Why in the world would Einstein suggest....

@layman,

Actually it does because the entire quote shows he never says that CMB is motionless but is only a frame of reference that they can use as motionless just like any other frame.

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@dalehileman,

Quote:

"Whether they are moving with respect to, for example, the Sun, doesn't enter into the question"

I don't recall even having mentioned the Sun and have no idea how it could enter into the discussion. Unless you mean for it to represent that arbitrary "stationary" ref; but I don't see how that makes any more sense than my version.

Dale, I just said "sun, for example." My only point then, and now, is that we are not even talking about an issue involving "absolute motion." Brandon keeps acting like that IS the question, but it isn't.

Whether or not the train (or the earth, for that matter) is moving with respect to some absolutely stationary object, or with respect to ANY other object, is NOT the question. The question is about which is moving relative to the other. Changing the question might well change the answer, but, as you say, that's just a case of misinterpretation, it seems.

1 Reply

@parados,

Quote:

Actually it does because the entire quote shows he never says that CMB is motionless but is only a frame of reference that they can use as motionless just like any other frame.

He says what he says, to wit:

Quote:

There clearly is a frame where the CMB is at rest, and so this is, in some sense, the rest frame of the Universe

.

He is talking about what he calls the "rest frame of the universe."

He says that THE PHYSICS don't change in other frames, that's all.

1 Reply

@parados,

Quote:

Actually it does because the entire quote shows he never says that CMB is motionless but is only a frame of reference that they can use as motionless just like any other frame.

I'm not a physicist, Parados, but, from what I understand, this whole CMB thing is not just a matter of arbitrarily deciding to "use" the CMB as a rest frame.

Why not?

Because, they say, as a physical matter, it is ONLY in the CMB frame (or any other frame which is at rest with respect to the CMB) that the speed of light will appear constant, regardless of the direction it is coming from.

Of course, that is also what any ether theory says. Such theories say it will only be in the ether frame that the speed of light is constant. In all other frames it will "appear" to be constant (i.e., it will be measured to be constant) but that is only because of the distorting effects of time dilation and length contraction.

In the case of the CMB, any body that is moving with respect to the CMB will also see opposing Doppler shifts (indicating a speed differential). The doppler shift will "tell" you that everything you see when looking in one direction is moving away from you, while everything you see when looking in the opposite direction is moving toward you.

The only conclusion is that you are in fact moving away from one "side" and toward the other "side."

But, in the frame of the CMB, no such Doppler shifts will be seen.

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@layman,

Quote:

There clearly is a frame where the CMB is at rest, and so this is, in some sense, the rest frame of the Universe

I guess if you completely ignore part of his statement you could make your claim.

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@layman,

Quote:

Because, they say, as a physical matter, it is ONLY in the CMB frame (or any other frame which is at rest with respect to the CMB) that the speed of light will appear constant, regardless of the direction it is coming from.

Wow. You really don't understand physics do you? The speed of light is constant in every frame of reference and constant from every direction.

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@layman,

I said:

Quote:

The doppler shift will "tell" you that everything you see when looking in one direction is moving away from you, while everything you see when looking in the opposite direction is moving toward you.

That was an inaccurate and sloppy way of expressing it.

It is the CMB itself, which has been shown to be homogenous, which will appear to be moving away from you if looking in one direction, and which will appear to be moving toward you when looking in the opposite direction (not "everything," as I said in the initial post).

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@parados,

Quote:

Wow. You really don't understand physics do you? The speed of light is constant in every frame of reference and constant from every direction.

Heh, Parados. You really don't understand what the effect of a motionless, preferred frame, combined with time and length distortions is, do you?

That, my friend, is "physics" and physical theory.

1 Reply

@layman,

Einstein postulated that the speed of light is constant in every frame of reference. It was postulated (as he himself emphasized), not proven. Once you ASSUME, that, certain consequences would follow. But you cannot rely on your subsequent deductions to prove your assumption.

Other theories of motion postulate otherwise, and are just as effective in making predictions as SR. There is no known way to experimentally show which one (of many) is correct.

As I said before, any experiment which is deemed to "confirm" SR, also confirms a neo-lorentzian theory of motion which posits absolute (rather than relative) simultaneity.

1 Reply

@parados,

Quote:

The speed of light is constant in every frame of reference and constant from every direction.

Therefore, when you assert this as an undisputed fact, you merely display your ignorance of the way physical theories actually work. It shows an unfamiliarity with the foundations of the theory, as opposed to the consequences you might deduce from a given theory.

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@layman,

Quote:

The question is about which is moving relative to the other

Sorry Lay but still can't make sense of it

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@dalehileman,

Dale, I don't know if my last post made any sense to you, but it bothers me that we may be misunderstanding each other. You seem to be the only (or at least one of the only) participant(s) who seems to have an open mind and who poses questions and raises issues to discuss rather than just making unqualified assertions by fiat.

