Lorentz Jr

Wait, so now you're disagreeing with the Wikipedia links you just posted to explain proper time and coordinate time? Is that your new position? And you're also claiming authority to define those terms yourself? In general relativity, all free-falling frames are physically indistinguishable from rest frames. Every time you make an excuse for your mistakes, you provide more evidence of your ignorance. More ignorant fantasies. Proper time is always the time along a world line, the time experienced by a moving object. The inertial observer's frame is the rest frame. Okay, so again, you know the word "invariant", but you don't know what it means. Coordinate time is time in the observer's frame by definition. It's not true "because the coordinate time is not invariant.." Yes, I got that you're still trolling, you're still making stuff up and refusing to admit that you were wrong. What does "the only reference frame" mean? Why don't you summarize it for me. If you're such an expert, what does that article say, in your own words?

Still waiting..... Proper time: That's inside the car, where the engine clock is. Traveling along its world line as it accelerates. Coordinate time: That's the ground, buddy. The observer is on the ground. "Each engine clock will be in coordinate time" is 100 percent, Grade-A baloney. B-A-L-O-N-E-Y. Baloney.

Argument from authority I've seen the label, but your comments still don't make sense to me, and I've met way too many trolls on the internet to trust labels. Sorry, but that's more meaningless nonsense. When an object moves relative to an observer, "coordinate time" refers to time in the observer's frame and "proper time" refers to time in the object's frame. This thread is about accelerating a train relative to the ground, so time in the ground's frame is the coordinate time for the problem and time in each car's frame is the proper time for that car. Again, you're throwing around terms like "line element" without knowing what they mean. There are lots of line elements for lots of different objects. The line element of the car's motion is exactly what the clock in the car follows, so each engine clock in a car will measure that car's proper time, not the ground's coordinate time. Blah blah blah blah blah blah blah blah blah blah blah blah. You're using words to intimidate, not to communicate. You're using them incorrectly, and you're not saying anything with them. "Each engine clock will be in coordinate time" is 100 percent, Grade-A baloney.

I hadn't quite understood his plan at that point. I thought he wanted to accelerate the cars equally in the ground frame, and I was pointing out that they need to be closer together once they're moving. So their accelerations need to be different functions of time. Maybe not. I was just pointing out that, even taking only special relativity into account, if events along the length of a moving train are simultaneous in the ground frame, the ones at the front happen before the ones at the back in the train's frame, so the cars would be pulled apart if they accelerate equally in the ground frame. md65536. Really? Based on what? How else would one accelerate train cars without stress between them, and what do you think makes synchronized self-propulsion impossible? Then why did you say "This is another way of putting what I said earlier" in response to this comment: .. and then point out that no one had explicitly answered the comment, if it's not at issue? Ladders don't normally fly through barns at relativistic speeds either, but they make for good exercises. I think Dima just wanted to accelerate the train quickly without introducing internal stresses. I don't think his post had anything to do in particular with any specific observers.

I am familiar with GR terminology, and I'm also familiar with trolling tactics. Like intentionally misreading comments, for instance. What in the world does "Each engine clock will be in coordinate time" mean? What does it mean for a clock on a moving train car to "be in coordinate time"? @studiot? Do you understand that? Because I'm not getting anything that makes sense to me from this other guy, except as ignorant trolling.

What in the world is this supposed to mean? It sounds like more nonsense.

This entire thread is about the rigid-rod problem. That's the whole point of the OP's formula. The fact that you introduced the term "rigid rod" and name-dropped Born doesn't mean you said anything new. If I understood correctly, the OP's goal was to accelerate each section of the "rod" as needed to minimize the stresses between them.

So he wasn't very coherent. This is the internet, not Princeton or Cal Tech. 😄 You mean a long chain of many smaller objects. That post was to a different person and about a different subject. I was commenting on MD's suggestion of instantaneous acceleration to the target speed. I've been assuming the lengths of the cars are neither especially long nor especially short. In order for them to all accelerate simultaneously without getting pulled apart or crashing together, the information about their accelerations as a function of time has to be contained in each car from the start, and all the engines have to start accelerating at the same time. I don't see how. The OP's goal was for the cars to all accelerate simultaneously, and Mordred pointed out the obvious fact that doing so isn't possible if the accelerations have to be controlled externally. After I had already addressed the issue, although not explicitly, because I thought the OP had made it clear that he was at least trying to deal with that problem. Patience. We'll get there. 🙂

What we're stuck with is needing to stick to the subject of the thread and read other people's posts more carefully.

I have no idea. I was just addressing the OP's idea of accelerating the cars together.

The point of what? The OP didn't say a word about turning. No one except you said anything about turning. You talk about signals that nobody mentioned; you talk about turning, which nobody mentioned; every time someone proves you wrong, you change the subject and talk like that's what we were discussing all along. PS: It's "you're", not "your". Your English is almost as bad as your physics.

