Faster than the speed of light

  • Thread starter Jack
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  • #26
neutroncount
Originally posted by Jack
OK, now for my next stupid question-

If time slows down to a stop as you approach the speed of light then how can light travel?
Because GR only applies to objects with rest mass. Photons have no rest mass. They only impart momentum when striking an object; they have have no real mass. By definition a photon cannot have mass. If it did, you could slow it down below its c velocity in a vacuum (a big no-no). Also, there is no time that a photon is accelerating (a GR requirement). It's at c from its creation until you cause it to interact with some medium. That's not to say that you can't modify light in a vacuum. Gravitational blueshifting is an example of wavelength shifting. But it still continues to travel at c.
 
  • #27
marcus
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Originally posted by wimms
I was confused by Hurkyl's example that you agreed with. I did read it as: if we have object that was relativistically receeding at 0.7c, and it was in point of space that receeded from us at 0.5c due to expansion, back then, then we'll be able to see that light although in total it was receeding at 1.2c. I just exagerated that to infinity, duh. How about 0.99c + 0.99c?

.
Hi wimms! I have been away and just got back to board and saw your post, or would have replied sooner.

I tried just now to answer but got off on the wrong foot.
also too many demands on time this morning
had to erase. will get back to this.
 
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  • #28
Hurkyl
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You might be interested in the formulas and calculating it yourself instead of resorting to the Javascript online calculator.
I guess I should have phrased my inquiry better hehe, though I got the answer I wanted: mainly I just wanted to know if the rate of recession is computed between where we are now and where the quasar is "now". (instead of when it was observed) I imagine from your presentation that the actual formula is probably too complicated to be worth studying with my present level of knowledge of GR.
 
  • #29
marcus
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when and if I find anything along those lines I will
send it to you PM

the basic question in my mind is, how does Wright's
online calculator work----how does it get from the
redshift z you put in to the current distance to the object
which it give you back.

maybe to your eyes the calculation is not so bad
in anycase no harm in your taking a look and making
your own assessment. I know I am really lazy and would
rather just use the calculator---but I am still curious how
the calculation goes

it may be awhile before I come across it but I will keep
an eye out. also if you happen upon it before I do I'd appreciate a pointer to the information.
 
  • #30
When you say no speeds can be faster than light be sure to specify that it is in the context of Special Relativity. It is true in that context and not true in the universe at large of General Relativity.
Could you please elaborate it by using an example?

I think nothing can travel faster than light. Although quasars have great redshift, but it doesn't mean they are travelling >c.
If we use the classical formula for doppler shift,
v/c = d[lamb]/[lamb]0=z,
we can get something like 4z or 5z, and v>c.
But if we apply the relativistic doppler formula,
v/c = [(z+1)2-1]/[(z+1)2+1],
v/c always smaller than 1 in this case.

Since quasars move in high velocity, relativistic doppler formula should be applied, which implies that quasars can't travel faster than light.
 
  • #31
Originally posted by Hurkyl
You sure on that? If, for instance, we start with an object receding special relativistically at a speed of 0.7 c, and then add in a 0.5 c recession due to the expansion of space, the light from the object should have no problem reaching us, although the object is receeding at 1.2 c.
What's the difference between moving special relativistically and moving due to the expansion of space?
 
  • #32
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Since light from very distant objects cannot reach us, there must be a certain horizon in the universe, like the event horizon of a blackhole. And this horizon emits thermal radiation, similiar to black holes, and they are now observed as small variation in the temperature of the cosmic background.[URL [Broken] a site on hawkig radiation[/U

Is there an equivalent of the sonic boom for light?

Physicskid[zz)]
 
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  • #33
marcus
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Originally posted by AndersHermansson
What's the difference between moving special relativistically and moving due to the expansion of space?
Hello Anders, I just now saw your post. (forgot to check this thread for a while). Hurkyl proposed looking at an object in a part of space receding 0.5 c from us, where the object also has its own individual speed (relative to the CMB) of 0.7c.

The important thing to realize is that the 4D coordinates of SR do not fit space at large scale. So the object as no "special relativity" speed relative to us. It simply is not defined. SR type speeds are defined only for objects at the same point or in the same local coordinate chart.

The metric used in cosmology (socalled RW metric) is defined with reference to observers stationary with respect to the CMB or, as cosmologists say, w/rt the Hubble flow (the expansion of the universe). The RW, or RobertsonWalker, metric can handle the speed Hurkyl mentioned. The combined recession speed, the rate of change in RW distance, is meaningful and equal to 1.2 c.

The RW distance, measured at the present moment, is also called the "comoving distance" or the Hubble-law distance because it is the gauge of distance that works in the well-known Hubble law:

v = H0 D.

The v in the Hubble law is the present rate of change of the RW distance, which is D.

