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# speed of light

schumway
funny how some folks still believe we can not travel at the speed of light.

at one time it was thought we could not travel at the speed of sound and that has been blown away many times now.

It is interesting how celestrial objects travel around at high rates of speed without fuel...

I am sure there will be a time when we will travell faster than the speed of light. I do understand the theory re mass vs speed and etc

if something can travel at the speed of light... then it seems reasonable that you can travel faster than the speed of light. Also interesting that light is able to travel at it's speed and it does not have infinite mass. Why would something at the speed of light + 1 be infinit
The Conspirator
As an object moves faster its energy incises, at the speed of light the energy of an object would be infinite, so to move faster than the speed of light you would need an infinite amount of force.
Another problem is that as you increase in speed, time slows down and at the speed of light time would stop.

There are ideas of how though.
An Alcubierre drive, stretch the space behind a space ship and compares the space in front of it.
Change the speed of light.
Warm holes (though it would not tenthly be traveling faster than the speed of light.
Indi
 schumway wrote: at one time it was thought we could not travel at the speed of sound

This is a blend of myth and misunderstanding.

 schumway wrote: It is interesting how celestrial objects travel around at high rates of speed without fuel...

Interesting in what way?

 schumway wrote: I am sure there will be a time when we will travell faster than the speed of light. I do understand the theory re mass vs speed and etc if something can travel at the speed of light... then it seems reasonable that you can travel faster than the speed of light.

Why does this seem reasonable? Only a very few things can travel at the speed of light - not just any matter. For example:

 schumway wrote: Also interesting that light is able to travel at it's speed and it does not have infinite mass.

That is because photons do not have any rest mass. Anything that has a non-zero rest mass will have an infinite mass at c - but this does not include photons, because their rest mass is zero.

 schumway wrote: Why would something at the speed of light + 1 be infinit

You are asking the right questions, but this is something you would probably learn better from your teachers or an introductory book on physics, rather than some random forum on the internet.
Bikerman
 schumway wrote: funny how some folks still believe we can not travel at the speed of light. at one time it was thought we could not travel at the speed of sound and that has been blown away many times now. It is interesting how celestrial objects travel around at high rates of speed without fuel... I am sure there will be a time when we will travell faster than the speed of light. I do understand the theory re mass vs speed and etc

I don't think you do, or you wouldn't make statements like this.

Chris.
mayank_abhishek
Hey!!

Just one day in our class we were pulling the leg of our physics teacher.

He was explaining how Light travels faster than Sound. he proved it by explaining about thunder and lightening. How we see lightening before we hear thunder.

One of my friends very innocently cross questioned him, But sir when we switch on the television we hear the sound before we see pictures!

- Mayank
Psycho_X52
 schumway wrote: funny how some folks still believe we can not travel at the speed of light.

Einstein proved it.

Another physicist said that travelling at speed of light is possible, and you have to compress half of the universe (the half that is in front of you) and to enlarge the other half. The energy of 11 suns could be enough.
Sokken
but compressing the universe seems kind of difficult though
sonicj
I think the original posters point here is that in the past things were not thought possible by that times greatest minds, things that are now taken for granted. I for one think I am open-minded enough to leave room for the possibility of faster than light speed travel, although if ever it will be a long time from now. Not to mention...that if something is theory it is still not a scientific law.
mike1reynolds
 Indi wrote: Anything that has a non-zero rest mass will have an infinite mass at c - but this does not include photons, because their rest mass is zero.

An often stated overgeneralization. This constant velocity with zero acceleration.

Q: What accounts for the increase in mass?
A: The tilting of the observed hyperplane.

The hyperplane titles forward in time towards the direction of travel, and backwards in time away from the direction of travel. At c the hyperplane cuts directly through your own temporal axis. That slice can only be infinite if you have been traveling in that same direction at that same speed for an eternity, or you continued to do so for an eternity. If you are accelerating then your path will be curved four-dimensionally, and no hypeplane slice of such a 4D object can be infinite.

Indi wrote:
 schumway wrote: at one time it was thought we could not travel at the speed of sound

This is a blend of myth and misunderstanding.

But an interesting analogy none the less, because the faster you accelerate and the tighter your 4D curve, the smaller your mass as you hit c.

The first pilots to try to break the sound barrier all wrecked and many died because the generals thought the pilots should try to go slowly over the barrier. I think it was Chuck Yeager who finally said f**k this and took it on his own to hit the gas as hard as he could, and thus becoming the first person to cross the sound barrier.

