md65536

Why isn't it possible? If A and B have an initial relative velocity, and are slowed by friction while in contact, what other force acts in the line of motion? I'm not sure, but speaking of "A's rest frame" and B's sounds suspicious. Each changes velocity, so which rest frame are you talking about? Before, or after the acceleration? From an arbitrarily chosen rest frame, if m_A != m_B, then A and B don't have an identical change in velocity relative to the observer.

The Lorentz transformation for time can be used to determine whether two events are simultaneous (according to standard simultaneity) in a particular inertial reference frame. The relativistic Doppler equation can be used to determine whether two events appear simultaneous from a particular observer viewpoint. (The appearance of simultaneity doesn't depend on a simultaneity convention. Two events that appear simultaneous will do so whether you call them simultaneous or say they're separated by a transit time of light.)

Why? If you assume that standard simultaneity is physically correct, then it is impossible in SR. However if you don't, and instead suppose that apparent simultaneity is possible, you can still obtain a model that is consistent with SR. (I make no claim that SR is wrong in any way, only that the classical assumption that defines simultaneity is superfluous.) Is it physically impossible for an effect to be simultaneous with its cause, or is that only a consequence of how you define simultaneity? Some philosophers have argued reasons why it is impossible (eg. a symmetrical relationship between observers must be maintained, or instantaneous "action at a distance" is absurd), but those reasons don't hold up. The reason to accept any such arguments as far as I've seen, is the assumption that they're true. But if you don't assume that they're true, you can still produce a model which makes predictions identical to those of SR.

Does this mean that the rotating clock ticks faster than the lab clock?

Yes. Do you know the answer?

What is the answer then?

Oh brother. It's the Lorentz transformation of time. [math]t' = \gamma (t - xv/c^2)[/math] for relative movement along the x-axis. I don't see how that is at all relevant. I was speaking of interpretations of QM involving "spooky action at a distance", which depends on simultaneity convention.

Well there are two things. One is "In physics, the relativity of simultaneity is the concept that distant simultaneity – whether two spatially separated events occur at the same time – is not absolute, but depends on the observer's reference frame." (http://en.wikipedia.org/wiki/Relativity_of_simultaneity) Two is, the mathematical formulation of that concept according to SR. What term should be used to describe an alternative simultaneity convention in which simultaneity is also relative? ... if not "relativity of simultaneity"? Yes, this alternative is not mainstream, but the paper is consistent with SR. What I'm doing is showing that the alternative simultaneity is consistent with the predictions of SR, AND that the postulates of relativity can be interpreted to allow it, which I think is novel. Right, well when I spoke of "standard simultaneity vs apparent simultaneity" you said I was speaking of RoS. The former statement ("an example supernova millions of light years away that is seen now occurred millions of years ago") corresponds with standard simultaneity, while the latter ("a supernova seen now is occurring now") corresponds with apparent simultaneity. The paper is about the choice of definition of simultaneity. The relativity of either choice of simultaneity is not questioned here (it can be assumed along with the rest of SR). What is PoI?

The Lorentz transformations don't consider delay of light. They give you what is "measured" in SR, and what is "seen" can then be calculated by considering delay of light. For example, if you take Lorentz time dilation and include delay of light you get the relativistic Doppler effect. I agree that the Lorentz transformations have proven totally adequate, but surely it is not a fact that there is no room for possible improvement, or for other consistent models with their own benefits? I don't quite get exactly what you're speaking of when referring to "relativity of simultaneity" because it doesn't match what I'm speaking of. If events can't be absolutely simultaneous (with simultaneity agreed upon by all observers), then there must be relativity of simultaneity, correct? And absolute simultaneity is logically impossible in SR, correct? Then isn't relativity of simultaneity a requirement of SR at relativistic speeds? How can you have SR without relativity of simultaneity? When you say "relativity of simultaneity" do you mean only the specific convention that is used to specify simultaneity in SR? When you say it isn't testable do you mean that there is no test to rule out other conventions? Or do you mean that whether two observers agree or not on the simultaneity of two events makes no practical difference (has no effect on the outcome of any experiment), and thus basically there's no reason to care? Doesn't it matter to someone, if for example we say "This supernova we're just seeing now occurred a million years ago" vs "It occurred just now." Doesn't a simultaneity convention greatly affect the interpretation of quantum mechanics?

That's why you define "simultaneity". (Once you have that you can set the time of clocks at each of the locations. They can be synchronized if they're at relative rest.) Whether you use the standard definition of simultaneity in SR, or some alternative, you can still measure the apparent delay for any given observer, between when it observes an event occurring coincident with the signal being sent, and an event coincident with the signal being received. SR lets you predict these things for a given inertial observer by considering both relativity of simultaneity and delay of light. However, I'm trying to argue that by using the alternative "apparent simultaneity", delay of light can be treated as relativity of simultaneity (meaning that the receiver of a signal can treat the transmission and reception as apparently simultaneous, but the two events are not apparently simultaneous for other observers in general).

