Paradoxes and Dilemmas

nderosa
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22 years 2 months ago #3359 by nderosa

Replied by nderosa on topic Reply from Neil DeRosa

AB,
I saw your message, but a lot of it is beyond me, so I'll let Tom pick it up if he wants to whan he returns from his trip.

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nderosa
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22 years 2 months ago #3124 by nderosa

Replied by nderosa on topic Reply from Neil DeRosa

While reading the new article by TVF, "Physics has its Principles," I thought I would try again. The first thing I would stress is that this is a logical and not a scientific exercise. It depends on the "major premise" being factually correct if the conclusion has any hope of being so.

"clocks may change rates, and they apparently slow down in a gravitational field or moving relative to such a field." [TVF]

We can take as our principle then (our major premise), that clocks slow down in a gravitational field when moving relative to that field. Examples would be a clock in a fast moving train, or a jet, or a satelite--all moving in earth's gravitational field. This, I think, is consistant with Lorentzian Relativity (LR).

Now I'm going to say that the second part of the above quote, "or moving relative to such a field," could be seen as violating the law of causality if the moving object (and clock), is no longer moving in that gravitational field. The reason is that the cause which slows down the clock (ie., the gravitational field), is no longer present. This is why I said (in my previous piece on this topic), that clocks may not slow down at all in an interstellar trip (if Lorentz is correct and not Einstein), as in the "twins paradox" scenario; and an experiment could fairly easily be done to test the possibility.

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AgoraBasta
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22 years 2 months ago #3125 by AgoraBasta

Replied by AgoraBasta on topic Reply from

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>Now I'm going to say that the second part of the above quote, "or moving relative to such a field," could be seen as violating the law of causality if the moving object (and clock), is no longer moving in that gravitational field. The reason is that the cause which slows down the clock (ie., the gravitational field), is no longer present.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>The real requirement is motion wrt any local inertial frame. A local inertial frame in gravitational field must accelerate wrt source of gravity, and this acceleration must be different for different distances from the field source.
You may also consider the space (or vacuum) as filled with an acceleration field that is zero when far away from any mass. But this zero is nevertheless meaningful, so that physical change of ref frame by the observer to the ref frame of moving clock reveals the presence of that acceleration field and defines motion wrt it to the precision of an offset that's common for both the clock and the observer.

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Atko
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22 years 2 months ago #3135 by Atko

Replied by Atko on topic Reply from Paul Atkinson

Speed, or velocity only makes the clock appear to go slower (according to GR). The actual paradox in the twin paradox is that if each twin were to observe the other, they would both perceive their sibling's clock to be going slow, and therefore each "must" be aging more slowly than the other because each is travelling away from the other at the same relative speed. If you were to conduct a thought experiment where the twins lived in a bounded, curved universe where travelling in a straight line brings you back to your starting point, and if the travelling twin were to blast off, circumnavigate the universe and return to the point he started, where his twin, possessed of the patience of Job, waited for him, then, disregarding gravitational/acceleration effects, he would still be the same age as his brother. Theoretical time dilation only occurs as a result of either gravitation or acceleration, as has been commented on earlier in this thread.

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tvanflandern
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22 years 1 week ago #3841 by tvanflandern

Replied by tvanflandern on topic Reply from Tom Van Flandern

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>[N. DeRosa]: Some scientific theories can't be understood no matter how carefully we read them. Einstein's theory of Special Relativity is one such theory.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

I used to think that too, but now understand that SR involves no logical contradictions. It does violate common sense, and is almost certainly wrong. But there is a way to understand it that is at least possible. The key is to abandon our intuitive sense of a universal instant of “now” and substitute a concept of time that varies from frame to frame, even though observers cannot perceive any changes as they switch frames. Nonetheless, if SR were right, time in other frames would be a mixture of past, present, and future at what we perceive to be “now”.

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>If a traveler leaves earth in a rocket ship and is soon moving at a speed approaching the speed of light;<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

For those who did not see our MRB article on this in the Sept. 15 issue, we noted that this and all “twins paradox” examples can be done without accelerations. (I recommend that readers check out the MRB article before jumping in. Understanding the context is key to understanding the discussion of it.)