Similarly, to get past the speed of light barrier you have to be accelerating fast enough. 100G’s would squash a human like a grape, so for all intents and purposes the speed of light is an impenetrable barrier for us.
kirancnair
Can the speed of light be slowed down?

I recently saw a Discovery Documentary about Camera. They were talking of cams that could capture light tarveling....

Well if we can actually control the speed of light..does this not mean that we have control over time..may be in a closed system...
Indi
 kirancnair wrote: Can the speed of light be slowed down? I recently saw a Discovery Documentary about Camera. They were talking of cams that could capture light tarveling.... Well if we can actually control the speed of light..does this not mean that we have control over time..may be in a closed system...

Yes and no. c is the speed of light in a vacuum. Light... appears... to travel at different velocities in different materials. You should know that light bends in water or glass due to the refractive index of those materials. For example, common glass has a refractive index of anywhere between about 1.5 to about 1.9, which means the speed of light is... apparently... 1.5-19 times slower in glass than in a vacuum.

But... is it really slower? Not really. There are two processes happening in a material that appear to slow down light.

The first is pretty simple - internal electric and magnetic fields within the molecule structures that make up the material (remember, atoms bond electromagnetically, so there are lots of these fields in a material) redirect the photons all over the place. So instead of travelling in a straight line, the photons zigzag through the structure. So the photons don't actually slow down, they still travel at c. They just have a longer path to travel.

The second is trickier. It involves photons being absorbed into the atoms of the material, knocking electrons up to a higher energy state, then being re-emitted when the electrons crash from their high. This process takes time, which effectively slows down the passage of the photons through the material. But they still travel at c.

Incidently... not only has light been "slowed" down to ridiculously slow speeds in the laboratory... it's been "stopped" dead.

There are many more complications. For example, it is possible to speed up light past c... sort of. Remember, a photon is a wave packet. Think of a sine wave shape like this: ∿∿∿ It is possible to make the front of that waveform travel faster than c. But the crucial shape information of that wave will still be c. So you could theoretically send a signal to planet 100 light years away so that the front of the signal will get there in an hour... but they won't know they have a signal until the rest of the packet information arrives... 100 years later. The front tip of the ∿ will arrive in an hour, but it will take 100 years to go from the front tip to the first peak.

As for whether slowing down light will give you control over time... i can't imagine what you mean. But remember that it is possible to "slow" light down thousands and thousands of times even today. i recommend this short story for a really neat example of what that would mean in terms of an interesting "practical" technology that involves manipulating time... sort of.
TerrorBite
 mike1reynolds wrote: Q: What accounts for the increase in mass? A: The tilting of the observed hyperplane. The hyperplane titles forward in time towards the direction of travel, and backwards in time away from the direction of travel. At c the hyperplane cuts directly through your own temporal axis. That slice can only be infinite if you have been traveling in that same direction at that same speed for an eternity, or you continued to do so for an eternity. If you are accelerating then your path will be curved four-dimensionally, and no hypeplane slice of such a 4D object can be infinite.

A hyperplane? That's a bit hard to conceptualize. Which axes would it be passing through? You're assuming background knowledge here. I happen to have some idea what a hyperplane is, but others might not. (then again, don't dumb it down too much.)

 Indi wrote: Incidently... not only has light been "slowed" down to ridiculously slow speeds in the laboratory... it's been "stopped" dead.

I've heard about this. They used some sort of laser-gas vapor arrangement at zero temperature or something.

 Indi wrote: ...then being re-emitted when the electrons crash from their high.

I now have this image in my head of these stoner electrons sitting around smoking pot.

Something I've always wondered... According to the theory of relativity, everything is relative. there is no 'absolute' against which we can measure things. So the question is... the speed of light (in a vacuum) relative to what?
the answer to that is, relative to the observer.
So if the observer is travelling at what (from, say, Earth) appears to be the speed of light, he will still see light going at the speed of light towards/away from him.

There's this problem:
"A ray of light goes from Observer A to Observer B when A and B are moving at different speeds." So if they're moving towards each other, won't the light ray emitted at speed c from A reach B at faster than c?
No, it'll arrive at what Observer B measures as c. But it will be blue-shifted. The Doppler effect solves that problem.

