Orbis non sufficit
Friday, March 28, 2008
Greatest theme ever
Thursday, March 20, 2008
Reading chair
Ok, I have decided my office needs a decent chair for me to read in, i.e. some kind of cushiony armchair. Also some kind of footstool. So, if any of you happen to see such a chair in any kind of reasonable condition lying around in hard rubbish or someones unlocked house then by all means grab it for me :).
Ok, I have decided my office needs a decent chair for me to read in, i.e. some kind of cushiony armchair. Also some kind of footstool. So, if any of you happen to see such a chair in any kind of reasonable condition lying around in hard rubbish or someones unlocked house then by all means grab it for me :).
Wednesday, March 19, 2008
Parallel Transport
Man, the ancient Chinese rocked. I didn't even know this was possible!
South Pointing Chariot
Man, the ancient Chinese rocked. I didn't even know this was possible!
South Pointing Chariot
Wednesday, March 12, 2008
Spacetime
"that same unseen power of the world which impels everyone from age 20 to 40, and from 40 to 80, impels objects inside the horizon irresistably towards the singularity."
-Wheeler etc in "the big black book", describing an objects fall into the singularity of a black hole.
He says this because once you are inside the horizon of a black hole, there exist no reference frames that are at rest relative to the singularity, i.e. no possible act of man or god can halt your fall to the end of your world line. It's a pretty intense thing to say if you consider the subtleties of it.
It made me think about something else though: The magnitude of your 4-velocity (velocity through spacetime, a combination of your regular spatial velocity and your inexorable velocity through time) is constant, in all reference frames. In fact, it is equal to the speed of light.
Consider that briefly. You are hurtling unstoppably through spacetime at the speed of light. Intense.
I think this idea makes time dilation a bit more intuitive though. In your rest frame, the one you cannot help but observe the universe from, you have no spatial velocity, so your plunge through spacetime is entirely in the time direction. Aging at the speed of light.
If you observe someone else from a frame in which they appear to be moving, some of their 4-velocity is in the spatial directions, relative to you, so their plunge through time is slower than yours. Not all their 4-velocity is devoted to time. The symmetry of the situation is an interesting, and classic, consideration; namely that from THEIR point of view time is moving more slowly for YOU. Think about it. It will definately mess with your brain.
"that same unseen power of the world which impels everyone from age 20 to 40, and from 40 to 80, impels objects inside the horizon irresistably towards the singularity."
-Wheeler etc in "the big black book", describing an objects fall into the singularity of a black hole.
He says this because once you are inside the horizon of a black hole, there exist no reference frames that are at rest relative to the singularity, i.e. no possible act of man or god can halt your fall to the end of your world line. It's a pretty intense thing to say if you consider the subtleties of it.
It made me think about something else though: The magnitude of your 4-velocity (velocity through spacetime, a combination of your regular spatial velocity and your inexorable velocity through time) is constant, in all reference frames. In fact, it is equal to the speed of light.
Consider that briefly. You are hurtling unstoppably through spacetime at the speed of light. Intense.
I think this idea makes time dilation a bit more intuitive though. In your rest frame, the one you cannot help but observe the universe from, you have no spatial velocity, so your plunge through spacetime is entirely in the time direction. Aging at the speed of light.
If you observe someone else from a frame in which they appear to be moving, some of their 4-velocity is in the spatial directions, relative to you, so their plunge through time is slower than yours. Not all their 4-velocity is devoted to time. The symmetry of the situation is an interesting, and classic, consideration; namely that from THEIR point of view time is moving more slowly for YOU. Think about it. It will definately mess with your brain.
Sunday, March 09, 2008
To England!
Got an email from some random at uni today, it was sent to all the honours students. Essentially, there is some organisation that offers Australian students scholarships to do postgraduate studies at Cambridge. They're pretty hard to get, they only give out 8, presumably in the whole of Australia. They're worth like $170,000 over the 3 years of study. Still there's a meeting so I think I might go along and get the scoop.
How random would that be? Cruise off to Cambridge to get a PhD in physics. Still, life is pretty random so who knows?
Additonally, check out these awesome "posters":
I like the idea of this one but the picture just makes no sense. Looks more like saturn.
Got an email from some random at uni today, it was sent to all the honours students. Essentially, there is some organisation that offers Australian students scholarships to do postgraduate studies at Cambridge. They're pretty hard to get, they only give out 8, presumably in the whole of Australia. They're worth like $170,000 over the 3 years of study. Still there's a meeting so I think I might go along and get the scoop.
How random would that be? Cruise off to Cambridge to get a PhD in physics. Still, life is pretty random so who knows?
Additonally, check out these awesome "posters":
I like the idea of this one but the picture just makes no sense. Looks more like saturn.
Friday, March 07, 2008
Brain...melting...
The speed of light is the same in all directions in all inertial frames
Man that's messed up. Conceptually, I think special relativity is more screwed up than the general theory. Or at least the "new" parts of GR.
E.g. If you can somehow travel faster than the speed of light, you can go backwards in time (according to some observers). The two things are in fact equivalent. If you can send signals faster than the speed of light, you can set up situations in which you receive a reply to your message before you send it. Goodbye causality. Of course this is why it may not be possible to do such things. Nuts.
The speed of light is the same in all directions in all inertial frames
Man that's messed up. Conceptually, I think special relativity is more screwed up than the general theory. Or at least the "new" parts of GR.
E.g. If you can somehow travel faster than the speed of light, you can go backwards in time (according to some observers). The two things are in fact equivalent. If you can send signals faster than the speed of light, you can set up situations in which you receive a reply to your message before you send it. Goodbye causality. Of course this is why it may not be possible to do such things. Nuts.
