Why in the world would Einstein suggest... 2

@Olivier5,

I would like to take this one step at a time, Ollie, but rather than respond to my last question, you just produce a long lecture that is not responsive to it.

To help clarify the issues, let me refer you back to your own statements:

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So what is Einstein to do -- trying to verify his new theory of relativity ... Einstein can rest, SR is consistent with all observed data...

You have improperly equated the utterance a correct factual claim with "proof" that a theory is correct here.

Let me give a crude, but simple, example of what I'm saying:

Suppose I propound a theory which claims, whether by direct postulate or necessary implication from those postulates, the "elephants do not exist." OK?

Now, let's suppose I say to you: "It is an obvious fact that elephants DO exist."

What would you say to me? Wouldn't it be something along these lines: "Yeah, you are absolutely correct about that, but you have just contradicted your own theory."

The fact that I made a true utterance does not "prove" my theory. That goes double if the statement of fact in question contradicts my theory.

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@layman,

It's important to understand that in this context, "accelerate" means something much wider than just "going faster". Any deviation in the direction of movement away from a straight line, any rotation, any change of speed, is a form of acceleration and makes a movement non-inertial.

Why all the fuss about inertial frames? Why do I say that the laws of motion as we know them only works in inertial frames? It's because they are the nearest thing you can get to a stationary frame. Let me explain in some length.

When one wants to predict the future movements of, say, pool balls on a billiard table, one needs a frame of reference to plot the initial position, speed and torque of the pool balls. In general, the billiard table itself provides a convenient frame of reference in this case. One will plot the balls in terms of their distances to the table sides, for instance. A pool player will do this unconsciously and intuitively, but a scientist will measure these distances as precisely as he can. As a result, they both can predict something like: If I can give the white ball this combination of speed, direction and torque, this and that will happen, and I can score big time...

Note that this assumes that the frame is inertial, ie in lay language, that the table is as stable and immobile as possible. Over the course of a pool shot, ie a few seconds, earth rotation does not matter, as the pool table moves almost in straight line over that short duration. Pool tables are usually located far from railway or subway lines, for instance. The subway tremor would "accelerate" the table up and down, introducing errors in the computation. Imagine that the billiard room -- instead of being in a quiet neighborhood, is bolted on the car on a large roller-coaster. The room now goes up and down and left and right and slows down and speeds up all the time... Thus the billiard table will not provide an inertial frame anymore. And sure enough, very odd things will start to happen to the balls, when viewed in that frame... Their behavior can no more be as easily predicted as before from within the room. They fly in all directions... A hazard really.

Does that mean that the laws of motion do not apply to the balls? No. But to describe the balls behavior in a way that fits the laws of motion needs an inertial frame, at a larger scale: a scientist modeling the entire roller coaster and the trajectory of the billiard table on it could try and predict the behavior of the balls. Good luck with that, but in theory it's possible.

When one realises that one uses a non-inertial frame, one needs to mentally 'step outside' that frame and find a better one, knowing there is no perfectly inertial frames.

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@Olivier5,

This is still off the point, but let me take a minute to respond to it, in the hopes that it might clear up some potential confusion later. You are confusing two things that are fundamentally different in this post. You say:

Quote:

Note that this assumes that the frame is inertial, ie in lay language, that the table is as stable and immobile as possible. Over the course of a pool shot, ie a few seconds, earth rotation does not matter, as the pool table moves almost in straight line over that short duration.

How far the table moves in that time, and whether or not the motion is strictly "in a straight line" or not, is irrelevant to the issues we are discussing (whether in SR or physics in general), so long at the motion is uniform This is what the "clock hypothesis" says, but it's nothing new. It is just a restatement of Galliean relativity, really. So long as the frame is moving uniformly, it irrelevant how far it moves (in a straight or curved line) during any given interval. Why? Because everything else will be moving right along with the table. The relationship BETWEEN the balls, side rails, and table surface will not change one iota--they all share the same "inertial" motion.

Now I agree that uniform motion in a line (straight or not) is radically different from sudden and radical changes in direction (such as an earthquake might cause). But simply assigning the label of "inertial" (or "non-inertial," as the case may be) is not what decides that difference.