We're not changing anything, my friend. The OP said the engines don't interact. That requires a setup along the lines of what I described, to keep the engines synchronized without real-time signals between them. So I have no idea which goalposts you think we might be changing. Also, the OP mentioned a long train, not long cars. Rigidity isn't a serious issue for short cars with flexible couplings. What do you think the OP's original intention was? He presented a scheme for accelerating all the cars of a lengthy train together, and in another post he explicitly said it would need to be done without signals being sent between cars. I addressed that implicitly in my second post. In order to keep the cars all spaced properly as they get length-contracted, the rear cars have to initially accelerate faster than the forward cars, and then the forward cars have to speed up later as the rear cars catch up to them.

What signal? Who said anything about a signal? Other than you, of course. An array of starter switches can be positioned, one near each car of the train, connected to synchronized timers, so they're all timed to start the engines simultaneously in the ground frame. Then the pre-programmed engines can accelerate their cars, each according to its own previously calculated schedule, with no further input. As I already mentioned, it's probably a silly and even dangerous thing to do in real life, and I don't think DimaMazin's timing function would work correctly. But there are no signals involved after the initial setting of the timers, so your comments about signals are immaterial.

Enough to know that "Proper time would follow the wordline between engines" is meaningless gibberish. Which world line? One can construct an infinite number of world lines, and the ones that are relevant to individual cars don't extend "between engines". Sure, buddy. Whatever you say. 🙂

Each car stretches out separately. If two adjacent cars get longer, the car in front has to move forward or the rear one has to move back. Then you run into the problem of propagating the acceleration itself through the length of the car. As studiot said, you have to analyze relativity problems in terms of point events. What happens to extended objects tends to be complicated. I'm sorry, but that's just nonsense. First of all, it's "world", not "word"; and second, the world line for any one (small) object doesn't follow anything except that object. It's theoretically possible to calculate the accelerations of individual cars as a function of time that will keep the cars lined up correctly (and then convert the accelerations to functions of the cars' proper times), and it's theoretically possible to program an engine to provide the calculated acceleration for that car independently of other cars and engines (and it's easy enough to synchronize multiple starter switches when the train is motionless). So there's no problem at all in principle. The only possible problem would be that it's probably dangerous and impractical, so no one in their right mind would actually do it unless they prepared the train and cleared its surroundings very carefully. 😄

Unless you calculate the acceleration required for each car as a function of its proper time before starting and pre-program it into the engine. Then start the engines from a standstill using synchronized triggers. 🙂

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It will start out contracted and then get squished halfway through because it loses its contraction. That's what I meant by complications. Accelerating all at once is just the limit of accelerating quickly. It doesn't mean nothing happens in between. Except each car will crash into the one in front of it because the car in front isn't contracted yet.

When the theory of electromagnetism was first developed, it was formulated in terms of two fields. Charged particles contribute to the electric field, and magnets contribute to the magnetic field. The fields also interact with each other and with moving charges and magnets. The current thinking is that the electric field and the magnetic field aren't really separate fields, because they look different to different observers (moving at different velocities). They're treated as aspects of a single, more complicated field that determines how light works, and it's called the electromagnetic field.

It means changing periodically, going up and down like a bouncing ball or a vibrating string. Electric and magnetic fields are theoretical explanations of why magnets and charged particles exert forces on each other. Photons are both electric and magnetic. Nobody knows exactly why fields are quantized, but experimental evidence has shown that they are, and a photon is defined as one quantum of the electromagnetic field.

Accelerating all of the cars in a train instantly in the ground's reference frame would result in a chain of length-contracted cars separated by "uncontracted" distances. The couplings between the cars would all break. But that's not the ground frame. There are also complications between -u and +u, so the couplings would have to be flexible. Either that or each car would have to be pre-programmed with its own specific acceleration schedule. In the ground frame, the back end of the train has to initially accelerate more quickly than the front end, because the distances between the cars need to shrink along with the cars' lengths.

Once the cars start moving, their accelerations won't be simultaneous in their reference frame anymore. The front cars will be accelerating earlier than the rear cars, so the cars will be pulled away from each other.

Without relativity, the Schrödinger equation obviously suggests the existence of waves. Non-realist interpretations give up determinism in favor of relativity and classical ontology, but particle-based attempts at quantizing gravity haven't been working very well (hence my signature 😊). Roger Penrose has been taking the opposite approach, of "gravitizing" quantum mechanics, as he puts it.

I blame Einstein (hence my username). The two main reasons people believe in particles are (1) they're an extrapolation of classical "objects" to small sizes, and (2) objective collapse of wave-functions has to be superluminal. Another link: Diósi–Penrose model

Woit reaction #2 (full blog post): The Wormhole Publicity Stunt For context, there's a youtube video by Quanta Magazine, featuring Leonard Susskind: How Physicists Created a Holographic Wormhole in a Quantum Computer