E=MxC Squared

[Solitary]

http://youtu.be/30KfPtHec4s

[josephpalazzo]

The second part of this video is here:

https://www.youtube.com/watch?v=G-R8LGy-OVs

However, the last part, starting at 6:55 comparing two clocks moving relative to each other, is misleading. What it says at 8:55 is wrong - that's what happens when someone hasn't a firm grasp on the subject.

[AllPurposeAtheist]

Those GPS signals are making you think it's really happening.. Illunimati!

[Solitary]

The second part of this video is here:

https://www.youtube.com/watch?v=G-R8LGy-OVs

However, the last part, starting at 6:55 comparing two clocks moving relative to each other, is misleading. What it says at 8:55 is wrong - that's what happens when someone hasn't a firm grasp on the subject.

Thanks for the second part of the video!  Explain why 8:55 is wrong in plain English. Seriously. Solitary

[josephpalazzo]

Thanks for the second part of the video!  Explain why 8:55 is wrong in plain English. Seriously. Solitary

In any experiment, one must define what is being measured. In SR experiments in particular, to know who is considered to be at rest wrt to a clock and who is in motion, wrt to a clock, is crucial to determine who will end up with time dilation. At the end of that video, the narrator makes the claim that one observer can consider the other observer to have time dilation, and vice versa, which is never the case.

Take the case of the twin paradox, where one twin stays on earth, and the second travels in a spaceship to a far distant star. In this case, the traveling twin carries one clock to determine two events: the departure of the spaceship and its arrival. While the earth twin must register the time of these two events with two clocks: one on earth, the other on that far distant star. So the travelling twin will experience time dilation, not the earth twin, even though one could argue that from the travelling twin's POV, she could say that she is at rest while her earth twin is moving away. It's not about the fact that motion is relative that time dilation occurs but the fact that in one case, the travelling twin, the clock is moving. For the earth twin, his two clocks are NOT moving, hence the earth twin does not experience time dilation, but the traveling twin does.

[Solitary]

While the earth twin must register the time of these two events with two clocks: one on earth, the other on that far distant star.

Thanks for the reply! How does one on earth know what time it is on the clock on that far distant star? 

[josephpalazzo]

You need a partner stationed there - one of those aliens with green antenna... :-)

[Solitary]

Got it!  :alien2:

[josephpalazzo]

To test time dilation to a much higher precision, Benjamin Botermann of
Johannes Gutenberg-University, Germany, and colleagues accelerated lithium ions
to one-third the speed of light. Here the Doppler shift quickly comes into play.
Any ions flying toward the observer will be blue shifted and any ions flying
away from the observer will be red shifted.


The level at which the ions undergo a Doppler shift depends on their relative
motion, with respect to the observer. But this also makes their clock run slow,
which redshifts the light from the observer’s point of view â€" an effect that you
should be able to measure in the lab.


So the team stimulated transitions in the ions using two lasers propagating
in opposite directions. Then any shifts in the absorption frequency of the ions
are dependent on the Doppler effect, which we can easily calculate, and the
redshift due to time dilation.


The team verified their time dilation prediction to a few parts per billion,
improving on previous limits. The findings were published on Sept. 16 in the journal
Physical Review Letters.

http://www.universetoday.com/114879/time-flies-in-the-lab/