1 Reply

@layman,

Quote:

I may be misreading you here. If all you are saying is that in SR all inertial frames are "preferred" over all non-inertial frames, then I agree.

Yes, that's what I am saying. Although it is not only true in SR but also in classic mechanics. As I was saying, "inertial" is the closest thing one can get to "immobile". Ideally, scientists were looking for an immobile frame. But no such thing can be found for a series of reasons. Everything moves in the universe, nothing remains static. But as Galileo discovered, all frames moving inertially share the same essential view point of the universe. One can easily translate the data from one such frame to another; the same laws of motion will work accurately with the data provided by all such frames, and the computation will be correct. We can't find a static frame, but it doesn't matter because ANY inertial frame will do just as well.

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@Olivier5,

I said:

Quote:

Now I agree that uniform motion in a line (straight or not) is radically different from sudden and radical changes in direction (such as an earthquake might cause).

To elaborate: particles accelerated to near light speed in a particle accelerator are always going in a circle. At VERY high speeds. With respect to any particular point along the path they take, the are making literally millions of "revolutions per minute." But does that mean the Lorentz transformations no longer apply, because the "physics" are different? NO.

Not in theory, and not as shown by empirical test. You can argue that the "changes in direction" for such a particle are extreme and "radical" all you want. That doesn't change the applicability of the LT, so long at the rate of speed** is uniform. What it DOES do is lead to predictions of some extreme changes in relative clock rates, etc.

** Actually, it doesn't change the applicability of the LT, even if the rate of speed is changing (it might, however, change the applicability of SR as a valid "theory of motion").

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@layman,

Quote:

How far the table moves in that time, and whether or not the motion is strictly "in a straight line" or not, is irrelevant to the issues we are discussing (whether in SR or physics in general), so long at the motion is uniform This is what the "clock hypothesis" says, but it's nothing new. It is just a restatement of Galliean relativity, really. So long as the frame is moving uniformly, it irrelevant how far it moves (in a straight or curved line) during any given interval. Why? Because everything else will be moving right along with the table. The relationship BETWEEN the balls, side rails, and table surface will not change one iota--they all share the same "inertial" motion.

No. That ain't the case in classic mechanics nor in SR. If the billiard room turn left, however slightly, the balls on the table will appear to move right by the same measure, and for no apparent reason if one doesn't know that the car has turned left. Only if the billiard room runs in straight line at constant speed can the players play normally. The laws of billiard motion as they know them will apply perfectly. As soon as the room brakes or accelerate, or turn left or right, the balls will go towards one side of the table or the other, because they tend to keep an inertial motion even though their immediate surrounding is not. Of course the rules of physics do still apply to the room, but we now need to include in our calculation the way the room is being accelerated, and to do that we need another, larger and hopefully inertial frame of reference to plot the room's own motion.

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@Olivier5,

Quote:

No. That ain't the case in classic mechanics nor in SR

.

You don't even read what I say, Ollie, such as:

Quote:

...so long at the motion is uniform This is what the "clock hypothesis" says, but it's nothing new.

In SR, it is NOT velocity which must be uniform, only instantaneous speed. I could quote and explain the clock hypothesis to you 1,000 times, and you would still just repeat the same mistaken claims, it seems.

That's one reason that it's virtually impossible to communicate with you.

There are other reasons, too. Such as that you won't stay on a topic and don't seem to display any real understanding of what's relevant to the topic under discussion. If you are asked one question, you will virtually always ignore it. When you purport to "respond" to it, you usually just assert some non sequitur. But usually you just change the topic by saying that something in the question was "wrong." You can go on like that ad infinitum, ducking every question and refusing to participate in any honest discussion, preferring to make one unsubstantiated assertion (which you refuse to explain or defend) after another.

It becomes quite wearisome.

1 Reply

@Olivier5,

Quote:

How far the table moves in that time, and whether or not the motion is strictly "in a straight line" or not, is irrelevant to the issues we are discussing (whether in SR or physics in general),...

See that qualification that I EXPLICITLY included in my post? I.e, "is irrelevant to the issues we are discussing?" We are talking here about the effects of motion on time dilation, not anything else (other than the factors contained in the LT).

If two rockets, side by side, are both accelerating at the same uniform rate (say 1 g) then, according to SR, they will keep identical time. It doesn't matter that they are accelerating FOR THAT PURPOSE, although it may make a difference for other purposes.

