Why in the world would Einstein suggest....

@Thomas,

Quote:

...[it is] equally valid to ask "will this train stop in Chicago?".

Again, no it is not. Not for the guy on the uniformly-moving train. Not in the context of the theory of special relativity, which MANDATES that he consider himself to be at rest.

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@layman,

layman wrote:

The guy on the train must consider himself to be MOTIONLESS for the math to work out in a way that is consistent with Einstein's postulates.

Not must, but can. And you have not demonstrated that Einstein said anything that amounts to must. You have just repeatedly told us so, which is not the same.

1 Reply

@Thomas,

Quote:

You have just repeatedly told us so, which is not the same.

I didn't say so, really. The respected physicists I have quoted say so. And anyone familiar with the mathematical protocols of SR would know this.

Have you actually read the thread, Thomas?

SR can ONLY work if A and B, two relatively moving observers, each claims that HE is at rest and the other guy is the one "moving." Without that built-in assertion of those two contradictory and mutually-exclusive "contentions" by different observers, the theory falls apart.

I have quoted Dr. Morin, a Harvard professor of physics, as an "authority" who says this.

This requirement is imposed by the notion of the "relativity of simultaneity."

1 Reply

@layman,

layman wrote:

Quote:
You have just repeatedly told us so, which is not the same.

I didn't say so, really. The respected physicists I have quoted say so.

Respected or not, quoting a physicist as saying that Einstein said something does not amount to a demonstration of Einstein actually saying it. If what you're claiming is really so obvious, you shouldn't have any trouble finding an actual Einstein quote backing you up.

layman wrote:

Have you actually read the thread, Thomas?

I have, in an unsuccessful chase for your elusive demonstration. In the process, I have learned that Brandon9000 made pretty much the same points that I was going to make. Maybe I should have known I wouldn't get through to you past your "authority"-based assertions when Brandon didn't.

1 Reply

@Thomas,

Forget authority, then, Thomas. If you want to reject Harvard physics professors, so be it. Let's reason this out together. Is there anything we can agree on?

Do you agree that, in SR, it is the moving clock which runs slow? I have quoted Einstein on this topic.

As an aside, I use "Einstein" somewhat loosely to refer to SR as it is interpreted and employed by physics today. I am talking about the theory, not Al's specific words.

That said, Einstein has indeed written, somewhat extensively, on the topic. I was referring to his example in the OP. It was the example where he explained the "relativity of simultaneity." I could find that, and cite it, or refer you to it, but my point is not about his particular words he said to begin with. I am not asking a historical question about the precise words he might have used. I am talking about his theory, and its implications. He did not always completely spell out all the implications of his theory, unfortunately.

Again, forget what he said. Let's reason this out.

1 Reply

@layman,

layman wrote:

Do you agree that, in SR, it is the moving clock which runs slow? I have quoted Einstein on this topic.

I agree, as long as we keep in mind that observers in different inertial systems will have different views on which clock "the" moving one is. If two observers, O1 and O2, fly by each other at a constant relative speed somewhere close enough to c, and each holds up an alarm clock for the other to look at, each will come away with the impression that the other observer's clock runs slower than her own.

layman wrote:

Einstein has indeed written, somewhat extensively, on the topic. I was referring to his example in the OP. It was the example where he explained the "relativity of simultaneity." I could find that, and cite it, or refer you to it,

(1) Apparently not, or else you would have done it already. At the very least, you're finding the task materially harder than coming up with excuse after excuse for not backing up what you said. But I'll let this one pass because I agree that the "simultaneity" of events at different locations does depend on the frame of reference.

(2) While it is true that simultaneity is relative, it's irrelevant to your original post. If it was indeed absurd to suppose that Chicago is moving relative to the train --- and it is not absurd --- that wouldn't just make nonsense of the Lorentz Transformation. It would make nonsense of the Galileo Transformation too.

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@Thomas,

Quote:

I agree, as long as we keep in mind...each will come away with the impression that the other observer's clock runs slower than her own.

Ok, good, I agree with what you said, too. Now, do you agree that saying this: "each will come away with the impression that the other observer's clock runs slower than her own" is tantamount to saying this: "each will come away with the impression that the other observer is moving, while he is not?"

Btw, I don't think the phrase "will come away with the impression" captures the situation, but I will leave that aside for now.