I believe that it's proven that the problem I stated above (the speed of light relative to what?) is solved by Doppler and also the time-compression/length-compression/mass-expansion effects of relativity. I'm really sketchy on the details though.
Bikerman
I think a key to this, and one which frequently gets overlooked, is the concept of intertial frames of reference. It took me a while to really 'get it' and without the concept firmly embedded in your mind it is easy to get confused about what is happening....I used to, all the time, now I only get confused half of the time which is a 100% improvement

Best wishes
Chris
Bikerman
 sonicj wrote: I think the original posters point here is that in the past things were not thought possible by that times greatest minds, things that are now taken for granted. I for one think I am open-minded enough to leave room for the possibility of faster than light speed travel, although if ever it will be a long time from now. Not to mention...that if something is theory it is still not a scientific law.

No. Science is all theory...theory does not mean 'not proven' it means something different in science. I don't want to bore everyone with my standard lecture on Induction and scientific method so I'll just give you a couple of links to follow....
Best wishes
Chris
http://dieoff.org/page126.htm
http://en.wikipedia.org/wiki/Theory
sonicj
Bikerman wrote:
 sonicj wrote: I think the original posters point here is that in the past things were not thought possible by that times greatest minds, things that are now taken for granted. I for one think I am open-minded enough to leave room for the possibility of faster than light speed travel, although if ever it will be a long time from now. Not to mention...that if something is theory it is still not a scientific law.

No. Science is all theory...theory does not mean 'not proven' it means something different in science. I don't want to bore everyone with my standard lecture on Induction and scientific method so I'll just give you a couple of links to follow....
Best wishes
Chris
http://dieoff.org/page126.htm
http://en.wikipedia.org/wiki/Theory

I think there is a distinction between theory and law. Quoting from websters:
 Quote: HYPOTHESIS, THEORY, LAW mean a formula derived by inference from scientific data that explains a principle operating in nature. HYPOTHESIS implies insufficient evidence to provide more than a tentative explanation . THEORY implies a greater range of evidence and greater likelihood of truth . LAW implies a statement of order and relation in nature that has been found to be invariable under the same conditions .
Bikerman
[quote="sonicj"]
I think there is a distinction between theory and law. Quoting from websters:
 Quote: HYPOTHESIS, THEORY, LAW mean a formula derived by inference from scientific data that explains a principle operating in nature. HYPOTHESIS implies insufficient evidence to provide more than a tentative explanation . THEORY implies a greater range of evidence and greater likelihood of truth . LAW implies a statement of order and relation in nature that has been found to be invariable under the same conditions .

Never believe non-science sources on these definitions, but in this case the definition is OK. Yes I know that law and theory are not interchangeble - I was obviously not clear, sorry. My point was that, from the perspective of being correct or not, there is no real difference.
The way I remember it is :
Law - normally simple statement of the way things behave
Theory - more dynamic and complete description of the behaviour and the causes
Hypothesis - conjecture or posit about how the system might be behaving and what the causes could be.

A law is an abstraction or a 'summary' which often includes several theories. Hence we have the law of gravity which is explained variously by Einsteinean Relativity theory or alternatively by Quantum Gravity.

I hope this is clear. The central point is that theory is not implying that it is just conjecture...it is a technical word meaning explanation....
sonicj
 Bikerman wrote: Never believe non-science sources on these definitions, but in this case the definition is OK.

I am not disagreeing with any of what you said, except this statement struck me as a little strange. Would that not be like saying I will use the bible only to prove the bible? (you may insert Koran or whatever you like in place of bible)
Bikerman
sonicj wrote:
 Bikerman wrote: Never believe non-science sources on these definitions, but in this case the definition is OK.

I am not disagreeing with any of what you said, except this statement struck me as a little strange. Would that not be like saying I will use the bible only to prove the bible? (you may insert Koran or whatever you like in place of bible)

No....not intended to be taken that way. The wider point is that words that are used in some science contextx have meaning different to the general meaning in normal language. If you check a dictionary for a definition of 'evolution' for example you get the following
 Quote: 1. A gradual process in which something changes into a different and usually more complex or better form. See Synonyms at development. 2. a. The process of developing. b. Gradual development.

