Why in the world would Einstein suggest....

@layman,

Quote:

What has me going however, is whether or not it matters which one of 'em had accelerated, i.e., after circumnavigating the Universe when they meet again coming from the other direction whether they find each other the same age

Once more the answer is that in order for the "traveling twin" to return to rhe common frame of reference he must have accelerated. In General Relativistic terms he has followed a shorter (space-time)"world line" to the meeting point with his non-accelerated (inertial) twin, which predicts he will BE younger. In the constant velocity stage of the travel Special Relativity says that neither twin has priority over "whose time is correct" . Each would SEE (through a telescope) the other's "clock" or "pulse rate" or "metabolic rate" as though it were running slow relative to has own. This has no practical or physical significance. It is a curiosity of observation equivalent to the Doppler effect in sound.

Whenever you read on relativity you need to remember two things.
1. "Time" defined as that which is measured by a clock. It has no meaning in its own right
2 "Measurement" requires involves light whose speed is independent of the relative speed of observers to the clocks they observe.

These points are the key issues on which Einstein departed from others.
Its results are counter-intuitive to everyday experience and are poorly understood as exemplified by the OP.

Now it may turn out to be the case that Relativity Theory eventually ceases to be mainstream because it does not sit well with Quantum Mechanics. But such a paradigmatic shift would not arise from amateur fooling with the mathematics. It would come from a transcendent theory subsuming both relativity and QM.

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Sorry Dale, the above post should have been addressed to you.

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@dalehileman,

BTW. I should have made clear that my reference to the Doppler effect was with respect to its status as "an observational curiosity" . The was no implication of mathematical equivalence.

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@barmpot,

Quote:

This has no practical or physical significance. It is a curiosity of observation equivalent to the Doppler effect in sound.

I hear what you're saying Barm but that's not how I had understood it: The relative velocity will have two separate effects, (1) a change in the other's apparent clock speed (and the wavelength of its light), up or down depending on whether they're approaching or parting, like the Doppler; and (2) a slowing--regardless of approach or parting--that can indeed later be confirmed as "real"

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@dalehileman,

Quote:

a slowing...that can indeed later be confirmed as "real"

Yes, Dale, I agree with you (as do the physicists) about what can "later be confirmed as real." The question of which one is "really" moving is one of both practical and physical significance.

Barm says:

Quote:

Each would SEE (through a telescope) the other's "clock" or "pulse rate" or "metabolic rate" as though it were running slow relative to has own.

But why is that? What is it that they actually "see?" The evidence suggests that it is not what they "see," but rather what they deduce, that leads them to the conclusion that "the other guy's clock is slowing down, not mine."

If, like Hafele and Keating, I am on a plane and assume that I am moving wrt the earth, then I will "see" the earth's clock going faster, not slower, due to the dilation effects of speed. And, according to their findings, I will be "right." If, on the other hand, I assume (as SR requires me to do) that I am motionless on the plane, and it is the earth which is moving, I will "see" the earth's clocks running more slowly than mine, but I will be wrong.

One's inferences about which of two relatively moving clock is slowed down depends entirely on one's premises. If I presume that I am moving, then I will conclude that my clock has slowed down and that "his" is going faster. If I presume the opposite, then I will come to the opposite conclusion.

Once again, BOTH cannot be motionless. If each of two relatively moving observers assumes that he is motionless, then at least one of them has to be wrong.

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@layman,

Quote:

If each of two relatively moving observers assumes that he is motionless, then at least one of them has to be wrong.

That's because of course in the absence of a "stationary ref" the idea of motionlessness is meaningless

But what has always bothered me about time-at-a-distance, three different observers at the same location in space can have three different ideas about that distant clock and yet all three are "real"

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@dalehileman,

Quote:

But what has always bothered me about time-at-a-distance, three different observers at the same location in space can have three different ideas about that distant clock and yet all three are "real"

Dale, I'm not familiar with how that could happen, but if it does, one thing is obvious, isn't it, to wit: Some theorist can "claim" that all 3 are real, but he could not possibly be correct when making such a claim.

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@layman,

Quote:

Dale, I'm not familiar with how that could happen,...

Marty and I each has a perfect ship capable of instant acceleration to (nearly) c. Long before our respective trips Marty and we had synchronized so to us at noon it's also noon on his home planet. However, unbeknownst to us Marty had left home at 11:55 so with his arrival here, to him it's still 11:55 back home. Though it's noon here, unbeknownst to you and unaware of Marty's trip, I had just launched hoping for a visit at Mars; so to me it's 12:05 there

Thus at a single location here on Earth, three different ideas of what time it is at that distant planet, and all three observations "real"

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@dalehileman,

Quote:

That's because of course in the absence of a "stationary ref" the idea of motionlessness is meaningless

And that's why SR cannot, in practice, forego the use of a "stationary" reference point. What good is a "theory" of motion" which simply tells you: "motion is meaningless/"

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@layman,

Quote:

What good is a "theory" of motion" which simply tells you: "motion is meaningless/"

The problem is semantic I'm sure. Not "motion ," but the notion of absolute motionlessness that's supposed to be meaningless

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@dalehileman,

Quote:

The problem is semantic I'm sure. Not "motion ," but the notion of absolute motionlessness that's supposed to be meaningless

Well, Dale, "meaningless" is a term used often by logical positivists who try to employ a "verificationalist" theory of "meaning." But no one subscribes to that discredited empistemological standard any more.

