Time???????????

[Skudd]

I was driving last night and had Radio 4 on as usual. They were talking Einstein stuff and got on to time being a funny old thing, I wasn't listening too hard, but they did say something about putting a clock in a plane, flying somewhere and back with the clock then showing a different time to the clock that stayed still, also something about twins, one going to space and aging differently to the one on earth when they got back. They also talked about rubber mats a bowling ball and light, but I was going through road works at the time so didn't listen.

Does the plane thing actually work in reality and has anyone actually seen it themselves in action?
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[Tungtvann]

Time slows down the faster you go. Supposedly, what the fuck does this Einstein guy know.

https://en.wikipedia.org/wiki/Time_dilation

Here you go, yes, it's real.

[DrDonnyBrago]

[MarJay]

They've proven it by building two identical atomic clocks, putting one on a space station and another underground. They then drift out of sync from each other.[/list]
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[Derivative]

Yes, the plane experiment has been done. The change is on the order of nanoseconds but it has been measured (we have very accurate clocks nowadays).
https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

Special and General Relativity are fairly well tested.

https://en.wikipedia.org/wiki/Shapiro_delay
Massive objects delay light signals.

https://en.wikipedia.org/wiki/Gravitational_lens
They also pull light in as if it were massive.

Loads of other experiments out there.
I have an exam on special and general relativity in a week's time.

https://www.amazon.co.uk/Wonderful-World-Relativity-precise-general/dp/0199694613

This book is good reading and as I recall it doesn't really need anything other than basic GCSE level algebra to get through.

Its' mathematical big brother is our course material.

If you're wondering why the effect on planes is so small, it's because relativity produces weird effects in proportion to speed - but the benchmark is the speed of light (300,000,000 metres per second). A plane travels something like 300 metres per second (I had to double check that one because it sounds mental. But 600mph is about 1000km/h is about 0.3km/second).

[stinkwheel]

Yes, it's been tested and it does happen. A fast clock runs more slowly.

They can now measure this effect by having two super accurate clocks as little as 12" above one another (the higher clock is moving faster as the earth rotates).
C.W. Chou, D.B. Hume, T. Rosenband and D.J. Wineland. Optical Clocks and Relativity. Science. Sept. 24, 2010.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Islander]

Oh it works - GPS signals have to compensate for it. The concept has been verified experimentally using atomic clocks too. Gravity wells affect time as does velocity.

[Copycat73]

[Lord Percy]

Also there's length contraction. So the clock in space my have a longer life, but it is then shorter than its clock brethren!

[G]

[Islander]

No, the beam would be travelling at the speed of light with respect to the person holding the torch even if they were travelling at 99.9% of the speed of light themselves. It's all to do with referential frames.

[daemonoid]

[Derivative]

Yes.

The point is that the beam travels at c in all frames.

So if you have a laser pointer on your spaceship travelling 0.999c, you observe the laser beam travelling at c.

A guy on a stationary rock watching you doesn't see the laser beam at 1.999c or 0.001c, he sees it travelling c. So he reckons you're going nearly as fast as the beam.

The bit that does change is that he'd see it doppler shifted (i.e it'd change in wavelength and thus colour).

[stinkwheel]

The speed of light is constant BUT light does not travel at a constant speed.

It can go at walking pace in some substances and can even be stopped then restarted. It'sa still travelling at the speed of light.

The important thing to remember is that it is a constant (c) in that substance. It's the fastest thing that can travel in that substance and will always be travelling at the same speed relative to anything else in that system, regardless of how fast and in which direction that object is moving.

Weirded out yet?
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Frost]

It's confusing because light traveling at any speed is by definition going at the speed of light. Lightspeed on the other hand is the maximum speed anything can ever travel at and is the speed light travels at in a vacuum.

[keggyhander]

I know my chemistry and biology but this physics stuff is beyond me.

[Sload]

Er...

https://advanceproprecovery.com/wp-content/uploads/2013/01/Thinking-man-stop-my-sale.jpg
https://meremortalblog.files.wordpress.com/2012/11/mind-blown.jpg?w=412
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[Skudd]

I blame Radio 4 for making me think about stuff.

Women's hour is a mine field.
____________________
Famous last words of Humpty Dumpty. " Stop pushing me "
Petty Anarchists look at "1984".............. The Visionary looks at "Animal Farm".

[stinkwheel]

[cimbian]

[Derivative]

[Rogerborg]

[Skudd]

[mcgoogle]

what was the experiment someone setup where the act of observing said experiment change the results
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[trevor saxe-coburg-gotha]

Schroedinger's cat? That was just a thought experiment though.
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