# Why Does Time Slow Down or Speed up?

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1 hour ago, phyti said:

From reading his 'relativity' manual, he knows he has two options.

1. remain an anaut moving at .3c, or

2. assume a pseudo rest frame, with Q approaching him at .3c.

Choosing a reference frame doesn't determine what happens. His trip happens in all reference frames. You choose a reference frame  to measure/describe what happens, and the measurements from both reference frames implied here are valid.

1 hour ago, phyti said:

When the anaut twin returns to the earth younger than the other, isn't that proof that the anaut twin biological processes occurred at a reduced rate, even though the anaut was not aware?

Only relative to various observers. For the traveling twin, the biological processes occurred at the usual rate (1 s/s). The traveling twin *is* aware of the difference in aging. She can calculate the aging of Earth, and she can also see it happening.

1 hour ago, phyti said:

Inanimate muons need someone to speak for them.

No. This is just justifying misunderstanding SR.

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On 9/8/2019 at 3:54 AM, Strange said:

It depends on what you mean by "real".

When you say things like:

You seem to be saying that something physically changes in the length of the tape and spacecraft. And similarly with the clocks that measure time dilation.

That doesn't work because we are talking about relative measurements. How could another spacecraft speeding up or slowing down cause your astronaut's rule to shrink and expand?

And how much should the ruler shrink? I am stationary (in my frame of reference) so my ruler is 100% of its normal length. When a spacecraft flies by at 10% of the speed of light then my ruler is now 0.5% shorter. But if, at the same time another spacecraft flies past at 20% of c, then my ruler is 3% shorter. So which is it? It can't be both.

So, yes, length contraction is "real" but it isn't something that changes in the "moving" object, it is just a change in relative measurements.

[Ships moving past your ship at various speeds don't alter your equipment. Their speed does alter their measurements. It's the same as moving observers assigning different x and t coordinates for the same event, based on their relative speed.]

md65536;

Because time dilation is real.

[Yes]

And yet, the atomic clock recorded time at one second per second, never slowing down or "being affected" by time dilation in its own frame.

[No. The atomic clock recorded a fixed number of cycles of activity for cesium atoms, which represented a standard unit of time = 1 sec. The cycles differed from those of the ground based clocks due to their relative motion. The clocks frame was that of the aircraft, thus the differences had to have occurred in flight

The purpose of the experiment was to detect differences between static ground based clocks vs moving clocks. They already knew the answer to clocks in a common frame. The evidence was in the clocks, and not the perception of the passengers.]

[If you say the ground based observers detected td via electronic communication, then it occurred in the clock/plane frame and the passengers could not detect it. That is not the same as it didn't occur because none was detected in the plane.]

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34 minutes ago, phyti said:

Ships moving past your ship at various speeds don't alter your equipment. Their speed does alter their measurements. It's the same as moving observers assigning different x and t coordinates for the same event, based on their relative speed.

Exactly. So it is purely a matter of how other people measure your length and time. Your rulers and clocks do not change.

And yet you still seem to be saying that there is some change thing place in the clocks and rulers.

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19 hours ago, Strange said:

Exactly. So it is purely a matter of how other people measure your length and time. Your rulers and clocks do not change.

And yet you still seem to be saying that there is some change thing place in the clocks and rulers.

How was the MMX resolved?

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Just now, phyti said:

How was the MMX resolved?

What do you mean? It was attempting to detect a (relatively) stationary medium that light travelled through. It failed to detect that because it doesn't exist. Not sure how that is relevant.

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On 9/10/2019 at 11:56 AM, Strange said:

What do you mean? It was attempting to detect a (relatively) stationary medium that light travelled through. It failed to detect that because it doesn't exist. Not sure how that is relevant.

Wasn't length contraction of the slab in the x axis the solution?

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38 minutes ago, phyti said:

Wasn't length contraction of the slab in the x axis the solution?

That was the ad-hoc explanation from Fitzgerald-Lorentz contraction. This was unsatisfying, as ad-hoc explanations tend to be, and was tossed when relativity was found to be a viable alternative and no undetectable aether was required.

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