The Speed of "Light"

Sir Ulli
Sir Ulli
Joined: 18 Jan 05
Posts: 121
Credit: 104603
RAC: 0

more links, donst know if

more links, donst know if someone post this before


The twin paradox

Resolving the twin paradox of Special Relativity using animations


The Einstein-Minkowski Spacetime:

The Einstein Principle of Relativity


Borrowed Time: Interview with Michio Kaku

A theoretical physicist contemplates the plausibility of time travel

Greetings from Germany NRW
Ulli
[img]http://boinc.mundayweb.com/one/stats.php?userID=380 [/img]

Dennis
Dennis
Joined: 19 Feb 05
Posts: 51
Credit: 4459
RAC: 0

>> > Resolving the twin

Message 6276 in response to message 6275

>>
> Resolving the twin paradox of Special Relativity using animations
>
>
> The Einstein-Minkowski Spacetime:

>
> The Einstein Principle of Relativity
>
The problem with all these is that they ust move the problem from one area to another. Yes, general relativity can help you see why one ages and one does not by saying the spaceship feels acceleration and the earth does not. However, the problem is then why is the frame of reference of the distance stars so special. Is there a preferred frame of reference or not. What about comparing the case when the rocket stays put and the earth AND the entire universe moves and accelerates? There is something special about the reference frames of the distant stars. That brings up the Mach principle, which has never really been fully addressed even in general relativity. It is at the heart of inertia.

And if that is not enough what about a rotating frame compared to the frame of distant stars – after all angular momentum doesn’t really have to be conserved in GR since it is not a true tensor but only a pseudo-tensor. These little pulsars we are looking for are rotating – or are they stationary and it is the universe that is rotating. (I believe the first and the Mach principle)

Have fun,
Dennis

Sir Ulli
Sir Ulli
Joined: 18 Jan 05
Posts: 121
Credit: 104603
RAC: 0

more Info and more links

more Info and more links


Fermi paradox

The Fermi paradox is a paradox proposed by physicist Enrico Fermi that questions the probability of finding intelligent extraterrestrial life. More specifically, it deals with attempts to answer one of the most profound questions of all time: "Are we (human beings) the only technologically advanced civilization in the Universe?". The paradox was formulated in response to the Drake equation for estimating the number of extraterrestrial civilizations with which we might come in contact. Subject to the values inserted into this formula, the Drake equation seems to imply that we should not expect such contact to be extremely rare.


Fermi's Paradox III: Zookeepers, Alien Visitors, Or Simple Life; How Can We Explain Our Isolation

and for the speziell people here who are good on physics


Protosimplex – Ideas of Burkhard Heim

btw this is really heavy Stuff...

Greetings from Germany NRW
Ulli
[img]http://boinc.mundayweb.com/one/stats.php?userID=380 [/img]

Byron Leigh Hatch @ team Carl Sagan
Byron Leigh Hat...
Joined: 18 Jan 05
Posts: 116
Credit: 2037008
RAC: 0

Hi Ulli , ___ thanks very

Message 6278 in response to message 6277

Hi Ulli , ___ thanks very much for those science links
Best wishes to Ulli in Germany __ from byron in Canada

My Very Best wishes to everyone ......... and keep on crunching :)

friendly and respectful
byron ... [/url] _ Earth Flag

Nereid
Nereid
Joined: 9 Feb 05
Posts: 79
Credit: 925034
RAC: 0

Much confusion and mixing of

Much confusion and mixing of ideas here ...
String theory: when there was nothing else for physicists to work on, they agreed that String theory (now M-Theory) was worth the effort. But is it science? Can it (really) be tested (even in principle)?

The best tests of the constancy of G, e, c, ... have all come up blank (within the experimental error margin). There are several tests of all of these which *appear* to show variation (with time), but if you look closely, they've all got problems.

Beware press releases! It may be cool to say something that gets you some coverage in the press, but whether your research results are as strong as the claims the press makes (or hint at) is quite another matter!