The H0 parameter is, by definition, the present value of

at/a

where a(t) is a numerical valued function of time used to define the RW distance----a distance scale measured from the standpoint of observers at rest with respect to the expansion of space---ie. w/rt the CMB.

a(t) is defined because, in cosmology, all stationary observers everywhere in the universe can have the same time axis---they can have synchronized clocks---essentially one clock for everybody. So there is one scale-function a(t) evolving with time, for everybody.

This is radically different from the picture you get in SR. It is very much a General Relativity picture, by contrast to the local SR picture.

The basic trouble with SR, why it cant be used except locally around a point where there is not much curvature, is that
SR does not allow for space to expand.
The Minkowski 4D coordinates of Special Relativity are rigid and do not let space expand, so these coordinates "fit" the world only in small local patches or local "charts".

this is why the speed of recession of distant objects is not defined in SR coordinates and all that "nothing can exceed the speed of light" business simply does not apply.

Hope this adequately covers the question. the distinction between local SR distance and the real physical distance with the metric is important to make. Please ask further if not clear. I can get you some links to, for instance, Eric Linder's Cosmology Overview (which covers the RW metric) and New Wright's tutorial, which discusses the RW distance and three alternative ideas of distance (angular size, luminosity, light-travel-time). Also other people may want to take a shot at this and you will get several viewpoints.
 
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  • #34
marcus
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Originally posted by physicskid
Since light from very distant objects cannot reach us, there must be a certain horizon in the universe, like the event horizon of a blackhole. And this horizon emits thermal radiation, similiar to black holes, and they are now observed as small variation in the temperature of the cosmic background.[URL [Broken] a site on hawkig radiation

Is there an equivalent of the sonic boom for light?

Physicskid[zz)]
You have a link here to the Usenet Physics FAQ about cerenkov radiation. The Physics FAQ is a great web resource! It also has something on Hawking radiation. Here is a quote from the Usenet FAQ on Hawking radiation:

(John Baez writes)
"...How does this work? Well, you'll find Hawking radiation explained this way in a lot of "pop-science" treatments:

Virtual particle pairs are constantly being created near the horizon of the black hole, as they are everywhere. Normally, they are created as a particle-antiparticle pair and they quickly annihilate each other. But near the horizon of a black hole, it's possible for one to fall in before the annihilation can happen, in which case the other one escapes as Hawking radiation.
In fact this argument also does not correspond in any clear way to the actual computation. Or at least I've never seen how the standard computation can be transmuted into one involving virtual particles sneaking over the horizon, and in the last talk I was at on this it was emphasized that nobody has ever worked out a "local" description of Hawking radiation in terms of stuff like this happening at the horizon..."

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/hawking.html

The widely-believed picture of one virtual partner falling in and the other getting away (you give a link to an animation of this idea) may be too simple to explain the actual Hawking radiation.
Do you have a link that, for instance, derives the Hawking temperature using this model?

An interesting question is---why is the Hawking temperature of the black hole given by this formula?

kTHawking = (1/8piM)(hbar c2/G)

In the Hawking formula for the temperature, M is the mass of the black hole, k is Boltzmann's constant, and hbar and c are the usual hbar and c.

The formula, derived in Hawking's orig. 1975 paper, does not seem to come from this picture of "one partner falling in and the other getting away". The formula, however, it what seems to matter because it predicts the temperature of the radiation.

I would like to understand the temperature formula better. Have you found any website that derives it?
 
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  • #35
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Hawking radiation[zz)]

Yes! That's definetely a resourceful site for physics fans who think
they know a lot on physics.

To someone far from the black hole, the escaping particles would appear to have been radiated by the black hole. The spectrum of the black hole is exactly what we would expect from a hot body, with a temp. proportional to the gravitational field on the event horizon.

taken from Stephen Hawking's <<The Universe in a Nutshell>>
The temp. of a black hole depends on its mass. So a smaller black hole would be hotter.
 
  • #36
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I don't want to sidetrack this discussion but could someone please give me a phonetic pronunciation of "João Magueijo"?
 
  • #37
Sciencegenius
In relation to Hawking Radiation does a black hole have to give up the exact amount of energy/mass equal to the energy/mass of the particle being made "real" in accordance with E=MC^2 or is there something else to be considered?[?]
 
  • #38
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Originally posted by Sciencegenius
In relation to Hawking Radiation does a black hole have to give up the exact amount of energy/mass equal to the energy/mass of the particle being made "real" in accordance with E=MC^2 or is there something else to be considered?[?]
Science genius,
These virtual particles are a anti-particle pair. They are created out of nothingness and annihilate each other quickly before interacting with other particles. Their creation are explained by the http://physics.hallym.ac.kr/education/hep/adventure/virtual.html [Broken]. Please find out more on quantum mechanics and quantum physics on your own. (all revolving around the planck's constant h).