If I understood your point originally, it was basically was that one could hypothesize a frame a reference (and there would be such a frame of reference) from which it would appear that the train is motionless and the earth is moving. I agree that this is quite possible.

But I can't see where the question about how the train might appear to some third frame is relevant to the question I posed.

Let's say you are six feet tall and weigh two hundreds pounds, and I say so. Someone could then say that, if viewed from the top of the Sears Tower while lying on the sidewalk below, you would appear to be the size of an ant. Then what?

I would say, sure, I agree he could "appear" that way from some different optical perspective, but that doesn't mean he "is" (or "could be") the size of an ant.

1 Reply

@layman,

To continue, Dale, I don't think it changes anything if you say that the frame from which the train is viewed as motionless is, itself, "absolutely" motionless.

Even if that were the case, and could be proven to be so, it wouldn't change anything.

The earth and the train would still be moving relative to each other, and the train would still be the one moving relative to the earth, even if it were motionless in some "absolute" sense.

That's because the question is not one of "absolute motion." The question really just boils down to this: Which one accelerated? One could also ask "which one requires a continuous input of energy to maintain its current state of motion?"

Assuming that, before it left the station, the train was moving at the rate of 60 mph relative to some preferred frame, the fact would remain that it had to accelerate to achieve the status of being "absolutely motionless." As between the train and the earth, it was the train which had to change it's state of motion.

1 Reply

@dalehileman,

Quote:

Sorry Lay but still can't make sense of it

Dale, I was composing the two posts which follow yours while you were posting this one, it seems. That's why I said that I "didn't know" if my prior post made sense to you.

I now know: It didn't.

Do those following posts help any?

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@layman,

To elaborate a little more: I said:

Quote:

The question really just boils down to this: Which one accelerated? One could also ask "which one requires a continuous input of energy to maintain its current state of motion?"

Take another case where a buoy, floating on the ocean's surface, and a "steamship," cruising at 30 knots, "pass each other."

Could anyone persuasively argue that you can't tell which one is moving, because each is maintaining a uniform speed?

I don't think so. Their respective "uniform speeds" may be reciprocal, but they are not otherwise identical. It is the steamship, and only the steamship, which requires continuous power to move at 30 knots. The buoy requires no such input.

Of course I would say that, for that reason alone, the ship is not in a state of "inertial motion". But Al seems to ignore this when he produces the "explanation" of relative simultaneity involving a passenger on a train.

1 Reply

@dalehileman,

I also said:

Quote:

The earth and the train would still be moving relative to each other, and the train would still be the one moving relative to the earth, even if it were motionless in some "absolute" sense.

In contrast, in that scenario, the train would NOT be in relative motion with respect to "ether." It would only be in relative motion with respect to the earth. Again, the question is about relative motion (specifically the relative motion between the train and the earth), not absolute motion.

1 Reply

@layman,

http://i1378.photobucket.com/albums/ah99/davidrs1/noone_zps2ydbbowi.jpg

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@fresco,

Well, now, Fresco, aint that special?

What are you trying to "prove" here? That you don't understand alternative theories of relative motion, and don't want to, that it?

Or are you, perhaps, mistakenly trying to suggest that neo-lorentzian theories are "incorrect?"

The latter mistake would, of course, be quite common. Especially among know-it-all blowhards.

Any modern physicist would readily agree (at least if he was familiar with the research done on the matter), that SR and neo-lorentzian theories of motion are empirically indistinguishable.

1 Reply

@layman,

Quote:

Any modern physicist would readily agree (at least if he was familiar with the research done on the matter), that SR and neo-lorentzian theories of motion are empirically indistinguishable.

What a joke!!

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@fresco,

Einstein himself quickly rejected the theory of special relativity soon after he concocted it. He did so for a variety of reasons.

One reason was this: He felt that it was an inferior theory because it was merely what he called a "principle" theory, and not a "constructive theory."

A constructive theory, which he admitted would be vastly superior, would explain why the events it dealt with occurred.

A principle theory does no such thing. It merely makes assertions about what "must" happen without providing any theory about the physical factors which cause it. Einstein said he only proposed the special theory because he was "desperate," and because he didn't think current knowledge of electro-magnetic behavior could provide an adequate "constructive" explanation.

Al "reinforced " his theory by specifying a particular method of synchronizing clocks (now called "Einstein synchronization").. But, again, he readily admitted that such a choice was arbitrary, and not founded upon empirical experimentation.

This may be of some interest to Parados, also, who said this:

Quote:

The speed of light is constant in every frame of reference and constant from every direction.

0 Replies

Why in the world would Einstein suggest....

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