The point was to show that accelerations have nothing to do with resolving the paradox despite many textbooks saying otherwise. However, cyclotron experiments have shown that not even accelerations of 10^19 g have any effect on clocks. The point is important because attempts to invoke accelerations can only lead to more denial and controversy because it can always be shown that an acceleration was inconsequential to what happened.

For example, the spacecraft twin did not need to accelerate away from Earth. The spacecraft could have come by from infinity, with the “twin” born just as the spacecraft passes Earth. Likewise, instead of a turn-around, the spacecraft could be replaced by a spacecraft coming from the opposite direction carrying a twin of identical age as they pass. Or the original twin could continue on from Alpha Centauri to Beta Centauri instead of turning around, and be compared to the ages of children on Beta Centauri that the Earth-bound twin will certify as having the same birth moment as the original twins. Nothing is changed about the circumstances or the conclusions by these substitutions, which avoid accelerations. All doubts about these or innumerable other variants can be definitively removed by the trick of carrying along a “GPS clock” on board the spacecraft.

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>if he travels at a constant speed for say, eight years, earth time, and then returns to earth; he will be much younger (according to the theory), having aged much less than his contemporaries who remained back on earth. But according to SR, there is no preferred inertial frame. It would be equally correct to say that the earth departed from the rocket ship at near "c," and hence earth's inhabitants would have aged much less than the rocket traveler who remained at rest in his own little inertial frame.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

This is only true if there is a universal instant of “now”. But if relative travelers are slipping into each others’ past or future, then the logic just quoted does not apply. Each twin can be getting younger relative to the other at the same time. If the spacecraft turns around, inferred Earth-time at the spacecraft jumps from the past to the future (and back again if the spacecraft turns around again) without affecting the age of the twin that turned around. If that twin returns to Earth to verify these changes, they are indeed verified. Although accelerations per se do nothing, switching inertial frames changes everything at a distance. But these changes cannot be observed when they happen because of the finite speed of light.

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>But the intuition - that is to say, the logical mind - rebels from such antics, and none of the experimental evidence ever supported them. Their only support lies in "counter intuitive" math / logic, buttressed by subjectivist philosophies.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Intuition and logic are not the same thing. SR is logical (in the sense of internally consistent) but anti-intuitive. Be content that it is almost certainly wrong. You might succeed in convincing a relativist of that, but never that it is illogical.

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>Then we come to Lorentzian relativity (LR), which is much closer to the way the common sense perceives the world—but not quite. In LR, clocks (and time for all intents and purposes), slows down for the traveler relative to the local gravitational field (e.g., earth). As I said, the intuition could accept this if this was indeed the way the world works. But is it?<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

In LR, nothing ever happens to time. The change in clocks is like the change in a pendulum clock when the temperature increases. The ticking slows, but nothing happens to time. The fact that the ticking of a moving clock slows is verified (for example by atomic clocks on board GPS satellites) to roughly a precision of a part in 7,000.

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>1- The relativistic factor gamma, still approaches infinity as v² approaches c². This means that, either c is the "speed limit," or that time goes backward as c is reached and surpassed, or that the formula is not a true representation of reality.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Time cannot go backwards because time cannot be altered in any way for any observer in LR. Hypothetically, your atomic clock might start ticking backwards, but that would just be a clock running backwards in forward time. In reality, the atomic clock would not run backwards. It would break because the transitions of cesium atoms could not be completed. The Lorentz time transformation correctly represents what happens to the clock, but says nothing about time.

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>2- Originally, (in LET), the ether was considered to be the preferred frame. (This is like the old idea of absolute space.) For various reasons, this was replaced by the idea that the local gravitational field is the preferred frame. Either way, LR resolves, as Dr. Van Flandern points out, Dingle's, or the twins' paradox. Time slows down only for the traveler. But I can see no physical reason why clocks, or time, have to slow down relative to a local gravitational field when the traveler in his rocket ship is far removed from that field and beyond its sphere of influence—as when it is traveling in interstellar space.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Think of the aether as a medium filling space, but one that is very sensitive to local gravity. So aet