https://habitablezone.com/2011/07/22/particle-particle-collisions/ Mon, 06 Apr 2026 09:05:36 -0700 hourly 1 http://wordpress.org/?v=3.3.1 By: cjb https://habitablezone.com/2011/07/22/particle-particle-collisions/#comment-4165 cjb Sun, 24 Jul 2011 00:29:33 +0000 http://habitablezone.com/?p=2699#comment-4165 You can't exceed a relative speed of light by sending two particles crashing into each other at velocities that add up to more than the speed of light. This is what the theory of special relativity tells us, time and space change, the speed of light doesn't. Two particles traveling at 99% of the speed of light in opposite directions do not collide at 198% of the speed of light. They collide at 99%+ of the speed of light, but not more than 100%. An observer on either particle would see the other particle traveling slower than 100% of the speed of light because speed is space divided by time and both space and time are distorted on the observed particle when viewed from the reference frame of the the observer's particle. The kinetic energy, momentum and all the other physical properties of moving particles are preserved under the Einstein equations (which are different from the Newtonian equations that work for particles moving at more moderate speeds. It seems counter-intuitive, but it has been proven over and over again in real experiments with real particles and with real waves. Particle accelerators would not work at all if the velocities just added up algebraically. Neither would GPS receivers, atomic clocks, or many other devices for which relativistic corrections have to be applied to get them to work right. Newton created his physics with three assumptions that seemed perfectly reasonable at the time, but simply were not true: mass, time and space never change. Einstein made only one assumption: the speed of light never changes. Once you make that assumption, (which has never, ever been experimentally shown to be violated) then mass, space and time must vary in order for the results of certain experiments to make sense. This really sucks, because it means no faster than light travel. You can’t exceed a relative speed of light by sending two particles crashing into each other at velocities that add up to more than the speed of light. This is what the theory of special relativity tells us, time and space change, the speed of light doesn’t.

Two particles traveling at 99% of the speed of light in opposite directions do not collide at 198% of the speed of light. They collide at 99%+ of the speed of light, but not more than 100%.

An observer on either particle would see the other particle traveling slower than 100% of the speed of light because speed is space divided by time and both space and time are distorted on the observed particle when viewed from the reference frame of the the observer’s particle.

The kinetic energy, momentum and all the other physical properties of moving particles are preserved under the Einstein equations (which are different from the Newtonian equations that work for particles moving at more moderate speeds. It seems counter-intuitive, but it has been proven over and over again in real experiments with real particles and with real waves. Particle accelerators would not work at all if the velocities just added up algebraically. Neither would GPS receivers, atomic clocks, or many other devices for which relativistic corrections have to be applied to get them to work right.

Newton created his physics with three assumptions that seemed perfectly reasonable at the time, but simply were not true: mass, time and space never change.

Einstein made only one assumption: the speed of light never changes. Once you make that assumption, (which has never, ever been experimentally shown to be violated) then mass, space and time must vary in order for the results of certain experiments to make sense.

This really sucks, because it means no faster than light travel.

]]> By: VelociraptorBlade https://habitablezone.com/2011/07/22/particle-particle-collisions/#comment-4156 VelociraptorBlade Sat, 23 Jul 2011 18:58:14 +0000 http://habitablezone.com/?p=2699#comment-4156 I would imagine car crash physics would come into play here. Most people say that the combined forces of two cars of identical make crashing would be like crashing into a stationary object at the combined speed of both cars. However, <a href="http://physics.about.com/od/energyworkpower/f/energyforcediff.htm" rel="nofollow">this guy</a> makes a convincing point that this isn't true. I'm gonna have to go with what he says here. I would imagine car crash physics would come into play here. Most people say that the combined forces of two cars of identical make crashing would be like crashing into a stationary object at the combined speed of both cars. However, this guy makes a convincing point that this isn’t true. I’m gonna have to go with what he says here.

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