 Quote: 4 a : the historical development of a biological group (as a race or species) : PHYLOGENY b : a theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations; also : the process described by this theory

 Quote: 1. (biology) the sequence of events involved in the evolutionary development of a species or taxonomic group of organisms - evolution, phylogeny, phylogenesis

Now these are the first 3 online dictionaries I chose and none give a satisfactory defintion 1 is downright misleading and 2&3 miss the mechanism out completely

That was the point. People frequently post things with definitions that they maintain proove the case. My point is that the definition itself needs to be scientific - therefore use a scientific dictionary - otherwise the debate starts from the wrong point....
I wasn't having a personal dig, just making the general point.

Regards
Chris
Bikerman
In theology one would expect to use specialist vocab and I would expect to have a theological definition. Same goes in science.
The abuse comes when the word is then reinterpreted and used differently from the previous agreed definition. This rarely happens in science....I won't comment on how often it happens in other fields...

Chris
Nyizsa
 Indi wrote: Yes and no. c is the speed of light in a vacuum. Light... appears... to travel at different velocities in different materials.

So the answer is yes, it is possible to travel (at least for particles) to travel faster than the speed of light - IN A CERTAIN MATERIAL!!!
Indi
Nyizsa wrote:
 Indi wrote: Yes and no. c is the speed of light in a vacuum. Light... appears... to travel at different velocities in different materials.

So the answer is yes, it is possible to travel (at least for particles) to travel faster than the speed of light - IN A CERTAIN MATERIAL!!!

No, the answer is still no. Even within that material, photons will still be zipping by you. It's just that they'll be bouncing around. You'll never move faster than a photon, but you may get where you're going before the photon does. That's effectively what happens in Čerenkov radiation - the photons are still moving at c, just not in a straight line. If you can plow something else through the material in a (relatively) straight line, such as electrons in the most common case of Čerenkov radiation, it will bypass the photons... but it will not be moving faster than the photons.

The other thing you may be misunderstanding is that it is possible to change the phase velocity of light. But the phase velocity is not the speed of light. The speed of light is the group velocity of the photon EM wave packet, and that is always c - in a material when it seems like you have slowed down the group velocity of photons, you haven't, you've just introduced absorbtion/re-emission and bouncing effects.
xyberz
Through recent research done, the speed of light has been surpassed by sound using sound pulses. Read the interesting article here:

http://www.shoutwire.com/viewstory/48895/Sound_Pulses_Exceed_Speed_of_Light
TerrorBite
 Bikerman wrote: I think a key to this, and one which frequently gets overlooked, is the concept of intertial frames of reference. It took me a while to really 'get it' and without the concept firmly embedded in your mind it is easy to get confused about what is happening....I used to, all the time, now I only get confused half of the time which is a 100% improvement

It's the inertial frames of reference that confuse me too. I believe the laws of relativity get a lot more complicated when the frames of reference are accelerating at a non-uniform rate.

 sonicj wrote: Would that not be like saying I will use the bible only to prove the bible?

"Proving the Bible" is an entirely different subject and deserves its own thread, if it doesn't already have one.
I can't be bothered to go and find one though.
Indi
 xyberz wrote: Through recent research done, the speed of light has been surpassed by sound using sound pulses. Read the interesting article here: http://www.shoutwire.com/viewstory/48895/Sound_Pulses_Exceed_Speed_of_Light

Not quite.
 http://www.shoutwire.com/viewstory/48895/Sound_Pulses_Exceed_Speed_of_Light wrote: None of the individual waves making up the sound pulses traveled faster than c. In other words, Einstein's theory of relativity was preserved. This means one could not, for instance, shout a message faster than light.

The article is contradictory and i believe the person writing it screwed up the physics. i believe he has confused group velocity and phase velocity in several places, and has used c as the speed of light in the material some places.

If the article actually means what i think it means - when i read it trying to filter out mistakes - then it is a pretty neat finding that is useful for signal routing and processing in fibre-optic systems. But it ain't FTL.

 sonicj wrote: Would that not be like saying I will use the bible only to prove the bible? (you may insert Koran or whatever you like in place of bible)

Just to comment: in science you don't actually try to prove anything... you try to disprove it. You start with a theory, then you pick out the parts of it that can be falsified - which means they can be tested and if the test fails, the theory is disproven - then you run your experiment.

So it would be rather like using the bible to disprove the bible (or quran, whatever) - or to use a science example, that would be like using a theory that predicts the existence of electrons to disprove that theory - which is a perfectly valid methodology.
sonicj
TerrorBite wrote:

 sonicj wrote: Would that not be like saying I will use the bible only to prove the bible?