1 Reply

@Thomas,

Quote:

that wouldn't just make nonsense of the Lorentz Transformation. It would make nonsense of the Galileo Transformation too.

An interesting claim, and one which I would like to discuss with you further, but for now I'm just trying to take one thing at a time.

1 Reply

@layman,

layman wrote:

Now, do you agree that saying this: "each will come away with the impression that the other observer's clock runs slower than her own" is tantamount to saying this: "each will come away with the impression that the other observer is moving, while he is not?"

No, it's not tantamount to saying that. The two points are distinct. Galileo would have agreed with the latter but not the former.

layman wrote:

Btw, I don't think the phrase "will come away with the impression" captures the situation,

No it doesn't. In both cases it's an objective, predictable, and reproducible measurement. It isn't just a subjective impression.

layman wrote:

but I will leave that aside for now.

Good idea. Let's leave it aside.

1 Reply

@layman,

layman wrote:

An interesting claim, and one which I would like to discuss with you further, but for now I'm just trying to take one thing at a time.

In that case, I think you're taking things in the wrong order. You can't run before you can walk. And you can't understand the Lorentz transformation and its connection with the special theory of relativity before you understand the Galilean transformation (which treats positions and speeds as relative but time as absolute). You clearly don't understand the implications of the Galilean transformation, so I suggest you study it first.

1 Reply

@Thomas,

Quote:

No, it's not tantamount to saying that. The two points are distinct

Yes, I agree that the two points are, in a technical sense, distinct. And yet they are unseparately concomitant, aren't they?

Is their something in what either one of these physicists say that you think is mistaken?

Quote:

A commonly heard phrase in the realm of special relativity is "Moving clocks run slowly". But—even in the context of special relativity—is it always true? The answer is no. It's only true when a clock's ageing is measured in an inertial frame

http://math.ucr.edu/home/baez/physics/Relativity/SR/movingClocks.html

Quote:

It is important to realize that it really is the case that each of these people measures the other's clock as running slowly. So who is really running slowly? So long as both remain within their fixed inertial reference frames, the answer is relative and always the other guy.

http://www.astro.virginia.edu/~jh8h/Foundations/quest7.html (emphasis is original, not mine)

1 Reply

@Thomas,

Quote:

the Galilean transformation (which treats positions and speeds as relative but time as absolute).

I understand that, and I agree.

Quote:

You clearly don't understand the implications of the Galilean transformation,

What "implications" do I not understand? I certainly realize that, having "discovered" that relative speed affects the rate at which clocks tick, one cannot use Galileo's transformations unaltered.

But what does this have to do with your statement that:

Quote:

If it was indeed absurd to suppose that Chicago is moving relative to the train.... It would make nonsense of the Galileo Transformation...

Galileo quite adeptly made his point about how physical experiments would turn out in a closed cabin of a relatively moving ship. But he did not claim that it was "impossible to know who's moving," if that's what you are suggesting.

In fact, he said that once one got "on deck" one could easily to determine that the ship was moving, because one would see that he was moving relative to fixed points on the coast. This is, after all, the same guy who was persecuted for claiming that the earth was "actually moving" around the sun.

1 Reply

@layman,

layman wrote:

Yes, I agree that the two points are, in a technical sense, distinct. And yet they are unseparately concomitant, aren't they?

No they aren't. As I just told you, Galileo would have agreed that each observer would observe the other to be the moving one, but disagreed that each observer would observe the other one's clock to be the slower one. Galileo would have claimed the observer would see each other's clocks running at the same speed. The to points do emphatically not follow from one another.

Now let me turn to your quotes.

Quote:

A commonly heard phrase in the realm of special relativity is "Moving clocks run slowly". But—even in the context of special relativity—is it always true? The answer is no. It's only true when a clock's ageing is measured in an inertial frame

I agree with that. Once you have acceleration, the symmetry breaks, and the accelerated clock ends up running slower, even according to its own frame of reference. You can't get effects like the twin paradox without acceleration (or gravity, which amounts to the same according to the general theory of relativity). On to the next quote

Quote:

It is important to realize that it really is the case that each of these people measures the other's clock as running slowly. So who is really running slowly? So long as both remain within their fixed inertial reference frames, the answer is relative and always the other guy.

I agree with that, too. May I ask where you're going with this?

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@Thomas,

Quote:

I agree with that, too. May I ask where you're going with this?

