If the motion of an object is relative to a fixed frame/speed of light - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: September 27, 2017, 04:17:19 pm
content: One thing I never understood was how is motion of an object always relative to another object but somehow the speed of light is always constant. If you have something moving you determine this by its relation to another object. But a massive object can never approach the speed of light as it becomes too massive. But how can the speed of light be constant if motion is always relative to something else? If often wonder about matter shooting out of black holes at relativistic speeds. To that object its clock is stationary and the objects around it are moving extremely fast. But those objects have a great amount of mass because of their speed. Take away the objects they are relative to and they become stationary but they still contain a great amount of mass that's greater then if they were at rest. How does the particle know its supposed to have the extra mass?

author: JimRemington
author_rank: Regular Contributor
timestamp: September 27, 2017, 04:30:31 pm
content: Good questions!The speed of light in vacuum is not relative. It is measured to be c in all frames of reference.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 27, 2017, 04:57:44 pm
content: Quote from: Beamin on September 27, 2017, 04:17:19 pmThe particle does not need to know. The seemingly higher mass is only if you describe the particle in you reference system so that it is moving so fast. For an other observer in a reference system at a speed closer to the particle, the mass will be smaller, approaching the rest mass, if the particle is not moving fast in his system.The special thing about a black hole is, the escape velocity it so high that even the speed of light is not fast enough. So there is no simple escape from a black hole. It's only very few virtual quantum particle that might escape by chance / kind of tunneling.

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 27, 2017, 04:59:14 pm
content: Quote from: Beamin on September 27, 2017, 04:17:19 pmTime

author: Rick Law
author_rank: Super Contributor
timestamp: September 27, 2017, 06:44:32 pm
content: Quote from: Beamin on September 27, 2017, 04:17:19 pmWell, it is a hard concept to understand. Let me make an attempt and hopefully successfully so:(1) Light travelOne thing to remember is that light is not a particle that moves, light is an oscillation.Electric field induces a Magnetic field; as M field increases, E field is being used up. And, the newly created M field in turn induce a new E field as the M field will uses itself up to create the new E field. E->M, M->E, E->M...so on, so on. This cycles continues indefinitely oscillating between E and M. This oscillation is EM wave. Light is EM wave.Thus, you can see that the oscillation has its own native frequency within any particular medium. For example, light in water, how fast in water can the E field induce the M field to the extend that the E field is totally used up and only M field is left, and then how fast can the M field induced a new E field in water and used itself up to zero M energy and all E energy. It all depends on how the EM interacts with the water medium - that is, it depends on the property of the medium.(2) Particle travelre: " But a massive object can never approach the speed of light as it becomes too massive."Not just massive object gains mass. A very low mass particle traveling will gain mass. As long as the object is not mass-less, it will gain mass as it travels.The faster the particle travels, the more kinetic energy it contains, the more mass that particle has. You can thus view the added mass as the added kinetic energy.(3) Putting togetherSo, if you are a person in a medium... The rate EM self-induce and propagates depends on the medium. How fast E can induce M and M can induce E is fixed by the property of that medium. You in that medium can run, and your speed is affected by the medium as well, but how fast you move (or not move) will have nothing to do with how E and M field interacts with that medium. So, EM wave (light) is constant in that medium.Your girl-friend and me are both with you in that medium and timing you as you run.I can see you start only when the light showing to me "you started" gets to me. So, how I see you see is affected by the speed of the EM wave in that medium.The question "how quickly do I see you start?" is answered by "how much time does it take for the light (of you starting) gets from you to me." Say you are just one meter from me so the time is X.Now you begin running away from me and I am standing still. Now, correspondingly, "how much time it took you to move one million meter?" It would take more time for the light to get back to me this time. At your finish, the light has to travel 1,000,001 meters to get to me this time. The light would take (1,000,001*X) from your finish to get to me. What you timed as YOUR speed will be different than what I timed as your speed. Time dilated between you and me.Now imagine your girl-friend is also doing the timingand she is running at some lower speed behind you. What time she marked as your start/finish will depends on how fast she is running behind you.All the while, how fast that light got to me has constant speed depend solely on the medium. You can be standing still or running at 1/2C, the photon from you (EM wave) has constant speed because the speed that EM wave propagates only depends on how E and M interacts with that medium,Your girl friend timed you differently (your speed is relative to her), and I time you differently (your speed is relative to me). Yet the photon that from you to her, or from you to me, are all traveling at the speed dictated by how EM interacts with that medium.I hope this explanation helps your understanding...Rick

author: metrologist
author_rank: Super Contributor
timestamp: September 27, 2017, 06:52:03 pm
content: Quote from: Ice-Tea on September 27, 2017, 04:59:14 pmThis has something to do with the last minute, doesn't it?

author: IanB
author_rank: Super Contributor
timestamp: September 27, 2017, 06:54:01 pm
content: Quote from: Beamin on September 27, 2017, 04:17:19 pmThis is not actually true--the mass of objects does not really increase as they approach the speed of light. The idea of "relativistic mass" is a simplified explanation given by physicists to avoid getting too bogged down in equations. See various YouTube videos on the subject for a more expert explanation of why relativistic mass is not real.

author: Rick Law
author_rank: Super Contributor
timestamp: September 27, 2017, 07:01:19 pm
content: Quote from: IanB on September 27, 2017, 06:54:01 pmThat may well be, but it is not really relevant to "how come light speed is constant and others' speed are relative"However, it is important to note that the phenomenon is not just "for massive objects" but is "for any object with mass" will increase in mass.

author: IanB
author_rank: Super Contributor
timestamp: September 27, 2017, 07:03:38 pm
content: Quote from: Beamin on September 27, 2017, 04:17:19 pmSpeed is measured relative to your frame of reference. If two things are approaching each other at the speed of light, then each thing "sees" the other approaching at the speed of light. In relativistic terms, speeds do not add up using simple addition.The key idea of relativity is this: in classical (Newtonian) physics, the time measured by clocks and the distance measured by rulers are invariant, and therefore velocity is a simply a function of these two. But in relativity, time is no longer invariant, it is "stretchy". If the speed of light in vacuum is a universal constant, then something else has to give to make physics work. It turns out that time is what gives.

author: duak
author_rank: Super Contributor
timestamp: September 28, 2017, 10:39:31 pm
content: The bottom line is that time is another axis or degree of freedom and has to be considered, ergo space-time. Not being a physicist, I couldn't quite see the underlying connection in general relativity until I saw the "Mechanical Universe and beyond" lecture series in the mid 80's. Caltech has made them available on youtube:https://www.youtube.com/playlist?list=PL8_xPU5epJddRABXqJ5h5G0dk-XGtA5cZepisodes 41-44. The CGI looks a bit crufty today but it's still worth a view.

author: metrologist
author_rank: Super Contributor
timestamp: September 28, 2017, 10:47:40 pm
content: Yes, but things go much faster in the last minute...

author: rstofer
author_rank: Super Contributor
timestamp: September 28, 2017, 11:15:07 pm
content: Quote from: metrologist on September 28, 2017, 10:47:40 pmLike when I was taking an exam!