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@Olivier5,

Quote:

Only if the billiard room runs in straight line at constant speed can the players play normally

One (long considered conclusive) argument that Galileo ran up against was that, if the earth were rotating (or revolving in orbit), then a ball dropped from a ship's mast would land quite a distance away from the foot of the mast.

This was due to an acceptance of, and a reliance on, Aristotle's notion of motion. The assumption was that, as soon as the ball was not somehow "attached to" the ship, it would immediately lose all "impetus." Galileo's premise (which later became Newton law of inertia (more or less) was that releasing the object did NOT immediately stop all it's forward momentum. His claim was that it would continue to keep going at the same speed as the ship. He also had to posit that even the atmosphere itself was "carried along" by the motion around the sun---which explained why we feel not a "wind" generated by our motion around the sun (or our rotation, for that matter).

Standing on the shore, a ball dropped from a tower on a moving ship would "appear" to follow a parabolic path. But, to those travelling with the ship, it would simply fall "straight" down, because it maintained it's momentum, even though it wasn't "attached to" the ship.

In addition to orbiting the sun, we, as part of the solar system are ALSO revolving around the center of gravity in the milky way. The milky way galaxy is itself revolving around some inter-galatic gravitational center of mass. We are also moving at the rate of about a million miles an hour toward Leo. How could anyone EVER play a "normal" game of pool it your assertion if correct?

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@layman,

Quote:

...so long at the motion is uniform This is what the "clock hypothesis" says, but it's nothing new.

In SR, it is NOT velocity which must be uniform, only instantaneous speed. I could quote and explain the clock hypothesis to you 1,000 times, and you would still just repeat the same mistaken claims, it seems.

What do you mean by "it is NOT velocity which must be uniform"? For what purpose? If you mean: "for a motion to be considered inertial in SR", that is simply false.

The clock hypothesis as i understand it is not a theoretical necessity of SR. Thus, SR could be true even if the clock hypothesis was false. It is a calculation-oriented hypothesis, grounded in observation, saying that IN ORDER TO COMPUTE TIME DILATATION and other Lorentz transformations for an accelerating object, one only needs to care for speed, and can neglect changes in direction as without effect on the calculus. Thus one can treat a particle turning around an accelerator as if it was going straight, FOR THE PURPOSE OF COMPUTING ITS TIME DILATATION. Such a computation, to be correct, still NEEDS TO BE BASED ON MEASUREMENTS MADE USING AN INERTIAL FRAME OF REFERENCE so that the speed of the particle is measured correctly. This last point, much more fundamental to SR theory than the clock hypothesis, remains unaffected by it.

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@Olivier5,

Quote:

The clock hypothesis as i understand it is not a theoretical necessity of SR.

I didn't read a single word past this. It is a FUNDAMENTAL axiom of SR, according to the physicists I have quoted for you. All you are saying is that you really have no clue what the theory of SR says. As has long been clear.

And having it explained to you, over and over, in clear terms provided by reliable experts, doesn't do a damn thing to improve your pitifully inadequate "understanding," unfortunately.

1 Reply

@layman,

Alright, it's standard SR. Fine. Nevertheless, it remains "an assumption in special relativity. It states that the rate of a clock doesn't depend on its acceleration but only on its instantaneous velocity", and that's all. It says nothing about what an inertial frame or movement looks like.

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@Olivier5,

Since you have conceded the significance of the clock hypothesis, I will look at what you say in this post (at first my patience had been so exhausted that I didn't know if I would ever respond to another post of yours).

Quote:

Such a computation, to be correct, still NEEDS TO BE BASED ON MEASUREMENTS MADE USING AN INERTIAL FRAME OF REFERENCE so that the speed of the particle is measured correctly.

A measurement of relative time dilation doesn't have to be made "in" or "from" an inertial frame, to be measured correctly, if that's what you are saying. The "speed" being measured is simply the relative speed, not necessarily an absolute speed. Object A is moving at the rate of X relative to object B. Both A and B can measure this difference accurately, in theory.

As between two moving objects, the respective time dilation still depends on the speed difference (if any) between them, even if (1) both are inertial (2) one is inertial, and one isn't, or (3) both are accelerating. I just gave an example of case #(3) here.