Sure. Both of these sources say that every observer always sees the other's clock as going slow. Yet you said it was quite appropriate for one observer to take the position that it was indeed his clock that was running slower, and that the other guy's was running faster (which he would have to do if he conceded that it was he, rather than the "other guy," who was actually moving).

Do you disagree with what this physicist says?

Quote:

One might view the statement, "A sees B's clock running slow, and also B sees A's clock running slow," as somewhat unsettling. But in fact, it would be a complete disaster for the theory if A and B viewed each other in different ways. A critical fact in the theory of relativity is that A sees B in exactly the same way that B sees A.

http://www.people.fas.harvard.edu/~djmorin/chap11.pdf (Page XI-14)

1 Reply

@layman,

layman wrote:

What "implications" do I not understand?

You don't understand that the Galilean transformation alone is enough to justify the statement, "me and my train are resting; it is the city of Chicago that is moving towards me at a constant speed."

layman wrote:

Galileo quite adeptly made his point about how physical experiments would turn out in a closed cabin of a relatively moving ship. But he did not claim that it was "impossible to know who's moving," if that's what you are suggesting.

Granted, I don't know enough about the history of science to know what the person Galileo Galilei said about the matter. But yes, his transformation does yield this claim when you apply it to Newton's laws of motion.

Suppose the observer on Galileo's ship looks at a physical experiment on the beach. She will measure different positions and different velocities than an observer on the beach would, because positions and velocities are relative to their respective frames of reference. But the relations between the positions and speeds, as predicted by physical laws like the conservation of momentum, the conversation of energy, and so forth, will be the same in both systems. Hence, as long as neither the ship nor the beach accelerates, it is indeed impossible to look at the outcome of any physical experiments and deduce which observer is 'truly' the moving one.

1 Reply

@Thomas,

Quote:

Hence, as long as neither the ship nor the beach accelerates, it is indeed impossible to look at the outcome of any physical experiments and deduce which observer is the moving one.

Ok, fine, I agree. But what if someone looks at something other than just physical experiments? Suppose both notice that there is a strong wind. Suppose both notice that the ship's sail are fully billowed. Now what? Wouldn't they agree that it is the ship moving relative to the shore, rather than the shore moving, relative to the ship?

1 Reply

@layman,

layman wrote:

Sure. Both of these sources say that every observer always sees the other's clock as going slow. Yet you said it was quite appropriate for one observer to take the position that it was indeed his clock that was running slower, and that the other guy's was running faster (which he would have to do if he conceded that it was he, rather than the "other guy," who was actually moving).

Not actually moving, actually accelerating. And both observers would agree which one that was.

Quote:

One might view the statement, "A sees B's clock running slow, and also B sees A's clock running slow," as somewhat unsettling. But in fact, it would be a complete disaster for the theory if A and B viewed each other in different ways. A critical fact in the theory of relativity is that A sees B in exactly the same way that B sees A.

I have no problem with that.

2 Replies

@Thomas,

You said you agreed with this:

Quote:

...the answer is relative and always the other guy.

Yet, when I pointed out that's it's rather self-contradictory to say BOTH that:

1."the answer is relative" AND that it is
2."always the other guy"

You merely responded by saying (in effect) that it's not "always the other guy." I didn't see you cite any source for that claim. Do you have one?

0 Replies

@layman,

layman wrote:

Ok, fine, I agree. But what if someone looks at something other than just physical experiments?

Everything is a physical experiment, including wind blowing into the ship's sails.

layman wrote:

Wouldn't they agree that it is the ship moving relative to the shore, rather than the shore moving, relative to the ship?

No. They would agree that the wind applies equal force to the ship as to the beach --- assuming, for the sake of the argument, that there's a sail attached to the beach. They would agree that the beach, and the planet attached to it, have a mass that dwarfs the mass of the ship. Consequently, they would agree that the wind can materially accelerate the ship, but not the Earth. Your hypothetical is about acceleration and mass, not just movement.

1 Reply

@Thomas,

Quote:

Not actually moving, actually accelerating.

I think you might have misread it, Thomas. He was talking about how inertial (not accelerating) frames always see the other clock running slow.

This is NOT true, when one is accelerating, of course. Because even SR concedes that accelerating motion is ABSOLUTE motion.

1 Reply

Why in the world would Einstein suggest....

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