Magnetism

Matt Gregory · Post by **Matt Gregory** » Wed Mar 21, 2007 11:57 pm

It says here in A Brief History of Time that if gravity was a force, it would have to travel at or less than the speed of light, so that's why Einstein came up with the theory of warped space. But does that mean that magnetism is a force and therefore it travels at or less than the speed of light?

Elizabeth Isabelle · Post by **Elizabeth Isabelle** » Thu Mar 22, 2007 12:14 am

That does not make any sense. A force acts, it does not travel. Traveling is an effect of a force. Light travels as a result of the momentum of the photons - momentum being the force. (technically, force is the rate of change of the momentum, but you get the idea)
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Matt Gregory · Post by **Matt Gregory** » Thu Mar 22, 2007 12:22 am

I know it sounds nuts but that's what this book says. It says it's required by the special theory of relativity that no thing in the universe can affect anything else at a distance faster than the speed of light can travel from it.

Elizabeth Isabelle · Post by **Elizabeth Isabelle** » Thu Mar 22, 2007 12:27 am

I don't doubt that's what the book says (I read it a number of years ago), but Einstein had some flaws in his work.

Matt Gregory · Post by **Matt Gregory** » Thu Mar 22, 2007 12:30 am

Like what?

Leyla Shen · Post by **Leyla Shen** » Thu Mar 22, 2007 12:40 am

Doesn't sound quite right to me. What page, Matt?

Matt Gregory · Post by **Matt Gregory** » Thu Mar 22, 2007 12:51 am

pp 29-30

The special theory of relativity was very successful in explaining that the speed of light appears the same to all observers (as shown by the Michelson-Morley experiment) and in describing what happens when things move at speeds close to the speed of light. However, it was inconsistent with the Newtonian theory of gravity, which said that objects attracted each other with a force that depended on the distance between them. This meant that if one moved one of the objects, the force on the other one would change instantaneously. Or in other words, gravitational effects should travel with infinite velocity, instead of at or below the speed of light, as the special theory of relativity required. Einstein made a number of unsuccessful attempts between 1908 and 1914 to find a theory of gravity that was consistent with special relativity. Finally, in 1915, he proposed what we now call the general theory of relativity.

Einstein made the revolutionary suggestion that gravity is not a force like other forces, but is a consequence of the fact that space-time is not flat, as had been previously assumed: it is curved, or "warped," by the distribution of mass and energy in it.

DHodges · Post by **DHodges** » Thu Mar 22, 2007 1:05 am

Matt Gregory wrote: But does that mean that magnetism is a force and therefore it travels at or less than the speed of light?

Yes, the electro-magnetic force (e.g., the creation or movement of a magnetic field) is limited to light speed.

Leyla Shen · Post by **Leyla Shen** » Thu Mar 22, 2007 1:20 am

I was still stuck on the first part of your question, Matt--damn you Hodges. The term "curved" or "warped" space always throws me. That's what happens to phenomena when the maths don't add up!

Elizabeth Isabelle · Post by **Elizabeth Isabelle** » Thu Mar 22, 2007 1:38 am

A force is not a speed, it is a strength. They have only just been able to capture a single photon in a box (I think for a seventh of a second), so I know they have not been able to test the speed of a photon powered by magnetism.

I know it is currently believed in the scientific community that absolutely everything is limited by the speed of light, but the scientific community of days past also once firmly believed that Earth was flat.
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Leyla Shen · Post by **Leyla Shen** » Thu Mar 22, 2007 3:03 am

Elizabeth:

Yes, but as we all know, science is ever-evolving and these definitions donâ€™t just pop out of nowhere. If you accept a finite beginning to the universe like The Big Bang crew have, underpinning such a beginning of the finite universe (the Big Bang event itself), was a time when the mass/density of the universe was infinite--including in no particular form, everything we see and extrapolate today. This is the theory--based on the maths, of course. So, then this infinitely dense universe explodes and expands outwards (according to Hubble's observation) with a corresponding decrease in mass per unit as it does so. Hence, all our current scientific theories.

From that, one can see how force/strength and speed cannot actually be separated.

Whatâ€™s your theory for separating them?

Philosophaster · Post by **Philosophaster** » Thu Mar 22, 2007 6:39 am

Scientists have not measured the speed of light in an experiment, or at least not definitively. Two scientists claim to have gotten a measurement of about the speed of light, but this is disputed.

It is worthwhile to note that relativity theory also problematizes what it means for two events to be "simultaneous," since it dispenses with the idea of "absolute time."

Matt Gregory · Post by **Matt Gregory** » Thu Mar 22, 2007 7:13 am

Elizabeth Isabelle wrote:A force is not a speed, it is a strength.

I was asking about the speed of change in a magnetic field. If you created a magnetic field by turning on a huge electromagnet, the growth of the field would be limited to light speed.

Matt Gregory · Post by **Matt Gregory** » Thu Mar 22, 2007 7:40 am

Hi Philosophaster,

It is worthwhile to note that relativity theory also problematizes what it means for two events to be "simultaneous," since it dispenses with the idea of "absolute time."

I don't even believe in physical time, only change. I think everything shares the same present, but everything changes at its own speed according to the theory of relativity. The twin in the rocketship changes more slowly than the twin on Earth, but they always share the same present.

Dan Rowden · Post by **Dan Rowden** » Thu Mar 22, 2007 8:34 am

This isn't necessarily germaine, but I got a laugh out of it. Listen to this short podcast of Paul Davies talking about time travel. I laughed out load because I found it ridiculous. What do the rest of you think?

Time Travel

Leyla Shen · Post by **Leyla Shen** » Thu Mar 22, 2007 9:21 am

Oh, for crying out loud!

(Einstein was a pacifist, too, by the way.)

Ignorant Carl G Arse · Wed Apr 04, 2007 8:31 am

Its the same force that attacts my hand to stroke my genius...

MindExpansion · Post by **MindExpansion** » Sat Apr 07, 2007 3:15 pm

Why doesn't someone delete posts like the above.

MindExpansion · Post by **MindExpansion** » Sat Apr 07, 2007 3:16 pm

*such as the above.

GENIUS FORUMS

Magnetism

Magnetism

Re: Magnetism

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