Relativity?) In this case the relative speed is actually about 0.88c, so this The FAQ entry How do You Add Velocities in Special Speeds must be added using the relativistic formula for addition of velocities. Rocket B observes his distance from A to be increasing. Rocket A relative to rocket B is the speed at which an observer in Greater than c can be observed by a third person in this way.īut this is not what is normally meant by relative speeds. My frame of reference is increasing at 1.2c. If a rocket A is travelling away from me at 0.6c in a westerlyĭirection, and another B is travelling away from me at 0.6c in anĮasterly direction, then the total distance between A and B as seen in The CherenkovĮffect is thus not considered to be a real example of FTL travel. When we discuss moving faster than light, we are really talking aboutĮxceeding the speed of light in vacuum c (299,792,458 m/s). See the FAQĮntry Is there an equivalent of the sonic boom for That medium, and Cherenkov radiation is produced as a result. Possible for particles to travel through air or water faster than light travels in Refractive index of the medium (1.0003 for air, 1.4 for water). Such as water or glass, light slows down to c/n where n is the Travels at a speed c which is a universal constant (see the FAQ entry Is the speed of light constant?), but in a dense medium One way to go faster than light is to make the light slow down! Light in vacuum
The sections are numbered so that they can be referred Many of these things are discussed in more detail elsewhere in the FAQĪnd hyper-links are provided. Finally, we will look at some of the more serious proposalsįor real FTL. Think about what we mean by non-trivial FTL travel/communication and examine some of theĪrguments against it. When FTL is being discussed, and so they are necessary to deal with. Mentioned not because they are interesting, but because they come up time and time again If FTL travel or FTL communication were possible, then causality would probably be violated and some veryįirst we will cover the trivial ways in which things can go FTL. Not inevitable that one day technology will enable us to go faster than light. That someone would one day succeed in flying faster than sound, once technology got around the problems. The truth is that some engineers once said that controlled flight faster than sound mightīe impossible, and they were wrong about that. It was known that rifle bullets go faster than sound long before anĪircraft did. They say no-one will ever go faster than light." Actually it is probably not true that anybody said it It is sometimes objected that "they said no-one would ever go faster than sound and they were wrong. The foreseeable future), but it does cover some of the more common points that are This article is not a fullĪnswer to the question (which no doubt will continue to be discussed in the newsgroups for
On the other hand, there are also good reasons to believe that realįTL travel and communication will always be unachievable. In actual fact, there are many trivial ways in which things can be goingįaster than light (FTL) in a sense, and there may be other more genuine It might be thought that special relativity provides a short negative answer to this
The moon revolves round my head faster than light! Is Faster-Than-Light Travel or Communication Possible?
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