Now that c is part of the definition of length, we need to be very, very careful about experiments/observations which claim it may have changed over cosmological time.

debugas
debugas
Joined: 11 Nov 04
Posts: 170
Credit: 77331
RAC: 0

Drake equation has nothing to

Message 6280 in response to message 6279

Drake equation has nothing to do with real science.
Equation in which its elements cannot be measured but instead continuous speculastions are going on about their estimated values , such equation has no real meaning to science but is a speculative discussion. Even though pseudo-scientists can reach a consensus in their estimates of the equation elemets values, real science is not about consensus - real science is about plain clear facts.

I really feel that real science is in danger being attacked by all sorts of sharlatans (pseudo-scientists) who claim the scientific society reach a consensus on that and that (take a look for example on global warming discussions, europe now started trading in CO2 gas emitions but it is well known that there are many other gases that pose much more serious effect on global warming than CO2)

debugas
debugas
Joined: 11 Nov 04
Posts: 170
Credit: 77331
RAC: 0

Answer to Dennis' twins

Message 6281 in response to message 6280

Answer to Dennis' twins paradox question can be found here.
http://users.chariot.net.au/~gmarts/timewarp.htm
Read it carefully and you will grasp the true meaning of relativity

Shortly speaking here is a quote that can shine the light on why one twin becomes younger than other:

"The twin paradox is one of the most often described aspects of special relativity. Unfortunately, it is also one of the most poorly explained. The heart of the paradox is that relativity requires that each twin observe the other's clock as running slower than normal. But since the twins age differently, one of them must have observed the other to have progressed more rapidly than normal through time.

Some texts simply state that the discrepancy is caused because special relativity doesn't handle accelerated frames of reference, and one of the twins is accelerated (3 or 4 times). Others go a little farther with the following explanation:

Each of the twins sees the other's clock as running slow when they are moving apart and fast when they are moving together (due to the Doppler shift). The twin in the rocket sees the transition occurring the instant the rocket turns around and thus sees the Earthbound clock running slow during the first half of the journey and fast during the last half. But the twin on Earth doesn't see the change in direction until well past the halfway point. This is due to the fact that it takes a long time for the turnaround to be seen because it is so far away. Thus the twin on Earth sees the clock on the rocket as running slow for more than half of the duration and fast for less than half. This asymmetry leads to the discrepancy in the twin's ages.

While this is technically accurate, its rather unsatisfying. For one thing, we don't observe similar time discrepancies when dealing with sub-light (e.g. sound) Doppler shifts. For another, it doesn't explain when the twin in the rocket observes the other twin to be moving too fast in time. Relativity indicates that during both the outbound trip and inbound trip, the twin in the rocket must observe Earth's clocks as running slow. "

One more comment. While reading that article most crusial realisation i got was that in relativity books authors rarely make distinction between what observer A sees about observer B and what he calculates as beeing other's observer reality (what is there now)
In many books they simply write that each twin sees other's clock to run slowly. this is not true, they calculate each others clock to run slowly and what they actually see is affected by doppler shift.

When you take a look at sky and see a star eight light years away you see it as it was 8 years ago but you calculate it to has already passed those 8 years and be simultanious with your time but just 8 light years away

what you see is real but what you estimate is still not a reality but is a conditioned assumptions about what there now should be . You can't be sure star is still there now until you wait for 8 years and see that it really was (and did not explode for example or started accelerating and moved to 9 ly away). In other words there now (your reality extended into far away from you) does not really exist until you start to observe it later when light arrives, nevertheless many books on relativity keep on talking about this there now reality and thus mislead the reader about what relativity is all about. Our intuition requires us to estimate the world as simultanious 3D-plane of space (all those space points there now, there now), but it simply does not exist in that way, hence appear the paradoxes (simply because we try to use old-fashioned notions where they are not applicable).
One more example - if mass increase with speed why don't elementary particles become black-holes in accelerators ? the answer is the notion of mass is badly applied in the question, mass is not a scalar but a 4-D vector and rest-mass does not increase with speeding up. What's the point in misleading students talking about mass increase with speed ? better start talking about mass as 4D vector from the very start so no confusions arise

Dr. Roi
Dr. Roi
Joined: 11 Feb 05
Posts: 1
Credit: 9961
RAC: 0

"Nothing like some numbers in

Message 6282 in response to message 6259

"Nothing like some numbers in a case like this! Thanks
It would be very difficult for the constant C (the speed of light in a
vacuum)
to change without some major revisions on how we understand the universe
to
work.

