Does My Wrist Watch Physically Beat Slower?by Kingfire Tags: relativity, speed of light, time, wrist watch 

#37
Dec2812, 11:57 AM

Physics
Sci Advisor
PF Gold
P: 5,518





#38
Dec2812, 02:46 PM

P: 36

interesting discussions.. so SR and LET are identical in mathematical formulation.
Peterdonis. Going to this example. Supposed you had a missile launched from earth travelling at 0.99c aimed at a target in Tau Ceti, and in it's frame only 2 seconds would elapse travelling to it. Supposed after 30 seconds, you have order from the President to abort it. You know you can't reach the missile using any radiowave because it can't go beyond light speed. Supposed tachyons could travel in the aether frame only and instantaneously (and normal light and matter can't). When you sent out the tachyon abort signal at 30 seconds... it should reach the missile at its 30 seconds time too right? But then by this time, the target in Tau Ceti is already destroyed at 2 seconds in the missile frame. Is this example right? Or can you reach the missile at 1.8 seconds even after you sent out the tachyons at your 30 seconds using tachyons that uses the aether frame? I don't believe in tachyons. But just want to understand the concept and limitations. 



#39
Dec2812, 03:11 PM

Physics
Sci Advisor
PF Gold
P: 5,518

(This means, of course, that in the missile's frame, the time between launch and the President issuing the order is *much* less than 30 seconds; in fact it's 30 seconds divided by the time dilation factor, which is something like 10^8, so it's on the order of a hundred nanoseconds. In that time, the missile has gotten closer to Tau Cetior, rather, Tau Ceti has gotten closer to the missileby only a very small fraction of the total distance; so in the missile's frame, the radio pulse simply has a shorter distance to travel than Tau Ceti does, so it reaches the missile first.) Of course, this depends on the Earth's rest frame being the "aether frame". However, we can make a much more general statement, because we've already proven (I just did it above) that a light pulse emitted at Earth time t = 30 seconds after launch will reach the missile before it hits Tau Ceti. But *any* tachyon pulse, regardless of how it travels, must reach the missile before a light pulse emitted from Earth at the same time, because any tachyon must, by definition, travel faster than light. So if a light pulse can reach the missile in time, then so can any tachyon pulse, regardless of the exact laws governing tachyons. 



#40
Dec2812, 03:48 PM

Sci Advisor
HW Helper
Thanks
P: 26,167

Hello Kingfire! Welcome to PF!
(are you still there? ) time dilation is only relevant between two clocks (or a clock and an observer) if they have different velocities 



#41
Dec2812, 05:10 PM

P: 36

Supposed the aether frame is not the earth's rest frame.. but somewhere out there.... is it not always the case that when the aether frame is used, 30 seconds on earth is synchronized to 30 seconds on the missile? You mean it varies depending on the location of the aether frame even when tachyon speed is instantaneous?? How do you find the location of the aether frame if you both want the earth's and missile to be both sychronized at 30 second worldline? 



#42
Dec2812, 07:28 PM

Physics
Sci Advisor
PF Gold
P: 5,518





#43
Dec2812, 07:33 PM

Physics
Sci Advisor
PF Gold
P: 5,518

Tomahoc, one other thought regarding the Tau Ceti scenario; I suggest that you consider carefully this statement I made a few posts ago:




#44
Dec2812, 07:55 PM

P: 36

Also ignore the distance is tau ceti. Imagine it is so far off that light speed is not enough to reach it because it is far. I thought tau ceti is hundreds of light years away and I'm assuming 0.99999999999c (or put any 9 where it is far enough) 



#45
Dec2812, 08:11 PM

Physics
Sci Advisor
PF Gold
P: 5,518

In my last post, I said we can figure out everything in the Earth frame; I was hoping you would pick up on that, but I'll go ahead and do it now. All quantities are relative to the Earth frame in what follows. We have a distance D to Tau Ceti, a speed v < 1 for the missile (I'm using units in which c = 1), and a time t after the missile launch when the President's order goes out. We want t to be large enough that the radio pulse emitted then from Earth can't reach the missile before it hits Tau Ceti. We assume that the missile is launched at time [itex]t_0 = 0[/itex]. The time the missile reaches Tau Ceti is: [tex]t_m = \frac{D}{v}[/tex] The time the radio pulse reaches Tau Ceti is (the pulse is sent at time t and travels at speed 1): [tex]t_r = t + D[/tex] We want [itex]t_r > t_m[/itex], which gives [tex]t + D > \frac{D}{v}[/tex] or, rearranging terms, [tex]t > D \frac{1  v}{v}[/tex] Now suppose we have a tachyon pulse that travels at speed w > 1 in the Earth frame (we don't know w's exact value, but we can still work with it as an unknown variable). We can run the same type of analysis as above to find the time [itex]t_y[/itex] that a tachyon pulse emitted at t will reach Tau Ceti: [tex]t_y = t + \frac{D}{w}[/tex] If we want the tachyon pulse to catch the missile before it reaches Tau Ceti, we must have [itex]t_y < t_m[/itex], which gives [tex]t + \frac{D}{w} < \frac{D}{v}[/tex] or, rearranging terms, [tex]t < D \frac{w  v}{w v}[/tex] So if the time t lies between the two limits given above, i.e., if we have: [tex]D \frac{1  v}{v} < t < D \frac{w  v}{w v}[/tex] then the tachyon pulse will be able to catch the missile before it hits Tau Ceti, but a radio pulse will not. I'll stop here to let you digest the above; it should give you an idea of how to calculate when each pulse will reach the missile, as well as when it will reach Tau Ceti. 



