3441

Physics, Astronomy & Cosmology / Re: Red shift

« on: 26/11/2005 18:16:38 »

This gravitational red shift down to zero frequency is precisely what the event horizon on a black hole means ie you can't see out.  In practice zero frequency is just a nominal point.  All light and radio waves travel at the speed of light however low their frequency. The lowest frequecies used for  eletromagnetic signalling are a few cycles ber second altough the sun generates lower frequencies that are experienced as iduced power surges during electromagnetric storms.

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3442

Physics, Astronomy & Cosmology / Re: Fast hits solid - what happens?

« on: 26/11/2005 18:07:29 »

The important thing to remember is that buildings, like planes are mostly empty space (windows, rooms etc) and not concrete blocks and both collapse under violent forces.  We have all seen many times what happens

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3443

Physics, Astronomy & Cosmology / Re: Could spin account for an expanding Universe?

« on: 26/11/2005 17:59:14 »

To give my answer to your question ukmicky,  My guess is that the universe has the maximum amount of angular momentum that it can have altough that could reperesent a very slow rate of net rotation based on the current size of the universe.  Bearing in mind that if inflationary cosmologies apply we can only see a tiny part of our universe.  AFIK the only way we could detect this would be to detect a tiny net centrifugal force. but again my guess is that this will be closely balanced by the net gravitational force both of which can only be estimated by very accurate meaurements of the motions of a very great many galaxies over a vast region.

It is very easy to forget about the effect of angular momentum and I feel that some of the scientists who glibly talk about the collapse of material iside a black hole to a singularity have forgotten this.  The classic picture of a black hole that is usually given is one that is not rotating and i think that because of the conservation of angulsr momentum it is almost impossible to make a black hole that ids not rotating at pretty close to the maximum speed that it can rotate.  A rotating black hole is a much more complex stricture than a non rotating one and I am only just starting to get my brain round what it is like.

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3444

Physics, Astronomy & Cosmology / Re: Could spin account for an expanding Universe?

« on: 26/11/2005 17:15:56 »

Angular momentum (another word used to desgribe rotation or spin) is probably the most fundamental feature of our universe.  At least as fundamental as gravity.  it is in fact the reason why the universe does not collapse back into nothingness!  In any closed system, like energy, angular momentum is conserved so if a spinning object be it gas cloud or ballerina as it contracts so it spins faster to maintain the angular momentum.  

It is interesting to note that Planck's conatant has the dimensions of angular momentum and most particle interections are described in terms of exchanges of angular momentum.

The angular momentum of the earth in its orbit about the sun is what stops it falliing into the sun under the effect of its gravity.  

In exactly the same way, it is the angular momentum of an electron around a proton in a hydrogen atom stops it falling into the proton under the effect of the attractive electrical forces.

Now for an intersting fact about out solar system.  Most of the angular momentum in the solar system is in the panets if all the planets including their angular momentum were pushed into the sun the mass and material content would not change very much but the sun would be rotating so fast that it would fall apart!  That is, forming planets is one of the ways a gass cloud sheds its angular momentum to form a star!

in exactly the same way a free electron must shed angular momentum by radiating electromagnetic waves when it joins a proton to form a hydrogen atom.

Pauses for breath :-)

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3445

Physics, Astronomy & Cosmology / Re: Could spin account for an expanding Universe?

« on: 26/11/2005 16:54:06 »

There is clearly turbulence in the universe at all levels but whether the universe as a whole is rotating is very difficult to measure because we are inside of it and can't see out!

However this is a very interesting question and worthy of some thought.

as this is my first post on this forum I will post now before adding more.

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