"Proving the Bible" is an entirely different subject and deserves its own thread, if it doesn't already have one.
I can't be bothered to go and find one though.

I wonder if you even read what I wrote or just decided to take it out of context for your own reasons?
sonicj
 Bikerman wrote: That was the point. People frequently post things with definitions that they maintain proove the case. My point is that the definition itself needs to be scientific - therefore use a scientific dictionary - otherwise the debate starts from the wrong point.... I wasn't having a personal dig, just making the general point. Regards Chris

Point taken.
TerrorBite
 sonicj wrote: I wonder if you even read what I wrote or just decided to take it out of context for your own reasons?

I did take that out of context.

Yes, I can see that the shoutwire story does not claim sound exceeds the limits of relativity.

 The ShoutWire article wrote: ...transmitted sound pulses faster than light travels—at least according to one understanding of the speed of light. (emphasis added) Past research has proven it possible to transmit electrical and even light pulses with group velocities exceeding c. (emphasis added)

Agreed, the way he article is written is a bit confusing. The references to "speed of light", for example, are sketchy and give the impression that the sound is travelling faster than c and thus defying relativity, even if this is not what the article is saying.

Although on re-reading it, it seems maybe what it's saying is, the sound is going faster than c - just the information carried by the sound isn't.
Indi
 TerrorBite wrote: Agreed, the way he article is written is a bit confusing. The references to "speed of light", for example, are sketchy and give the impression that the sound is travelling faster than c and thus defying relativity, even if this is not what the article is saying. Although on re-reading it, it seems maybe what it's saying is, the sound is going faster than c - just the information carried by the sound isn't.

Yes, the article is a bit vague and confusing - i actually read it differently. i figured that when they said "speed of light", they didn't always mean c - sometimes they meant the speed of light in the medium (which will always be slower than c for any non-vacuum medium). It's quite possible for sound pulses to travel faster than the speed of light in a medium.

It's been a while since i did the math, but if i recall, it's pretty trivial to show with basic special relativity that all massless particles - in this case, photons - must travel at c in order to have any momentum. If these guys had shown that to be wrong, i think we'd be hearing a lot more about it.
Bikerman
 Indi wrote: It's been a while since i did the math, but if i recall, it's pretty trivial to show with basic special relativity that all massless particles - in this case, photons - must travel at c in order to have any momentum. If these guys had shown that to be wrong, i think we'd be hearing a lot more about it.

I can offer this rambling.....
http://camres.frih.net/resources/math/relmass.html

ahh....postscript.....I think I can do better with......
http://camres.frih.net/resources/math/relmass1.html

(I use a little plugin called livemath for this stuff - the viewer is free and integrates with ie, firefox, netscape et al.....you can download a copy from here if you wish and simply run to install. Alternatively you can visit the LiveMath site and check it out for yourself. I would download the free viewer and the free plugin if 't'were me...It basically allows complex math in a normal browser window and I love it (and no, I am not related or linked in any way to Livemath or any other software firm)....

Alternatively the last proof is here as a graphic image but it's horrible compared to the plugin

Fright Knight
 Quote: Please use quote tags when posting other peoples work. Tags added by Moderating Team The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning "swiftness". It is the speed of all electromagnetic radiation in a vacuum, not just visible light. In metric units, c is exactly 299,792,458 metres per second (1,079,252,848.8 km/h). Note that this speed is a definition, not a measurement. Since the fundamental SI unit of length, the metre, has been defined since October 21, 1983 in terms of the speed of light; one metre is the distance light travels in a vacuum in 1/299,792,458 of a second. Converted to imperial units, the speed of light is approximately 186,282.397 miles per second, or 670,616,629.384 miles per hour, or almost one foot per nanosecond. Through a transparent or translucent material medium, like glass or air, it may appear to have a different speed than in a vacuum; the ratio of c to the observed phase velocity (which may be both smaller or larger than c) is called the refractive index of the medium. Changes of gravity, however, warp the space the light has to travel through, making it appear to curve around massive objects. This gives rise to the phenomenon of gravitational lensing, in which large assemblies of matter can refract light from far away sources, so as to produce multiple images and similar optical distortions.
Jschoen43
i bet there is a form of energy out there that can make us travel the speed of light. we just havent found it yet. and even if there isnt i think it would still be could to keep trying anyways because it never hurts to learn more about the universe
NemoySpruce
 Jschoen43 wrote: i bet there is a form of energy out there that can make us travel the speed of light. we just havent found it yet. and even if there isnt i think it would still be could to keep trying anyways because it never hurts to learn more about the universe

I dont think so. c is the speed limit. no way we can travel faster than that. But I do believe that someday we will be able to manipulate space. By bending, folding, compressing and expanding space, we can appear to travel faster than light. I read somewhere that galaxies far away seem to be moving faster than the speed of light... how can this be? i thought c is relative? It has something to do with the Hubble constant, I dont really understand it that well, maybe someone can give a brief explanation how this is possible.
newolder
Nemoy Spruce> i thought c is relative?

