SR and a lightbulb
in [Relativity]
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From: Inertial on 7 Jan 2010 19:49 "train" <gehan.ameresekere(a)gmail.com> wrote in message news:7c9ad0f4-b028-4949-9a3f-305fc195c68c(a)e37g2000yqn.googlegroups.com... > On Jan 8, 4:13 am, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: >> ..@..(Henry Wilson DSc) wrote: >> > On Thu, 7 Jan 2010 12:55:33 -0800 (PST), PD <thedraperfam...(a)gmail.com> >> > wrote: >> >> >>On Jan 7, 2:41 pm, ..@..(Henry Wilson DSc) wrote: >> >>> On Thu, 7 Jan 2010 06:54:28 -0800 (PST), PD >> >>> <thedraperfam...(a)gmail.com> >> >>> wrote: >> >>> >On Jan 6, 6:29 pm, ..@..(Henry Wilson DSc) wrote: >> >> >>> >This has nothing to do with what humans see. This is a matter of >> >>> >whether the barn door strikes the pole or not, which can be recorded >> >>> >with or without humans present. >> >> >>> >Now: At the time when the front of the pole hits the back wall of >> >>> >the >> >>> >barn, what happens to the back end of the pole AT THAT INSTANT? >> >> >>> At any particular instant...or if time diesn't even exist ...the two >> >>> ends of the pole are separated by the same absolute spatial interval. >> >> >>I'll be a little more precise: At the instant when the motion of the >> >>front of the pole stops as it hits the back wall of the barn, what >> >>happens to the motion of the back of the pole? >> >> > It stops instantly as well. Reality doesn't rely on what humans see. >> >> Really? Instantly? >> >> [...] > > We this is indeed the point. Can anything travel faster than light? > When the pole hits the back of the barn door and stops instantly, Which means its a pretty tough barn door :) > the > impact has to be transmitted through the pole atom by atom. Can this > happen faster than the speed of light? In classical mechanics yes It usually happens at what is usually called the speed of sound for that material .. the speed that such compression 'information' is transmitted through the material. If this immovable barn door is trying to travel through the rod (from the moment of collision) at faster than the speed of sound in that rod, it will cause catastrophic damage to the rod, as its back end tries to plough on forwards and compress the rod faster than it can handle. This effect is the same in principle whether SR or classical mechanics. > In SRT if you follow it, you will have two effects The instant the > pole stops, You mean the instant the front end of it stops. In the pole frame, the back end is blissfully unaware that its front end has crashed into a carelessly closed barn door. > the length contraction disappears, atom by atom along the > length of the pole Yes .. as those atoms get slowed down > at the speed of light. Well. it all depends on what happens to the various bits of the rod. Its certainly not going to be good for it. Certainly the information (in SR) cannot get to the back end of the rod FASTER than the speed of light. it would probably get there at the maximum of the speed of sound in that material, and the speed of the barn wrt the rod (ie either the compression wave thru the rod gets to the back of the rod first, or the barn door itself does :)) > as the stopping of the pole also takes place at the speed of light > atom by atom. > The pole will then pop right out of the front of the Barn Door. More likely it will compress and shatter under the stress. We're assuming a very strong barn door here. > All > this for the farmer watching the pole fly through the barn door at > close to the speed of light. Life is pretty dull on a farm .. you need al lthe entertainment you can get.
From: eric gisse on 7 Jan 2010 19:53 train wrote: [...] > > We this is indeed the point. Can anything travel faster than light? > When the pole hits the back of the barn door and stops instantly, the > impact has to be transmitted through the pole atom by atom. Can this > happen faster than the speed of light? In classical mechanics yes Yeah, for infinitely rigid objects which requires atoms to transfer information faster than light speed. Which is physically impossible, and is the point of the 'paradox'. Ralph does not understand this, nor does he care to expand his mind a tiny little bit and consider the possibility. > > In SRT if you follow it, you will have two effects The instant the > pole stops, the length contraction disappears, atom by atom along the > length of the pole, at the speed of light. > as the stopping of the pole also takes place at the speed of light > atom by atom. > The pole will then pop right out of the front of the Barn Door. All > this for the farmer watching the pole fly through the barn door at > close to the speed of light.
