Comments for 4by12

Comment on Twin Paradox in a Closed Universe by Guy Gur Ari

Guy Gur Ari — Sat, 05 Dec 2009 19:15:08 +0000

Bob receives both photons at the same time. This statement is true in any frame of reference, so Alice will agree with it.

Perhaps it will be easier to think about it another way. Suppose only Alice exists. She sends out two photons simultaneously and then measures the time difference of their arrival. She then accelerates a bit and repeats the experiment. In the second experiment, she will measure a different time difference.

If Alice accelerates by a certain amount, she can make the time difference between the received photons vanish. Alice then knows she reached the special rest frame.

Comment on Twin Paradox in a Closed Universe by amir

amir — Sat, 05 Dec 2009 18:17:45 +0000

so why can’t one argue that Alice sees bob move and so she sees Bob getting one of the signals before the other. still the same experiment leads to different results but this does not show which frame is the special one. I do not know much about GR but know a bit about special relativity so if you could explain using that I will appreciate it.

Comment on Correct arXiv authors in Google Reader by Carlos

Carlos — Mon, 23 Nov 2009 08:10:54 +0000

Thanks

Comment on Legendre Transform by sivaramakrishnan

sivaramakrishnan — Mon, 19 Oct 2009 12:34:12 +0000

nice post!

Comment on No More Time Waste by sandrar

sandrar — Thu, 10 Sep 2009 14:28:37 +0000

Hi! I was surfing and found your blog post… nice! I love your blog. Cheers! Sandra. R.

Comment on How to push GMail, Twitter to your iPhone with Prowl by Anonymous

Anonymous — Tue, 11 Aug 2009 14:22:42 +0000

Yes, I guess it’s the right thing to do, even though it’s a bit embarrassing.

Comment on How to push GMail, Twitter to your iPhone with Prowl by Stephan

Stephan — Thu, 06 Aug 2009 14:10:45 +0000

Very cool. Thanks for the patch of Net::IMAP::Client, although inelegant. Maybe you want to submit the patch to the original author?

Comment on A Short Note on the Poincaré Algebra by Dan Elharrar

Dan Elharrar — Mon, 25 May 2009 10:44:34 +0000

To me, and to generations of French kids, there is only one Casimir.

Comment on Correct arXiv authors in Google Reader by ggg

ggg — Tue, 19 May 2009 09:31:11 +0000

thanks for this, I have been waiting for ages for Google to fix this problem!

Comment on Complex Square Root by Guy Gur Ari

Guy Gur Ari — Tue, 24 Mar 2009 15:16:51 +0000

Yes of course. Perhaps the post was not clear. My only point is this: With the reals, the mistake is easy to spot. More importantly, one can work with a definition (sqrt = positive root), using which algebra behaves as you expect.

With the complex numbers the mistake is more subtle, and there is no such convenient definition for sqrt. Seemingly innocent manipulations often conceal mistakes, as one must always be careful when crossing the branch cut.