Hope you'd be able understand these theories. Ask for help if you have any difficulties.[zz)]
 
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  • #39
Sciencegenius
Yes but I mean in the case of Hawking radiation when they are unable to anhilliate each other does the black hole have to do any "work" in relation to my question.
 
  • #40
477
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Originally posted by Sciencegenius
In relation to Hawking Radiation does a black hole have to give up the exact amount of energy/mass equal to the energy/mass of the particle being made "real" in accordance with E=MC^2 or is there something else to be considered?[?]
becuase of the well known Law of Energy Conservation, the outflow of energy created by the virtual particle being made into a "real particle" (light, i guess) is balanced with an inflow of energy into the black hole, and thus (in time) dissolving the black hole. is this what you were asking?
 
  • #41
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Imagine your being being completely made up of consciousness and "thought energy" is what propelled you throughout the universe.

You can then instantly appear anywhere at anytime. As long as your conscious mind is there, then you are. What prevents us from doing this in the physical world, is physical matter.

However, is human thought not faster then light? I can right now think of myself dancing around on the surface of pluto, and I did that within a split second, how fast does it take light to get to Pluto from earth? Yet my consciousness was there instantly.
 
  • #42
neutroncount
Originally posted by Ploegman
Imagine your being being completely made up of consciousness and "thought energy" is what propelled you throughout the universe.

You can then instantly appear anywhere at anytime. As long as your conscious mind is there, then you are. What prevents us from doing this in the physical world, is physical matter.

However, is human thought not faster then light? I can right now think of myself dancing around on the surface of pluto, and I did that within a split second, how fast does it take light to get to Pluto from earth? Yet my consciousness was there instantly.
That's the stupidest thing I've ever heard. When I imagine myself someone else, that's just what it is. IMAGINING! My brain can visualize and create/recreate images, sounds and feelings because of our memories that are triggered from chemical reactions within our brain. Nothing at all is traveling faster than light. I hate to say it folks but our brain is just a peice of meat. A thinking peice of meat but no less a peice of meat. And I have a feeling you're not using yours enough.
 
  • #43
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Originally posted by physicskid
Since light from very distant objects cannot reach us, there must be a certain horizon in the universe, like the event horizon of a blackhole. And this horizon emits thermal radiation, similiar to black holes, and they are now observed as small variation in the temperature of the cosmic background.
The mass of the galaxies outside the horizon should decrease too, since the antiparticles 'disolves' them.

But the Milky Way is also outside the horizon of another very distant galaxy travelling FTL speed relative to us, so we should receive antiparticles from it too! So there is an equal exchange of particles between us and the distant galaxy. These anti-particles pair annihilate each other again. So the law of energy conservation is obeyed. [zz)]
 
  • #44
I thought the speed of light is the speed of light in a vacuum. Isn't there some kind of theory explaining something moving faster than the speed of light (for a vacuum) in a medium. Karismov theory or something like that?
 
  • #45
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FTL Quasars

I am always leary of those that post "Absolute Statements". I decided to join because I saw this thread. I have never seen a discussion of FTL that took this direction and seperated expansion from relavistic velocity. I like that and particularily since the factor 2c fits my own view as well.

The following link claims to provide mathematical proof that nothing goes FTL but I don't accept what is being done. That is not to argue that the mathematics are not consistant but only that they are inappropriate attempts to force reality to conform to the preconcieved idea of Relativity. We should infact be looking for alternative explanations which include observation without manipulation.

The fastest Quasar velocity that I have seen recorded is 5,200 c.

That is a traverse "observed" motion but using the mathematics in the following link they claim it is only an illusion and it is really <c.

I don't buy it. "Y" is the observed traverse velocity. Looking at the diagram you can see that motion along the time frame "t2" which is true velocity would be greater than the 5,200 c "Proper Velocity" being observed.


***************** 1st Paragraph of the Presentation *********
When we observe Quasar jets from Earth, it is possible that the observed velocity of the jets appears to be greater than the speed of light. Because our current physical models allow for no mechanism that would allow such velocities to exist, we are left to devise some explanation that does mesh with our understanding of physical laws, while also explaining the observed velocities.
********************************************************************

To me this statement qualifies the process as something to "Ignore"

http://cosmos.colorado.edu/~maytag/superlum-math1.htm [Broken]
 
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  • #46
Funkee
After a while I've been compiling more ideas together for a different universal model, incorporating higher dimensions.

Since all matter as we know it has mass, then it must be moving. But direction and speed are technically impossible to determine without an external reference position. Once the KE reaches zero, the mass of an object will become zero. Then consider what we know of that has no mass. Few things there are we can observe that have no mass, but one comes to mind quickly. Light.