A postulate of Special Relativity theory (Albert Einstein, 1905, Ann. Physik) is that c, the speed of light in vacuo, is the upper limit to the rate at which information is interchanged between space-time separated objects.

A useful explanatory tool is the light cone (Hermann Minkowski

1864-1909, Penrose 2007).

Have a great Google(tm) ! ed.
TerrorBite
Trying to get my head around a relative speed limit bends my brain. "Nothing can go faster than the speed of light..." "The speed of light relative to what?"

Yeah, light cones are a good tool to use.

 NemoySpruce wrote: ...c is the speed limit. no way we can travel faster than that. But I do believe that someday we will be able to manipulate space. By bending, folding, compressing and expanding space, we can appear to travel faster than light...

I agree with NemoySpruce here. Attempting to physically travel faster won't get us anywhere. Instead, we have to go... around, for lack of a better word. Manipulating spacetime would be the best way to do this. Possibly a craft could be "folded" into a "pocket" of space-time, like a miniature universe, that could be moved independently... or perhaps we might find a way of creating a stable wormhole.

I can't remember what the Hubble constant is.
nilsmo
We are all traveling at the speed of light, as explained before. And if someone (with mass) was to travel at the speed of light relative to us, they would have to exert an infinite amount of energy, which is impossible. So saying you can't go at the speed of light is saying "We're not smart enough to do that" it's saying that "Accepted equations tell us that it is physically impossible to go at the speed of light because that would require an infinite force."
NemoySpruce
Thanks. I got that. nothing with mass can travel at the speed of light, as the object's speed aproaches c, its mass increases, so more energy is needed to accelerate it. According to the theory,even if you have infinite energy, you will only attain infinite mass, but still not reach the speed of light.

But, why are there theories that say the universe is expanding faster than the speed of light?

 newolder wrote: Nemoy Spruce> i thought c is relative? A postulate of Special Relativity theory (Albert Einstein, 1905, Ann. Physik) is that c, the speed of light in vacuo, is the upper limit to the rate at which information is interchanged between space-time separated objects. A useful explanatory tool is the light cone (Hermann Minkowski 1864-1909, Penrose 2007). Have a great Google(tm) ! ed.
Bikerman
 NemoySpruce wrote: Thanks. I got that. nothing with mass can travel at the speed of light, as the object's speed aproaches c, its mass increases, so more energy is needed to accelerate it. According to the theory,even if you have infinite energy, you will only attain infinite mass, but still not reach the speed of light. But, why are there theories that say the universe is expanding faster than the speed of light?

Expansion is of space-time itself. Space-time expansion is not convered by the limitations of relativity because relativity describes objects in space-time, not space-time itself.
newolder
Bikerman wrote:
 NemoySpruce wrote: Thanks. I got that. nothing with mass can travel at the speed of light, as the object's speed aproaches c, its mass increases, so more energy is needed to accelerate it. According to the theory,even if you have infinite energy, you will only attain infinite mass, but still not reach the speed of light. But, why are there theories that say the universe is expanding faster than the speed of light?

Expansion is of space-time itself. Space-time expansion is not convered by the limitations of relativity because relativity describes objects in space-time, not space-time itself.

Hi Chris,

Nemoy may appreciate a link to your relativity theory pages at camres - they are clear, concise and correct, from what i recall.

Cheers again, ed.

P.S. How would one make observations of things that travel faster than c?
Tumbleweed
If "c" is the speed of light and the speed of light is as fast as anything could possibly go, why did'nt they call it "z" ?
Bikerman
 newolder wrote: Nemoy may appreciate a link to your relativity theory pages at camres - they are clear, concise and correct, from what i recall.
Thanks Ed....I'll put up what I've got
Time dilation
General cosmology
Very Early Cosmology
 Quote: Cheers again, ed. P.S. How would one make observations of things that travel faster than c?

