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Ekkehard Friebe Ekkehard Friebe ist männlich

Dabei seit: 23.11.2005
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How to test your Physics teacher about relativity?
by John Doan


I'm lucky to learn Physics with a teacher who always tells me what he knows. And what he doesn't. He told me that he'd been told to tell us that Einstein's theory of relativity has revolutionized mankind's awareness of time and space but he didn't fully understand it.

"Then why do we say it's the greatest theory?" I protested.
"Because all our scientists have said it, all books have said it, and all experiments have confirmed it," he replied.
"But you said that you don't understand it?" I asked.
"Even an idiot can still say he doesn't understand Einstein, it doesn't mean Einstein is wrong."

And it works. I became quiet then, went past Year 12 Physics with top mark, and no one suspected I was an idiot. You see, if you keep your mouth shut or keep praising what others praise, no one would ever know. Does your teacher know you are an idiot? Or the other way, do you have a teacher who claims he understands Einstein? How can you be sure if your Physics teacher fully understands Einstein's theory or not? And for that purpose, here is a test, any Year12 student can put to his Physics teacher. And be warned, he could fail (unless he has read this book.).

1. What is time dilation?

Einstein's theory of relativity is about a lot of things. But the most bizarre and for which the theory has become so famous of are its revolutionary concepts about time dilation and space curvature. Being the most crucial, yet the least defined, they have confused so many people for so long that even some scientists have feared to confront their validity. So before let your Physics teacher get away with hundreds of math equations which have nothing to do with our question here, demand him to tell you firstly and in straight words what time dilation is.

2. Does that mean two any identical clocks moving away from each other, would show different readings when being compared to each other after the trip?

Forget about whether time would appear to slow down, or actually slow down during the trip (Who cares? We don't even know what'd happen when they're at rest, let alone one is moving). Only ask him what happens after the trip, when two clocks are brought back to compare. Ask your teacher to answer you in straight words, yes or no. Read the section "Interview with Einstein," and ask him to explain why different physicists interpret different ways about that concept. Ask him which answer is right, which is wrong, and which is Einstein's original answer? If the answer is yes, ask him when being compared at rest, which one has a real faster reading than which one? Why is there one faster than another, when both see the other run slower in uniform motion? And remind him, we're talking only about uniform motion where acceleration is nil, how on Earth would we know which one is moving, and which one is at rest when Einstein already said uniform motion is relative. If the answer is no, then ask what Einstein's time dilation equation is for? Just for fun or what?

3. What sort of clocks should be used in those experiments?

Would any clocks behave in the same way? Would they run slower at the same rate? And what rate is the real rate for all clocks? If clocks don't behave in the same way they're supposed to run according to our equations, would we call them wrong, or that our equations are wrong?

4. What is time?

Your Physics teacher might run over you with hundred carefully-verified time dilation tests, ask him how could we say we have experimentally confirmed time dilation, when we don't know what time dilation is. Ask your teacher if he or she knows what time is? If he says yes, then ask him why all books written by various physicists and even Professor Paul Davies say they don't know what it is. If he says no, then ask him then why we can talk about time dilation without knowing what time is? How can we possibly say we have successfully landed on Mars, when we don't even know what landing on Mars is?

5. Talking about time dilation confirming experiments, ask your teacher what actually those tests have shown?

That time dilation is due to uniform motion or in fact just due to gravitation or acceleration change? Is it possible that time dilation never caused by uniform motion but only by acceleration or gravitation change or even something else? Your teacher might mention about experiments with waterfall clocks, or clocks at different gravity locations. If so, where is the equation?

6. Is Einstein's time dilation equation self-contradictory?

Einstein's time dilation equation is exclusively written for uniform motion expressed in the form T/To = f(v). Since uniform motion is relative, we can also say To/T = f(v) and that means T/To = To/T. Does that mean T = To? Time dilation can only make sense if T is not = To. Doesn't that mean Einstein's time dilation is self-contradictory? What use can we have for a self-contradictory equation? And if so, does that mean Einstein's time dilation original equation is wrong?

7. What about length contraction equation?

Time dilation is often the most asked question in Einstein's special relativity, in fact it's length contraction that makes Einstein's equation so hard to make sense. Look at Einstein's LC equation, ask your teacher what Einstein means by L= Lo √ (1 - v2/c2)? What is L? What is Lo? The simplest and easiest interpretation is, and this is what any kid can say, Einstein means the length of the spaceship would be measured as shortened by the Earth's observer, though it's always the same according to the astronaut (as his ruler in the spaceship is also shortened). But again, we're not interested in how the length of the moving spaceship would be measured by someone standing on Earth. We only want to know if we can use that equation to measure the length of the spaceship after landing on Earth? Would its length still be the same or not? Or in fact it has really shortened? Someone would say, after landing on Earth, as v = 0, so L = Lo, and so its length is still the same. If so, what we call it LC for? Would Einstein's time dilation equation mean the same, that upon returning to Earth, as v = 0 so T = To, and there's no time dilation at all?

On the other hand, if Einstein says L is the spaceship's length at the landing time, Lo is its original length at the departure time, and v is not the speed at that landing time, but has to be its average speed during the trip, then it would mean the spaceship's shortened length is only due to v, regardless how long it has traveled, wouldn't it? And what happens if during the trip, apart from a normal flying period, the spaceship sometimes flips up and flies sideway, its length becomes now vertical height, and cannot be affected by LC equation, what would happen when it returns home? In two cases, would there be any differences to the spaceship's length despite the same v? Can we still use Einstein's equation to measure the spaceship's length or not? Whatever answers your teacher might give, be careful he might keep changing his definitions about L, Lo, v, to suit his explanations as he pleases. And he cannot do it. An equation must have its own purpose. We cannot use that LC equation to calculate the spaceship's weight, temperature or its height change, can we? We can only use it the way it's originally written for. Therefore, we have to understand clearly what those involved variables stand for. What definition a variable is given prior to the equation, the same definition has to be used when that equation is applied. Let's not forget we never argue with Einstein about his math, as we know math is always right. The whole idea is simply to understand what is it that Einstein says in his equations so we can use them.

What is L? What is Lo? What is T? What is To? And what is v? That's all we ask. Does your teacher know what Einstein means by those? (see "Twenty questions only Einstein can answer?" )


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How to test your Physics teacher about relativity?

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Dieser Beitrag wurde schon 1 mal editiert, zum letzten mal von Ekkehard Friebe am 13.02.2009 10:03.

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