Eternity

[Le Chat]

Sometimes I muse on this....
If we sent a rocket into space with an everlasting power supply and tracking, presumably it would just go on forever and ever as there is no end.
I just can't imaging 'no end' to anything....but if there was an end, what would there be? A wall? What would be after that?
Can anyone make sense of this?

[Old_Geezer]

If space curves then you can have a closed system, there need be no wall, you just find yourself back where you started eventually. It is the only thing that makes (relative) sense to me. However the next question is whether your rocket can go fast enough to compensate for expanding space. But I guess it is a theoretical rocket so that's no problem.

[scowie]

The universe isnt "known" to have had a beginning. It is thought to have had one (mainly due to scientific consensus having being led astray by the ideas of a belgian priest and a swiss patent clerk). You may find these two documentaries enlightening:

http://video.google.c...d=1966820922322808100
http://video.google.c...=-2827896363014586265

Infinite space makes more sense than curved space in my mind.

[jake-the-peg]

Oh dear Scowie!

You don't believe that video do you?

I'm sure infinite space does make more sense to you - there's just one problem - it doesn't fit the facts - not just one or two observations but hundreds.

It was first demonstrated by light from a star getting bent around the sun during an eclipse - You just can't explain that without bent space.

We see double images of galaxies being bent around other massive galaxies.

Moreover SatNavs need general relativity to work correctly - without Albert Einstein they would lead you astray!

You really need to be careful about believing what you see on the internet.

[jno]

they lead people astray anyway

http://www.itv.com/ne...esex-drowns-in-flood/

I'm not sure it's fair to blame the Swiss patent office, though

[Old_Geezer]

If it leads folk astray it is more likely to be down to inaccurate map data than poor positioning from the satellites. Ultimately they are just a tool, one needs a little thought applied when using them.

[jake-the-peg]

I could cite many other examples where general relativity has been shown to be correct.

For example the orbit of mercury can't be correctly calculated with flat Newtonian space - but that is a bit arcane for many people to relate to.

If you say that their SatNavs need to take account of relativity that's something people can relate to

[scowie]

Light being affected by gravity doesnt mean that space must bend. The bending of space might be a convienient analogy but that's all it is - it has no physical reality. I am not saying einsteins relativity equations are wrong, just the unnecessary crazy ideas that are attributed to them. The idea that mass increases with velocity is another one. The fact that a charged particle becomes increasingly harder to accelerate at relativistic velocities doesn't necessarily mean that the particle's mass is increasing. Read this: http://www.alternativ.../RelativisticMass.htm

In fact, reading the whole of that site may open your eyes somewhat.

[jake-the-peg]

Scowie - ths doesn't help your argument

Relativistic mass increase is a function of the rest mass of a particle.

Photons are massless and hence this is irrelevant.

The experiments show light being affected by Gravitation - if you don't bend space you have to revise Newtons law of Gravitation

What you'll end up with is effectively Einstein's picture of Gravity

Besides this the link you've provided is proveably wrong

The reltivistic mass increase is different between protons and electrons - both have the same charge but very different masses.

For this to be the case the charge change would have to be dependant on the mass of the particle.

Also abeam of charged particles in a collider tend to repell each other and have to be refocussed because of their electric charge - if this electric charge reduced so would the need to refocus them (which is not observed).

[scowie]

General relativity *is* a revision of newton's laws of gravitation.

I don't believe a particle's charge reduces as it's speed increases, but rather an electric field propagates at speed c with respect to it's source so as a particle is accelerated to relativistic speeds it is effectively catching up with the field of the particle accelerator and therefore has less force exerted on it, as in the wind tunnel analogy. The electric field of the particle accelerator would appear to get weaker from the particle's perspective but since there is little velocity difference between each particle in the stream, their relative charges would remain the same.

Btw, i'm not convinced that photons are actually massless either, or that c is the speed limit of the universe.

[jake-the-peg]

And so why when subatomic particles strike targets do resultant neutral particles never exceed c then? Z bosons for example?

http://tri-lab.lanl.g...ced-and-reconstructed

They've sure got enough energy to do so!

[jomifl]

Markrae, just a couple of points, It is not possible to escape from the earth's gravitational field since it extends to infinity (wherever that is), it is possible to have 'escape velocity' which means that you have enough velocity to keep moving away from the earth. This however is not enough as you have to have enough velocty to 'escape' from the sun, the complete solar system and our galaxy.

[Johnysid]

If you have the patience you should probably start here:

http://en.wikibooks.o...ki/Special_Relativity

This is a simple guide to the idea of a four dimensional universe. It does not make your brain ache provided you are prepared to learn something new.

Beginners have a problem with "time" in relativity because they are taught that time as a separation between events (a sort of distance) is the same as change (the succession of events). Relativity only tackles the first sort of "time". The second sort of time, change, has not been properly explained by physics.

[Johnysid]

ps: I would recommend going straight to the pdf version:

http://upload.wikimed..._Relativity_V2.11.pdf

rather than going through all the Wikibook links.

[scowie]

No, they sure *dont* have the energy to do so. Since the mass of the Z boson is 91.2 GeV/c² and those collisions had energies of 2.76 GeV, those particles are obviously only gonna have a fraction of the speed of light.