Why in the world would Einstein suggest... 2

@Olivier5,

Quote:

The paradox can only be solved if one considers that at least one twin has a non-inertial movement, and thus their respective situation is not equivalent.

In what way does that "solve" it? Magic? What's the connection? If we had noticed that, just before take-off, the travelling twin put on a pair of gloves, while the earth twin didn't, would that also "solve" the paradox? After all, we would then know that "their respective situations [are] not equivalent," right?

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@layman,

Quote:

In what way does that "solve" it?

I've already quoted (verbatim) how Richard Feynman said it "solved" the paradox. I will now paraphrase his explanation:

He started off by saying that there was only a paradox for those people who believed that all motion is relative.

You've never directly answered this question, which I have asked many times, either: Do you, Ollie, now concede (contrary to many numerous prior pronounments you've made in this thread) that not "all motion is relative?" Yes, or no?

If yes, then perhaps you will understand Feynman's explanation.

He continued by noting that SR predicts that the moving clock will run slow. He then added that we knew the "space" twin was the one moving because we knew had had been accelerated. Pretty simple, eh?

According to Feynman then, of course the two situations are not symmetrical. Accelerated motion is absolute. One is moving. One isn't, at least relative to the other.

Is that also your reasoning?

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@layman,

Quote:

In the twin paradox, the twin making all the correct and accurate predictions about who is really older, and by exactly how much, is the one on the earth.

ANY of the twin can make the right computation. All they need to do is use an inertial (e.g. in this case sun-centered) frame of reference to plot their trajectories and compute their respective speed.

Just because one lives in a non-inertial object (eg in a rocket, or on earth) doesn't mean one cannot make computations using an inertial frame, for instance centered on the sun. A frame of reference is a mental thing, a product of our mind. You still don't get that.

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@layman,

You still don't get it... Oh well.

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@Olivier5,

Quote:

Just because one lives in a non-inertial object (eg in a rocket, or on earth) doesn't mean one cannot make computations using an inertial frame, for instance centered on the sun. A frame of reference is a mental thing, a product of our mind. You still don't get that.

Of course I get that. Are you ever going to answer a post, or will you, as always, just keep changing the subject with each post you make, each time saying little more than that you know things that I don't?

Are you suggesting, though, that, according to the official SR version, at least one of the twins is actually using the sun's frame of reference, rather than his own, to calculate the "true" time difference?

Quote:

All they need to do is use an inertial (e.g. in this case sun-centered) frame of reference

Let me also ask you this: How is it that you know the sun is "inertial?" I already explicitly noted some of the circular motions that the astronomers say it is making. And god only knows how many times I've told you that the sun is itself revolving around the center of mass of the solar system (the barycenter). Why is it "inertial" according to your definition?

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@layman,

You don't really want to understand this, Lay. You want to not understand it, and that's what you are doing quite successfully. Keep up the bad work.

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@Olivier5,

Quote:

You don't really want to understand this, Lay. You want to not understand it, and that's what you are doing quite successfully. Keep up the bad work

Ollie, your posts in this thread have been a complete joke and it's quite evident to anyone who is even casually familiar with this subject.

You claim to fully understand SR, and claim to be a zealous devotee of it, but you are constantly making factual claims which, if true, would necessarily disavow SR.

You consistently change your story and contradict your own pontific assertions (which you refuse to defend, when questioned, because you can't). Despite ducking all questions, you will later come back, re-asserting the same errors, while proclaiming "I ALREADY EXPLAINED THAT, YOU'VE ALREADY BEEN TOLD!!" You never "explain" anything. On those rare occasions where you purport to, your "explanations" are inconsistent and incoherent.

When any of your numerous misunderstandings are corrected by recognized authorities, you just say the authorities are wrong (if you respond at all). You make things up as you go, saying the opposite of what you said yesterday (or even in your last post) and merely pretend that whatever you are saying now is indubitably correct.