There is a difference between something being "unknown" and something being "meaningless."

The is a difference between something being "unseen" and that same thing being "non-existent." Solipsists will make no such distinction, though.

Say I put a guy in front of a door and ask he what he sees and he says "I see a door."

Now suppose I blindfold him and ask him what he sees and now he says "I see nothing."

That's not surprising, but does that mean there is now no door in front of him? I don't think so. But a solipsist would say "Yeah, that's exactly what it means. Now there "is" no door is front of him.

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@dalehileman,

Quote:

The problem is semantic I'm sure. Not "motion ," but the notion of absolute motionlessness that's supposed to be meaningless

Of course, that's not even true for SR adherents. According to SR, accelerated motion is absolute, not relative.

Well, granted, this says nothing about absolute rest, but motion can only be known if contrasted with a "lack of motion" (i.e., a state of rest).

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@dalehileman,

According to a physicist at the University of Callifornia, Riverside:

Quote:

Do moving clocks always run slowly?...The answer is no....One way to see how moving clocks might not run slowly is to consider an inertial clock being orbited by another clock that is so close as to be almost touching....This can only mean that the orbiting clock measures the inertial clock to be ageing quickly. The frame of the orbiting clock is accelerated, and the (inertial) clock that moves within this frame ages quickly, not slowly.

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

There are many implications of this, worth pursuing, but one immediate one that I would note is that we do have "real world" ways of determining who is moving, relatively speaking.

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@layman,

Consider this physicist's comments together with the "axiom" of SR called the "clock hypothesis" (which states that only speed, and not acceleration, effects time dilation).

An orbiting object can be "accelerated" in the technical sense of the term, but that acceleration will have no effect on the amount of time dilation if it simply maintains a uniform speed (which objects in circular orbit do).

What's that tell you?

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@dalehileman,

Let's assume there's a train, parked at the station, and it suddenly begins to move (it is now accelerating).

Let's say it continues to accelerate at a very slow rate, such as an increase of 1 mph. So, after 60 hours it is going 60 mph.

Now, according to what the physicist said, all during that entire 60 hours, a guy on the train will "see" an earth clock running faster, not slower.

Now let's assume that for one minute, the train quits accelerating, and maintains a uniform speed of 60 mph. Now, according to SR, the train passenger must assume that he is not moving, but that the earth is, even though, for the past 60 hours, the opposite was the case.

Now let's say the train starts slowing down at a the same slow rate of decrease (1 mph) until it comes to a complete rest with respect to the earth. During these 60 hours, the passenger also "sees" himself as "moving" and therefore also assumes that the earth clock is running faster than his, not slower.

What "magic" thing happened during that brief one minute (out of a total of 7,201 minutes) that would lead him to "suddenly" conclude that his clock was running faster?

My answer: Nothing. He wouldn't see it that way. Unless he is a fool.

The mere fact that he quit accelerating for one minute would NOT tell him that he quit "moving." The laws of physics (e.g. inertia) would in fact tell him just the opposite (i.e., that he is STILL moving, even though he is no longer accelerating).

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@layman,

Huh?

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@cicerone imposter,

You have a question, Cicer?

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@layman,

Summarized in one sentence, what is the difference to anyone?
Don't mind me, because I can misunderstand what people are trying to say.
My bad.

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@layman,

layman wrote:

Fresco, I'm afraid you strike me as being very long on ad hominem insinuations and very short on any type of explicatory exposition.
What's up with that?

I suspect that it is because your reply to everything is to simply deny reality over and over again, making all attempts to explain reality to you an exercise in futility.

-----

Does anyone have a good idea for a tag for topics like this?

Einstein Denial?
Relativity Denial?

Going to add both of those I think.

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@layman,

layman wrote:

that a man on a moving train does NOT know he is moving relative to the earth's surface, and not vice versa? Who in the world would get on a train, feel himself being accelerated, and then, once a uniform speed has been attained, conclude that the trees, stop signs, houses, etc. are moving past him while he remains completely motionless. Isn't this rather absurd?

Who would ask the conductor if Chicago stops here?

Yet this presumption is the sine qua non of special relativity theory, isn't it?

Just for the record, special relativity doesn't say that the passenger doesn't know he's moving relative to the surface of the Earth. It says that the laws of physics are the same in all unaccelerated reference frames, that there is no experiment you can perform on the train which will show that you are "really" moving, and that, in fact, there is no such thing as being really at rest or really moving, except with respect to a specified object. A train moves relative to the surface of the Earth, but the Earth's reference frame is no more "really stationary" than any other unaccelerated object, including the train. For the purposes of this discussion, I'm ignoring the fact that the Earth actually is in accelerated motion due to its orbit of the sun.

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Why in the world would Einstein suggest....

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