Has anyone else (historically) proposed a unification of relative simultaneity and measurable delay of light? Wouldn't such a model be a valuable simplification, if it was consistent with SR? What I mean by this is: Depending on observer viewpoint, a delay of light between a transmission event and a reception event appears to be somewhere between 0 seconds to 2d/c inclusive. A receiver of light sees transmission and reception appearing simultaneous, a transmitter sees it take 2d/c, and an observer equidistant to transmitter and receiver sees it appear to take a time of d/c. It is possible with an alternative simultaneity (based on appearance of simultaneity) to treat these observed apparent delays of light as relativity of simultaneity. Is there anything valuable in that? Would it be more important to prove that this model is consistent with the observables of SR, or would it also have to be shown that there is a practical benefit to such a model?

I would add that this is true only relatively, not in any absolute way. Local time is experienced at the normal rate, and the time of moving objects (or usually equivalently: objects that you are moving relative to) is relatively slowed while moving inertially. More details would probably require a deeper discussion of relativity and deciding what it means to experience the time of a clock other than a local one.

Uh oops I was off by a bit, only a factor of a thousand. Those supercaps max out around 2000 amps! So probably 50 or fewer for a AA battery would exceed reaction time. Probably 1 supercap would suffice for a small button cell.

http://electronics.howstuffworks.com/capacitor2.htm says that an AA battery holds about 2.8aH, and would need a 10080 F capacitor. Three of the biggest of these http://www.maxwell.com/products/ultracapacitors/products/k2-series should do it. However, 2.8aH is 10080 amps per second for 1 second, and those supercaps max out around 2 amps. So you'd need 5000 of them for 1 sec discharge? Or maybe 50000 to exceed human reaction time. There are probably more suitable high-amp capacitors. Another thing to think about: Livermore's Petawatt laser maxed out at 680 joules for a trillionth of a second https://www.llnl.gov/str/MPerry.html and an alkaline AA battery holds about 9000 joules. You'd need 10x the capacity but about a 10 billionth of the wattage.

Probably, but I doubt it would be a battery afterwards. Even if you short it, it will still take some time to discharge, and will probably damage the battery. See http://www.electro-tech-online.com/threads/shorted-battery-what-happens.128024/ for some interesting related comments. If you destroy the battery you can probably remove its stored energy. Say you vaporize the battery with enough energy, you might make it impossible to get any electrical energy out of it (as long as you don't include added heat etc as part of its "stored energy").

From OP's link: Perhaps one must experience it to understand it. At least in part this comes from the "urgent need" to get your ideas across, and the urgency makes investing time in learning seem like a diversion. I think that the less understanding one has of the fundamentals, the more daunting it is to consider learning them, and the bigger a wall standing in the way of getting your idea across it seems (paradoxically). There is also a common desire to avoid "tainting" ones original ideas with everyone else's (ie. learning the fundamentals). This isn't as silly as it sounds, because certainly everyone has ideas that we don't bother to explore once we learn what other people have done along the same lines. Most ideas born of ignorance are worse than what's already been done (say 99.999% to borrow a number from the link). Yet, while science progresses iteratively it can sometimes end up in "local maximums", from which we might progress only with a radical change. Neither of these convictions make an amateur hopeless because there's a way out. You can try to get your idea out without learning, and you can explore your idea on your own as far as you can go, and when that doesn't work out, the relative cost of learning the fundamentals becomes lower. Either you can dedicate your life and life's savings to promoting your idea with websites etc, or you can take your "fully developed idea" and start seeing how it fits into the mainstream without worrying about tainting it. At that point, a life-long avoidance of learning more physics and maths should seem like a more daunting waste of time. If the idea's really good, it will survive being shaped and honed by existing physics. Defending that potential 1 in 100000 is exhausting because of the other 99999 who more often ruin it, but still we can't generalize to 100% and ignore the exceptions. Even statements like "If it has no math it's pseudoscience" aren't true in 100% of cases. These discussions seem to attract an anti-crackpot flavor of pseudoscience that goes mostly unacknowledged. As Stephen writes in the link, "If your theory has no mathematics, I'm sorry to tell you that I'm 99.999% certain it's pseudoscientific waffle." I think that he deals with this in the right way, which seems to be that it is simply not worth it for an individual to bother with your idea with those odds. But he's not saying that your idea is certainly worthless or that 100% of such "theories" can safely be suppressed.

It is not made any clearer. Also I get confused here: What do you mean by that the speed of light measured by a distant observer approaches zero? Doesn't the speed of light remain c, and only the coordinate speed of light approach zero?

It is clear that this is what's been discussed all along. It's been pointed out several times (including by you) that it's coordinate speed of light that is being discussed. If it's confusing or bothersome perhaps everyone could repeat "coordinate speed" every time it's used. I'm curious about your correction. What is the difference between speed in Schwarzschild coordinates and coordinate speed in Schwarzschild coordinates?

What is proper speed?