It is quite impossible to have any kind of intelligible discourse with you, I'm afraid. I'm not mad at you. I don't dislike you, but it is a total waste of time to try to talk to you about this topic, I'm afraid.

1 Reply

@layman,

You don't understand what you are talking about, Lay, because you don't want to understand it. The day you really want to understand this stuff, it'll be a piece of cake for you. Until them, you are condemned to making very little sense with the noise coming into your ears or out of your mouth.

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@Olivier5,

Quote:

You don't understand what you are talking about, Lay,

OK, Ollie, let's just leave it at that then. On most topics, you strike me as thoughtful, intelligent, and fairly well informed. But not on this topic, as I see it. You see it as being the reverse. So we'll just agree to disagree, and leave it be. Fair enough?

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@layman,

Sure thing. I recommend you try and get your head around that the concept of frame of reference. I tried to explain it, but to no avail.

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Speaking of the barycenter, absolute motion, and all...

How did Newton figure out the precise motions of the planets in the solar system? Where did he even start?

The story goes that he used the solar barycenter as his "preferred frame." What did he say about this frame? Did he say it was motionless?

No, he said there was no way to know that. It was, however, motionless with respect to everything else in the solar system, the sun included. With respect to that point, everything ELSE moved, but not it. That said, it, and the whole solar system, could be involved in all kinds of other complex motions relative to the universe as a whole, he said. But that wouldn't make any difference, for his purposes. Those motions, whatever they might be, were shared in common by everything in the solar system, and would therefore have no effect whatsoever on his calculations. To simplify his calculations, he simply treated it as being motionless.

So, then what? Newton used the background of the "fixed stars" as another "motionless" frame against which he could detect the relative motion of the planets. Did he say that "fixed stars" were motionless? No, he didn't. What he did say was that they provided enough of "close approximation," for his purposes, to be treated as such, though.

Newton thought that the "true" motionless point would be the center of all the mass in the universe. He readily conceded, though, that we would never be able to detect it, even if we "saw" it. Somehow, by calculating from his chosen "preferred frame," he figured it all out. He would have gotten a completely different result had he chosen some other supposed "motionless point."

To this day, astronomers follow his methods, which incorporate absolute simultaneity as a premise, to make solar calculations. For some strange reason they do NOT use SR. Go figure, eh?

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@layman,

Another way we know of the planets' orbit is by observing them and plotting them in the ideal frame for this work: a sun-centered one with star-oriented axes.

GR is said to explain Mercury's orbit better than Newton's mechanics. The technical term which you may know is "precession" - a family of movement types where an orbit or rotation has some sort of 'slant': it doesn't end its turn exactly where it started. The particular type of precession involved for Mercury is called perihelion precession, apsidal precession or orbital precession.

A gif is worth a thousand words:

http://upload.wikimedia.org/wikipedia/commons/8/89/Precessing_Kepler_orbit_280frames_e0.6_smaller.gif

Planets revolving the Sun follow elliptical (oval) orbits that rotate gradually over time (apsidal precession). The eccentricity of this ellipse and the precession rate of the orbit are exaggerated for visualization. Most orbits in the Solar System have a much smaller eccentricity and precess at a much slower rate, making them nearly circular and stationary.
(Wikipedia)

BTW, the reason we humans can treat the sun as inertial is the very very small size of its acceleration as compared to its current velocity. The effects are too small to be detectable. The sun's trajectory barely deviates from a straight line in any detectable manner over the period of a human life.

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@Olivier5,

Quote:

BTW, the reason we humans can treat the sun as inertial is the very very small size of its acceleration as compared to its current velocity. The effects are too small to be detectable. The sun's trajectory barely deviates from a straight line in any detectable manner over the period of a human life.