These considerations can be very important, theory-wise, but it won't affect the extent of the DIFFERENCE between the two which is calculated.

Of course if one or both is accelerating, then the measurement made at any given instant may be different in the next instant, and the calculation may only be good with respect to the exact time it was made.

1 Reply

@layman,

The outstanding question (by Dingle) has still not been addressed, despite numerous red herrings arising which have served to avoid it:

Quote:

Now, then, back to this statement of yours:

Quote:
...both clocks are at rest as viewed from the earth surface.

Remember, the question is: how can Al know that a clock at the equator runs slower than one at the pole? Simply saying "the earth rotates" does not, in itself, answer that question, does it?

If a clock (or person) at the equator looks at a clock at the pole, it will not be moving, and vice versa, right? If that's true, how and why can Al say (in effect) that one is moving, and one isn't?

You have addressed it, of course, to some extent, at least. You could simply say that the clock at the equator is, as a matter of known fact, actually moving relative to the pole clock, and that's how he can say it.

But the real, underlying question is this: Does that claim then contradict the implications of his theory?

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@layman,

Quote:

A measurement of relative time dilation doesn't have to be made "in" or "from" an inertial frame, to be measured correctly, if that's what you are saying. The "speed" being measured is simply the relative speed, not necessarily an absolute speed. Object A is moving at the rate of X relative to object B. Both A and B can measure this difference accurately, in theory.

If you believe that, i have a great pair of twins to sell. Each twins is older than the other one...

1 Reply

@Olivier5,

Quote:

I said: The "speed" being measured is simply the relative speed, not necessarily an absolute speed. Object A is moving at the rate of X relative to object B.

In response, you said:

Quote:

If you believe that, i have a great pair of twins to sell. Each twins is older than the other one...

Well, that's an interesting claim. Care to elaborate? Somehow, you don't seem to believe in SR, if you say that.

1 Reply

@layman,

As a matter of physics, the law of inertial would also tell them they MUST (still) be moving, even though their motion is now uniform. SR assumes that the opposite is true, ignoring the law of inertia and all common sense (such as that it takes a constant consumption of fuel to keep the train moving and that there is no apparent "force" which is causing the entire earth to move while you remain motionless).

Why are you so Gung Ho about a theory that can't be demonstrated or proved?

“What we think, or what we know, or what we believe is, in the end, of little consequence. The only consequence is WHAT WE DO.” John Ruskin (1819 - 1900)

“When we remember we are all mad, the mysteries disappear and life stands explained.” Mark Twain

1 Reply

@Rickoshay75,

Quote:

Why are you so Gung Ho about a theory that can't be demonstrated or proved?

I'm not gung ho about special relativity, Rick.

I 'm not what I would call "gung ho" about lorentzian relativity either. But I do think that it's far superior to SR when it comes to correspondence to objective reality.

I've said why, many times during this thread (which includes the previous thread of the same title) most recently on page 5 of this "new" thread. Here, I'll just cut and paste it for you, how's that?:

Quote:

Briefly, I only object to it insofar as it's advocates claim that it represents "reality." Accepting that claim requires one to accept utter solipsism, to disavow logic, to disregard known laws of physics (such as the law of intertia), etc.. And students are indeed browbeaten into accepting such things. There are other reasons, but those are at the top.

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@layman,

I'm just pulling your leg.

In SR, an inertial (moving in straight line, not turning, not accelerated, not slowing down) frame of reference is still required to calculate anything correctly. Until you understand that, you won't be able to understand much.

Confusing inertial with non-inertial frames and considering them equivalent is the mistake at the basis of the so-called "twin paradox". Hence my joke. 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. Using an inertial frame of reference, eg sun-centred, one can accurately compute their time difference.

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@Olivier5,

Quote:

I'm just pulling your leg.

Hmm, where to even start with this post? How about here:

Quote:

Using an inertial frame of reference, eg sun-centred, one can accurately compute their time difference.

So, are you saying that this is the "preferred" frame that gives the "correct" answer, whereas different frames (such as the frame of the travelling twin) give the wrong answer?

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. Would your "sun-centered frame of reference" give a different answer than he got?

1 Reply

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