Take E = MC^2 for example. This formula shows that matter can be
converted in
energy and back based on a set ratio (C^2). Now suppose C could change,
what
would happen...

For simplicities sake, lets set C=1. At some period in the past this
mass of
1 is converted into energy...

E=MC^2
E=M(1^2)
E=M*1
E=1*1
E=1

Okay, time passes and now C= .5 and the energy of 1 is converted back to
mass
E = MC^2
E/(C^2) = M
1/(.5*.5) = M
1/.25 = M
4 = M

We started out with a mass of 1 and ended up with a mass of 4... so
where'd
the extra mass come from? This just defies everything we understand."

Not only that but the very nature of the Verse would be changed, the stars would not burn at their present rate if at all, and the Verse would not exist as we know it, nor would we be here to observe it. If you change C then E and M must change as well. Decreasing C would cause E to drop, hence no stars. If C were greater than it is at present the Verse would have burned out long ago.

gravywavy
gravywavy
Joined: 22 Jan 05
Posts: 392
Credit: 68962
RAC: 0

> We started out with a mass

Message 6283 in response to message 6282

> We started out with a mass of 1 and ended up with a mass of 4... so
> where'd
> the extra mass come from? This just defies everything we understand."

Energy is conserved in an inertial frame.

The Universe as a whole is not an inertial frame, as the scale of the universe is changing with time. Therefore we do not expect the total energy of the universe to be conserved.

Think about this. A long time ago there was a big bang, and it got very hot. A few hundred thousand years later space became transparent - this was when the electrons that were whizzing round finally joined up with the protons an deuterons to make the first Hydrogen atoms. (With a small smattering of Helium to add variety). Before that the free electrons and the charged nuclei were a glowing pasma, a nice cherry red colour and the temperature was around 3000 K.

Now when we look at the sky we see microwaves coming from all directions. Those nice cherry red photons (typical of a blck body at 3000 K) have stretched to become microwaves.

But there are the same number of photons now as then (minus the few that already got absorbed, but the whole point of the 3K background is that almost all of this primordial radiation did not get absorbed).

Each photon has about 1000 th the mass/energy as it did back then. Where did the energy go? It didn't go anywhere, the photon have not reacted. The mistake is in applying conservation of energy, which can only apply in an inertial frame, to the whole universe which is not such a frame.

Look at any one photon in the frame of reference extended from the matter around it when it started on its 10^10 year journey and it has kept the same energy, it is still cherry red. But shift to a different frame and it is not.

True, if c varied with time, even that amount of equality would be broken. But it has to be said that such tersts have never been done. Energy is conserved in experiments lasting a few minutes, or years, but maybe not over the life of the universe.

> Not only that but the very nature of the Verse would be changed, the stars
> would not burn at their present rate if at all, and the Verse would not exist
> as we know it, nor would we be here to observe it. If you change C then E and
> M must change as well. Decreasing C would cause E to drop, hence no stars.
> If C were greater than it is at present the Verse would have burned out long
> ago.

Except that, if c really is slowly varying, we'd be dependent on *that* fact to be here, and presumably we would not be here in a constant c universe.

In short, we cannot rely on intuition to extend the knowledge of a civilization (6000 yrs) over a period two million times longer. In principle any of our familiar constants could actually be 'constants', slowly varying over cosmological time.

What we can do is insist that the changes are slow enough that we would not expect to see the difference. I am sure that the people who made up this model thought of that.

We can also work out tests that do depend on the early values of c (or G, or whatver other constant is under attack) and see if there are effects we'd expect to be different nowadays. Like the temperature of the microwave backgound; like the relative amount of Hydrogen and Heliuum in intergalactic space, and so on.

So far the jury is out, but most physicists in the meantime prefer to think that the constants really are constant. Not because it has been proved, but because we are reluctant to add any more complexity than the universe forces upon us.

~~

~~gravywavy

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.