From: Androcles on 7 Jan 2010 20:51 "eric gisse" <jowr.pi.nospam(a)gmail.com> wrote in message news:hi5pqa$ibd$2(a)news.eternal-september.org... > ..@..(Henry Wilson DSc) wrote: > >> On Thu, 7 Jan 2010 12:55:33 -0800 (PST), PD <thedraperfamily(a)gmail.com> >> wrote: >> >>>On Jan 7, 2:41 pm, ..@..(Henry Wilson DSc) wrote: >>>> On Thu, 7 Jan 2010 06:54:28 -0800 (PST), PD <thedraperfam...(a)gmail.com> >>>> wrote: >>>> >On Jan 6, 6:29 pm, ..@..(Henry Wilson DSc) wrote: >> >>>> >This has nothing to do with what humans see. This is a matter of >>>> >whether the barn door strikes the pole or not, which can be recorded >>>> >with or without humans present. >>>> >>>> >Now: At the time when the front of the pole hits the back wall of the >>>> >barn, what happens to the back end of the pole AT THAT INSTANT? >>>> >>>> At any particular instant...or if time diesn't even exist ...the two >>>> ends of the pole are separated by the same absolute spatial interval. >>> >>>I'll be a little more precise: At the instant when the motion of the >>>front of the pole stops as it hits the back wall of the barn, what >>>happens to the motion of the back of the pole? >> >> It stops instantly as well. Reality doesn't rely on what humans see. > [...] > > [...]
From: Androcles on 7 Jan 2010 21:47 "eric gisse" <jowr.pi.nospam(a)gmail.com> wrote in message news:hi5vmd$q4k$2(a)news.eternal-september.org... > train wrote: > [...] [...]
From: Androcles on 7 Jan 2010 23:50
"Henry Wilson DSc" <..@..> wrote in message news:lbadk5tiq3l4cpnagmft2rnivbl3jmo1io(a)4ax.com... > On Fri, 8 Jan 2010 01:51:50 -0000, "Androcles" > <Headmaster(a)Hogwarts.physics_r> > wrote: > >> >>"eric gisse" <jowr.pi.nospam(a)gmail.com> wrote in message >>news:hi5pqa$ibd$2(a)news.eternal-september.org... >>> ..@..(Henry Wilson DSc) wrote: >>> >>>> On Thu, 7 Jan 2010 12:55:33 -0800 (PST), PD <thedraperfamily(a)gmail.com> >>>> wrote: >>>> >>>>>On Jan 7, 2:41 pm, ..@..(Henry Wilson DSc) wrote: >>>>>> On Thu, 7 Jan 2010 06:54:28 -0800 (PST), PD >>>>>> <thedraperfam...(a)gmail.com> >>>>>> wrote: >>>>>> >On Jan 6, 6:29 pm, ..@..(Henry Wilson DSc) wrote: >>>> >>>>>> >This has nothing to do with what humans see. This is a matter of >>>>>> >whether the barn door strikes the pole or not, which can be recorded >>>>>> >with or without humans present. >>>>>> >>>>>> >Now: At the time when the front of the pole hits the back wall of >>>>>> >the >>>>>> >barn, what happens to the back end of the pole AT THAT INSTANT? >>>>>> >>>>>> At any particular instant...or if time diesn't even exist ...the two >>>>>> ends of the pole are separated by the same absolute spatial interval. >>>>> >>>>>I'll be a little more precise: At the instant when the motion of the >>>>>front of the pole stops as it hits the back wall of the barn, what >>>>>happens to the motion of the back of the pole? >>>> >>>> It stops instantly as well. Reality doesn't rely on what humans see. >>> >>[...] >>> >>> [...] > > Gawd! It's quiet in here... I'm chatting with Gisse. |