Photons have no mass. Suppose that the photons in the light beam have zero KE, they are not moving, at least not in our observable 4D. But that would make no sense. But then recall Kaluza-Klein, who said that light is a vibration in the 5th Dimension. Perhaps light may very well be vibrating in the 5th Dimension. It may be moving in the 5th dimension, collapsed as how it is, nevertheless, and yet motionless in our 4D. Since the light beam is not restricted to moving in only the 5th dimension, being parallel to our 4D, will mean we never notice it. But it does move through 3 (4) dimensions. But we observe it not to be moving within the 3. Then perhaps, we may use light, which is stationary as a reference point for absolute space and time.

If the light is stationary how is it that we see this beam of light moving at 300,000 km/sec. But consider the situation if we are the one's moving at that rate. The object emitting the light, which is matter, is moving with the rest of the universe at 300,000km/sec, and in result we have light travelling at that speed.

Due to entropy, the absolute paths to a stationary reference is chaotic. If we increase entropy, we are increasing KE, meaning we are increasing our mass, and travelling into the future. This is where the idea of travelling into the past comes up. To do so, we would have to reduce our movement, but to do so, we have to define the path of our bodies in relation to that fixed point to determine the absolute direction and speed. It is possible, but to do so would be far too difficult to imagine, consider the chaos of entropy as it is now.

And here again comes the point where you may not travel faster than light. Since the matter is moving away from the light at 300,000km/sec, and to observe the light beam moving away from us, we must in fact be moving away from it.

If you could imagine our space-time as a solid line, with the light beam intersecting it as such:

...........\
............\
.............\
_________\_____________
................\
.................\
...................\

The point of intersection is the reference point. We are moving in this --> direction, at 300,000km/sec. If we attempt to catch up to this light beam, our movement through space-time will decrease, time will pass us slower. Once we reach the light beam travelling away from us, we are at a stand still. But since our motion through space-time is essentially the entropy of the universe, our attempt to catch up to the light, by going faster simply adds additional KE to the chaotic movement of our bodies. So if we were to lower our KE in respect to absolute position, the light beam would move away from us at a slower rate. Once we reach zero KE, where we are at a stand still with space-time, we will catch up to the speed of light. To surpass light, we would need negative KE, which is a seperate discussion in itself.

I think that it is possible to attain speeds greater than 300,000km/sec, as those quasars that have been recorded. There is no limit in that direction as to your top speed, it's the minimum speed that sets the limit. In fact we will never catch up to the speed of light by going faster. If an observer was able to record the absolute speed of light as you moved faster through time, without being affected by time (which is technically impossible since velocity requires time), but suppose one could, that was not affected by time, travelling at such a speed to determine the velocity of the light beam in reference to absolute position, we would find that the light moves faster from us as we increase our speed. The fact that our travel through time and our speed is an inversely related, the product will always be a constant, which is in fact the speed of light. The distortion of time with a change in speed will keep the light beam moving from you at 300,000km/sec.

My idea. I'm only 15, forgive me if I may have contradicted some things or point me in the right direction regarding any mistakes. I've yet to take an official course in physics, but I've indulged myself pretty deep into this crazy theoretical stuff without knowing any of the math, so thanks for any insights and bothering to read all that.
 
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  • #47
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Originally posted by neutroncount
That's the stupidest thing I've ever heard. When I imagine myself someone else, that's just what it is. IMAGINING! My brain can visualize and create/recreate images, sounds and feelings because of our memories that are triggered from chemical reactions within our brain. Nothing at all is traveling faster than light. I hate to say it folks but our brain is just a peice of meat. A thinking peice of meat but no less a peice of meat. And I have a feeling you're not using yours enough.
But is "true thought" and thinking done through this "piece of meat" as you so amazingly put it? Or is there more to that?

To be honest, I have very special abilities ... however will only speak privatley with a person about them, not over the entire internet for millions of people to read.

I will leave it at that.
 
  • #48
drag
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Originally posted by Ploegman
To be honest, I have very special abilities ... however will only speak privatley with a person about them, not over the entire internet for millions of people to read.
Hey, there's that guy who'll pay you a million bucks
if you prove'em to him ! Go for it dude ! :wink:
 
  • #49
neutroncount
Originally posted by Ploegman
But is "true thought" and thinking done through this "piece of meat" as you so amazingly put it? Or is there more to that?

To be honest, I have very special abilities ... however will only speak privatley with a person about them, not over the entire internet for millions of people to read.

I will leave it at that.
Oh, so you're mentally ill? Yeah, that's something I wouldn't give out publicly either, to be honest. I will leave it at that.
 
  • #50
DR OF DEATH
the amount of times i have aired an opinion on this topic is unbelievable, ya know i just dont care anymore
 
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