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#42757 - 03/08/12 02:23 AM Re: Gravitational lensing and time travel. [Re: Bill S.]
Bill S. Offline
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Infinite stairs? Could present a problem!

I used to know a furniture mover who claimed that the ideal number of people for getting a piano upstairs was one. Heís the only person I have ever seen do it, but he didnít have infinite stairs to cope with. smile
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#43260 - 04/18/12 07:50 PM Re: Gravitational lensing and time travel. [Re: Bill S.]
Bill S. Offline
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Just returning to this thread to tie up a few loose ends.

1. Is an infinitely long cosmic string theoretically possible? If so:

2. Would its tension balance its mass so that its gravity was zero? If so:

3. How could it cause gravitational lensing?
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#43273 - 04/19/12 04:17 AM Re: Gravitational lensing and time travel. [Re: Bill S.]
Orac Offline
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In string theory yes an infinitely long is possible because the length isn't in our 3D dimensions. It's infinite to us but not from another dimension.

To understand this look at what string theory proposes the world looks like

http://members.wolfram.com/jeffb/visualization/stringtheory.shtml


What it would mean would depend what dimension the actual string length was in :-)

Of coarse you have to believe in those stringy things to buy it.
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#43292 - 04/20/12 02:35 AM Re: Gravitational lensing and time travel. [Re: Bill S.]
Bill S. Offline
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Unfortunately the video is not available here because of "rights restrictions".

Returning to cosmic strings: would it be true to say (given belief in such things) that a string would have to be of finite length in our 3 spatial dimensions in order to cause gravitational lensing?
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#43296 - 04/20/12 03:50 PM Re: Gravitational lensing and time travel. [Re: Bill S.]
Orac Offline
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Not my area of expertise but I would give a qualified I would think so because the value have to resolve mathematically which at the end of the day is what string theory is.

Basically you don't get anomolies or discontinuities they just move into other dimensions.

Thats the basic problem with string theory you can't prove or disprove it because it can describe anything as it moves stuff into an untestable dimension.


Edited by Orac (04/20/12 03:52 PM)
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#43299 - 04/20/12 07:27 PM Re: Gravitational lensing and time travel. [Re: Bill S.]
Bill S. Offline
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Quote:
Thats the basic problem with string theory you can't prove or disprove it because it can describe anything as it moves stuff into an untestable dimension.


I quite liked string theory when I first met it, but frustration in the face of its untestability doesn't help. I suppose it would be naÔve to wonder if the ultimate bits of matter and energy could be strings without necessarily involving all the other by-products.
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#43300 - 04/20/12 10:33 PM Re: Gravitational lensing and time travel. [Re: Bill S.]
Bill Offline
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Originally Posted By: Bill S.

I quite liked string theory when I first met it, but frustration in the face of its untestability doesn't help. I suppose it would be naÔve to wonder if the ultimate bits of matter and energy could be strings without necessarily involving all the other by-products.



I never did care for string theory. I heard about it and didn't pay much attention to it for a while. Then I read Brian Greene's "The Elegant Universe" and my interest took a deep dive. At that time they had been working on string theory for a long time, and there was still no way to actually attach it to the universe as we know it. They had a theory with an extremely large number of solutions, and no way to figure out if any of them would match what we see around us. And since then it hasn't improved any. The best that they can come up with is that there are an infinite number of different universes, one for each solution. And we just happen to be living in one where we are possible. That is a cop-out if I ever heard one.

One thing about it, the search for a string theory that works has led to the development of a lot of mathematical tools that work great for other areas of physics.

Bill Gill
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#43312 - 04/21/12 04:42 PM Re: Gravitational lensing and time travel. [Re: Bill S.]
Bill S. Offline
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Quote:
One thing about it, the search for a string theory that works has led to the development of a lot of mathematical tools that work great for other areas of physics.


I guess this could be part of the reason why SF has maintained its popularity.

Thinking about my last question; I suppose the other bits come in because the strings need extra dimensions in which to vibrate.
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