Not sure who you have in mind when you say "we humans," Ollie, but anyone who knows that much about the sun's acceleration and "trajectory" would not use it as frame of reference for solar calculations:

Quote:

The International Celestial Reference System (ICRS) is the current standard celestial reference system adopted by the International Astronomical Union (IAU). Its origin is at the barycenter of the solar system, with axes that are intended to be "fixed" with respect to space. ... the ICRF is important because it definitely does not exhibit any measurable angular motion since the extragalactic sources used to define the ICRF are so far away. The ICRF is now the standard reference frame used to define the positions of the planets (including the Earth) and other astronomical objects. It has been adopted by International Astronomical Union since 1 January 1998.

http://en.wikipedia.org/wiki/International_Celestial_Reference_Frame

1 Reply

@Olivier5,

While on this general topic, it might be worth noting that, for time purposes, astronomers use Barycentric Coordinate Time:

Quote:

Barycentric Coordinate Time (TCB, from the French Temps-coordonnée barycentrique) is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to orbits of planets, asteroids, comets, and interplanetary spacecraft in the Solar system. It is equivalent to the proper time experienced by a clock at rest in a coordinate frame co-moving with the barycenter of the Solar system: that is, a clock that performs exactly the same movements as the Solar system but is outside the system's gravity well. It is therefore not influenced by the gravitational time dilation caused by the Sun and the rest of the system.

Basically, it is the time that would be kept at the barycenter IF a clock there would not be subjected to gravity. Here it says it "is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to orbits of planets, asteroids, comets, and interplanetary spacecraft in the Solar system."

Notice that time in being treated as an independent variable, a al Lorentzian relativity, and not as a conglomeration with space which the minkowskian interpretion of SR calls "spacetime."

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@Olivier5,

Quote:

I recommend you try and get your head around that the concept of frame of reference

OK, I'll sure "try." If you really want to inform yourself about this topic, I would recommend that you ask yourself this question:

"What do I think the difference is between SR and LR?"

In the following post, I gave one example of the difference. There, LR and SR would treat the motion involved in a 5 day duration the same with the exception of ONE MINUTE. Ask yourself if this would be the difference in that case. Is this an actual theoretical difference between the two theories? Then ask yourself why (or why not).

http://able2know.org/topic/276564-2#post-5948252

If it helps you refrain from bringing up non sequiturs about "inertial" frames, just imagine the whole scenario taking place in deep outer space, with the clock on the "earth" just sitting there (on a platform in outer space) when this train begins to move in a perfectly straight line.

1 Reply

A few excerpts from Al on the topic of the ether, a question which arose earlier.

Quote:

Ether and the Theory of Relativity by Albert Einstein (1920)

Certainly, from the standpoint of the special theory of relativity, the ether hypothesis appears at first to be an empty hypothesis....but the hypothesis of ether in itself is not in conflict with the special theory of relativity....there is a weighty argument to be adduced in favour of the ether hypothesis. To deny the ether is ultimately to assume that empty space has no physical qualities whatever. The fundamental facts of mechanics do not harmonize with this view.

The ether of the general theory of relativity is transmuted conceptually into the ether of Lorentz if we substitute constants for the functions of space which describe the former, disregarding the causes which condition its state. Thus we may also say, I think, that the ether of the general theory of relativity is the outcome of the Lorentzian ether, through relativation.

According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time.

http://www-history.mcs.st-and.ac.uk/Extras/Einstein_ether.html

You can read the entire article for yourself, if you're interested. He makes it clear that he sees the ether of GR as different from Lorentz's ether, but it's not entirely clear to me just how.

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@layman,

Sure, sure, the barycenter. But that doesn't change the argument.

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@layman,

Why bother reading an oudated opinion piece by Einstein, about a vague idea he can't even explain. You've become a fan or what?

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@layman,

There is no difference between the two theories in term of what empirical data they predict.

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@Olivier5,

Quote:

There is no difference between the two theories in term of what empirical data they predict

.

So, then, you don't know, eh?

1 Reply

Why in the world would Einstein suggest... 2

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