#46
Dec2812, 08:36 PM

P: 36

If instantaneous tachyons can reach the missile. And the missile sending back another signal. It can reach the earth before earth send it. This is what happen if the tachyons are frame dependent. But if the tachyons velocity which can be any speed up to instantaneous is always Fixed relative to the aether frame. Then no backward time loop possible. In this case, the tachyons signal sent out 30 secs from earth reaches the missile also at 30 seconds? Because if its earlier, it can produce a situation where earth can receive it before it sends out the signal. 



#47
Dec2812, 08:46 PM

Physics
Sci Advisor
PF Gold
P: 5,518

However, even if the signal arrives at the missile earlier than t = 30 seconds in the Earth frame, the return signal still won't arrive before it was sent, *if* tachyons always travel at the same speed relative to the aether frame. Remember that the return signal is traveling in the opposite direction to the outbound signal; that means the effect of the Earth's velocity relative to the aether frame is exactly the opposite on the return signal from what it was on the outbound signal. For example, suppose the outbound signal travels "backwards in time" by 1 second, so it arrives at the missile at t = 29 seconds. Then the return signal will travel "forwards in time" by the same amount, because it's traveling in the opposite direction; so it will arrive back at t = 30 seconds (assuming it is emitted at the same instant the outbound signal is received). 



#48
Dec2812, 08:48 PM

P: 848

However, in the context of the Lorentz Ether Theory (LET) the situation is physically different. Lorentz specifically based his derivations on the consideration of a fixed ether and the results of transmittal times between objects and within objectsall processes occuring in one time evolving 3D world. So, all observers are living in the same 3D world. Thus, the watch the moving guy is wearing (he's moving relative to the ether) is physically ticking more slowly than it would if the guy were at rest relative to the ether. However, due to Lorentzian processes affecting this guy (length contractions and time time dilations) as well as affecting the guy's wrist watch, he does not notice the fact that his clock is ticking slower, etc. Again, it should be emphasized that the basis of Lorentz's (and Poincare's, et. al.) derivations make LET significantly different than the EinsteinMinkowski theory of special relativity, notwithstanding the common mathematical feature, i.e., Lorentz transformations. It should be noted that hardly any physicists doing special relativity do it in the context of the fixed ether concept. Virtually all physicists doing relativity operate with derivations based on the EinsteinMinkowski concept. I recently reviewed several of my old text books and reference books on special relativity and found all of them following the EinsteinMinkowski formalism (Bergman, Rindler, Weyl, Naber, Baruk "Classical Field Theory", etc.). Even all of the popularizations follow EinsteinMinkowski, with only an occasional brief mention of LET. That's why I kind of feel like LET is more of a red herring to be put on the table any time someone begins to infer that the 4dimensional spacetime somehow relates to physical reality. p.s. I notice that those on this forum who present LET as though it were on a par with EinsteinMinkowski never use the Lorentz ether concept with the implied force transmittal delays, etc., as a basis for explaining the phenomena associated with relativistic speeds. They either couch explanations in the context of EinsteinMinkowski spacetime or else just do Lorentz transformation numerical calculations, avoiding any reference to underlying foundational concepts of special relativity. Not even a comparison of alternative physical concepts are considered relevant. 



#49
Dec2812, 08:55 PM

P: 36





#50
Dec2812, 09:00 PM

Physics
Sci Advisor
PF Gold
P: 5,518

However, the "block universe" interpretation, at least the strong version that has been argued here (and is also argued by certain physicists in popular books) is subject to similar criticisms, because the strong "block universe" interpretation is more than the simple claim that "4dimensional spacetime somehow relates to physical reality". It is the claim that 4dimensional spacetime *is* physical reality, period. That's a very strong claim, which also goes beyond the experimental evidence we have, not to mention that all of our current candidates for a theory of quantum gravity say it's falsethey all view 4dimensional spacetime as an emergent, approximate phenomenon, not as fundamental. (There are also issues involving determinism, which I've talked about before.) 



#51
Dec2812, 09:08 PM

Physics
Sci Advisor
PF Gold
P: 5,518





#52
Dec2812, 09:29 PM

P: 36

Anyway. How many seconds in the missile frame can it receive the earth signal which is sent at 30 seconds assuming tachyons velocity (instantaneous in our case) is fixed relative to aether frame. How do you solve for it? 



#53
Dec2812, 09:40 PM

Mentor
P: 16,489





#54
Dec2812, 10:02 PM

Physics
Sci Advisor
PF Gold
P: 5,518

As for your question, I've given you enough information already to work out for yourself under what conditions a tachyon pulse can or cannot reach the missile in time; you can work the entire problem in one frame (I worked it in the Earth frame). Have you read through the worked example I gave? 


Register to reply 
Related Discussions  
Broke my Wrist  General Discussion  17  
Why is my wrist watch sometimes cold, and sometimes warm?  General Physics  3  
MP4 Wrist watch will be fashion in short period?  Computing & Technology  0  
The Wrist Test  General Discussion  32 