I think that is fine because mathematically there is an equivalent... Continuous acceleration can be handled with integration of infinitesimal instantaneous accelerations. Mathematically, instantaneous acceleration must be acceptable at some level, even if it is also infinitesimal. We still have to be careful not to describe physically impossible situations, but abstractly this is okay, if we don't require any absolute physical instantaneity but are simply speaking of infinitesimal or negligible times, and we can set it up so that arbitrarily large durations can be ignored! ... if we're careful. d_rest = 100 v = 0.6 gamma = 1.25 Q1: d = d_rest/gamma = 80, the ground frame's length of the ship. tBert' = 60, coordinate time at Bert, using Lorentz transformation with t=0, x=-80 You can also figure it out by figuring out how long it takes the ship to pass the ground observer in the different frames. How would you figure this out? Q2: They both accelerate at respective proper time 0, so Bert accelerates first (60 units ago in Frank's frame). Q3: 60*gamma = 75 Q3b: The original ground distance was 80. Bert has closed that distance at a rate of 0.8 - 0.6 = 0.2 in ground frame, for a time of 75, = 15. The new distance at time 0 is 65. Q4: Frank accelerates at Frank-time 0. Bert accelerated 60 Frank-units ago, which is a time of 75 in ground frame, which is a Bert time of 45. Is this what you've got, so far? Sorry, I'm getting sloppier as I go.

Thanks for trying. The idea is simple but proving correspondence with SR is complicated. It could probably be done much simpler.

Your challenge is off topic! Fine, I retract my statement that relativity of simultaneity is experimentally confirmed. Is it enough to state that relativity of simultaneity is a theoretical consequence of SR? Would you accept that? Do you have a suggestion for a peer review journal that would be appropriate to submit this to?

I am quoting from the paper that I cited. It is written by Einstein. I quote the defining assumption upon which his definitions of time, simultaneous, and synchronous are built. You can use SR consistently without understanding the assumptions used to define it. I am examining one of those assumptions. You're mixing your terms. Relativity of simultaneity is confirmed by experiment. Edit: No particular definition of simultaneity is confirmed, but it is confirmed that absolute simultaneity of events is not physically possible. Anyway I don't argue in favour of conventionality of simultaneity. It is irrelevant for my paper; standard simultaneity is uniquely defined whether or not it is conventional, and apparent simultaneity is unique whether or not it is conventional. I see no point in considering both relativity of simultaneity and conventionality of simultaneity separately. This point is addressed in the paper. Relativity is essential. Conventionality is not.

Relativity of simultaneity is the concept that observers in different reference frames generally measure a different simultaneity of events. That is not at all what I'm speaking of here. In SR, for a given inertial observer, there is a definite simultaneity of events. For observer O in an inertial reference frame, two events are either simultaneous or not. Einstein provided a definition that determines whether two separate events are simultaneous. This definition can be used to define Einstein synchronization of clocks. However, the definition of simultaneity applies whether it's used to set clocks or not. You can say for certain in SR whether two events are simultaneous for a given inertial observer using Einstein's definition, without needing to synchronize any clocks. Other people have argued that Einstein's definition of simultaneity is not unique. This is usually debated as "conventionality of simultaneity". Some people (Reichenbach and Grünbaum notably) have argued that simultaneity is conventional, and often involving a different speed of light on each leg of a return trip of light. Other people argue that simultaneity is unique, and usually base this argument on a set of "reasonable" assumptions, which usually involve Einstein's assumption of equal timing of both legs of a return trip. It doesn't really matter I think, because the whole conventionality argument turns out to be pointless with respect to the contents of my paper. Einstein's definition is the simplest and most useful that I've found. What I'm describing in the intro is "standard simultaneity". The term is used in the following places: Uniqueness of Simultaneity, Domenico Giulini. http://arxiv.org/abs/gr-qc/0011050 Conventionality of Simultaneity, http://plato.stanford.edu/entries/spacetime-convensimul/ Apparent Simultaneity, Ben-Yami, Hanoch, http://philsci-archive.pitt.edu/3260/ Even if "standard simultaneity" is not a common enough phrase, I explained what it means. The concept of simultaneity is clear in SR. I don't think I have to explain it all. Einstein states that an assumption is required. He establishes by definition that the time required by light to travel from A to B is equal to the time required for it to travel from B to A. These statements are true! Given the other postulates and assumptions of SR, standard simultaneity as I've described it is a sufficient and a necessary assumption to uniquely define simultaneity per inertial frame. I've left out the rest of the details of SR from the first paragraph of the intro. If you read past it, you'll see that all of the relevant details and assumptions that I need are stated.

No, I was talking about a uniform gravitational field. Anyway I might be wrong... Is gravitational redshift associated with a change in gravitational potential, or with change in gravitational field? I think it must be the former, because it's related to conservation of energy? But the wikipedia page http://en.wikipedia.org/wiki/Gravitational_redshift begins with: "... electromagnetic radiation originating from a source that is in a gravitational field is reduced in frequency, or redshifted, when observed in a region of a weaker gravitational field." It also says "frequency of the electromagnetic radiation is reduced in an area of a higher gravitational potential (i.e., equivalently, of lower gravitational field)", and I don't think these are equivalent in a uniform gravitational field, so they must be assuming a gravitational mass and non-uniform field?