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firtree
firtree
1:28 AM
@ChrisWhite @ChrisWhite Feynman in his Lectures on Physics vol 3 focuses on finite dimensional cases for the greater part of the book.
 
 
8 hours later…
Phonon
Phonon
9:20 AM
@Danu hey man, any nice games lately?^^
 
Danu
Danu
@ChrisWhite but surely the notion of a free particle came earlier? It came up in my first QM course (following Griffiths' book)
@Phonon Not really, no, but do you want to play?
 
Phonon
Phonon
9:42 AM
@Danu yeah lets go
 
 
7 hours later…
Danu
Danu
4:21 PM
Guys, I'm going a little insane over here
I decided to reread the first part of Sakurai because it's so nice, but there's one formula where I can't seem to follow his reasoning (although I can reach the conclusion)
showing base-independence of the trace
sum_a <a| X | a>
=sum_{a,b',b''} <a|b'><b'|X|b''><b''|a>
where {a} and {b} are orthonormal bases
now the next step is what I don't get
=sum_{b',b''}<b''|b'><b'|X|b''>
so... sum_a <a|b'><b''|a>=<b''|b'> ?
this has to be really simple but I don't see it :P
 
Danu
Danu
4:38 PM
haha, I finally got it - man oh man
the embarrassment is real
 
 
2 hours later…
Phonon
Phonon
6:36 PM
guys what's the deal with those Galileo satellites that ended up in the wrong orbits? haha
have they said anything as to what's gone wrong?
 
 
2 hours later…
user54412
8:32 PM
@Phonon The real question is why are they spending money on this?
 
user54412
GPS already covers the planet after all
 
user54412
I can understand Russia, which always leaves open the possibility of war with the rest of the world, and I understand China, which has a desperate need to prove it can achieve the same things as the West. But why is Europe spending billions to duplicate something they already have?
 
Phonon
Phonon
8:52 PM
@ChrisWhite To be become independent of US? Specially considering the recent conflicts between them (NSA)
@ChrisWhite main reason may be business simply, a new source of revenue has clearly become the industrial use of GPS in Europe (looking for the link, read on this before)
@ChrisWhite so they can have a more reliable and manageable system probably, but again I think it's all these reasons added up together that may have motivated this motion
 
user54412
I know they claim this will make money, but I just can't believe that. The new system won't be any different from the one already in place.
 
user54412
Maybe I'm still annoyed at the ESA for Planck - all that money for astronomy, and they choose to duplicate WMAP rather than do new science.
 
Phonon
Phonon
from BBC: "It believes Galileo will bring significant returns to European economies in the form of new businesses that can exploit precise timing and location data delivered from orbit."
@ChrisWhite yeah I understand your point
@ChrisWhite and now if they don't manage to recover the ones out of orbit...imagine the loss...
 
user54412
@Phonon Yeah, big space missions can be political disasters if they fail. But at least here in a worst-case scenario they could replace the misbehaving ones.
 
user54412
Unlike JWST or something, where failure means the end of all future funding.
 
Phonon
Phonon
9:03 PM
haha yeah
then again maybe it's a purely political one,
from wiki: "Until 2000 the precision of the GPS signal available to non-US-military users was deliberately limited by a timing pulse distortion process known as selective availability, a capability removed from later GPS satellites."
haha maybe not^^
 
user54412
But also "The use of basic (low-precision) Galileo services will be free and open to everyone. The high-precision capabilities will be available for paying commercial users."
 
user54412
so basically Galileo will restrict quality data the same way the US used to do, except the US no longer does it
 
Phonon
Phonon
yeah I guess you're right
doesn't make much sense, all of which points back again at political reasons, I mean for example the fact that the US could deny its GPS services after a political disagreement between US-Europe e.g., something that EU should consider in long term.
but is it really worth the money and commitment as you say... one could argue that EU could have used this money elsewhere, and simply kept its relations in good terms with the US haha
 

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