It would be outside the 'light cone' and therefore outside the area of interaction wouldn't it ?
newolder
Bikerman wrote:
 newolder wrote: Nemoy may appreciate a link to your relativity theory pages at camres - they are clear, concise and correct, from what i recall.
Thanks Ed....I'll put up what I've got
Time dilation
General cosmology
Very Early Cosmology
 Quote: Cheers again, ed. P.S. How would one make observations of things that travel faster than c?

It would be outside the 'light cone' and therefore outside the area of interaction wouldn't it ?

Re- Tachyons*.

I don’t have your line-drawing skills but I think I can put it into words.

For a tachyon to exist in reality it must interact with the observable universe somehow.

On a timeline going up the page, draw a light cone at the origin of an orthogonal axis-set (x across and y into the page). We are free to move the origin anywhere on (or even off!) the page so, let’s put it on a tachyon’s track.

Since the tachyon’s speed over the x-y plane is always >c, the angle between the tachyon’s track and the x-y plane is always less than π/4 radians.

Consequently, the tachyon only interacts with my brain (no pun intended) at the origin. Experimentally, one would see and not see the tachyon simultaneously. Now, that is definitely stranger than I thought I could think. ed.

* Pub-quiz-type answer to, "What is a tachyon?" :: "A Mexican bread-snack."
Bikerman
Something like this ?
newolder
 Bikerman wrote: Something like this ?

More evidence that physics is simple to demonstrate.

It seems i'm learning to write it down too.

ed.

I'll wager your skills are able to extend that model a little further...

The (blue) oval at cone-top-surface, as drawn, can be considered the world-sheet of the photon. Any particle with the property mass=true can, by the rubber-sheet analogy, be shown to have a world-sheet that funnels towards the origin as the amount of mass -> infinity. The funnel also gets red-shifted (Doppler effect) as the mass increases and, hence, the distance from the origin (A) decreases.

It is the 'crowding together'-ness of these world-sheets that determines reality: i.e. does a minimum separation, a.k.a. the Planck length, mass/energy, time/frequency, temperature/entropy exist in observed reality or not?

ed.

mathiaus: post merge
mom-9
HI ,
i know just that :
E = m * C²
newolder
 mom-9 wrote: HI , i know just that : E = m * C²

Hi mom-9,

It reads like you are familiar with one branch of 20th century reason, are you aware that quantum theory, another branch, was discovered to improve the model of reality around the same time too?

On a related topic*, FunDa writes: “Mass is energy. Just lots of energy.
E=mc^2”. The remainder of the topic may be of interest… ed.

* http://www.frihost.com/forums/vp-584625.html#584625
newolder
 mom-9 wrote: HI , i know just that : E = m * C²

Hi mom-9,

It reads like you are familiar with one branch of 20th century reason, are you aware that quantum theory, another branch, was discovered to improve the model of reality around the same time too?

On a related topic*, FunDa writes: “Mass is energy. Just lots of energy.
E=mc^2”. The remainder of the topic may be of interest… ed.

* http://www.frihost.com/forums/vp-584625.html#584625
Bikerman
 newolder wrote: I'll wager your skills are able to extend that model a little further....

I tried....Tricky...I think this is on the right lines....
NemoySpruce
Bikerman wrote:
 newolder wrote: Nemoy may appreciate a link to your relativity theory pages at camres - they are clear, concise and correct, from what i recall.
Thanks Ed....I'll put up what I've got
Time dilation
General cosmology
Very Early Cosmology
 Quote: Cheers again, ed. P.S. How would one make observations of things that travel faster than c?

It would be outside the 'light cone' and therefore outside the area of interaction wouldn't it ?

@bikerman and newolder

Thanks for the links. my brain gave out a few paragraphs into the last link (Early Cosmology-A paper for the interested layman) I will keep at it, with a bit of help from wikipedia. I will try to understand it though my math isnt that advanced. I think its awesome that you are trying to explain physics to lay folk like us.

I have a question. In your Early cosmology page , why is gravity explained as a fundamental force? I thought gravity is a property of space/time. It is not a force that acts on an object, it is just an effect of space being warped by an object's mass.

 Bikerman wrote: Expansion is of space-time itself. Space-time expansion is not convered by the limitations of relativity because relativity describes objects in space-time, not space-time itself.

I guess you are right, space-time is exempted, but what about the galaxies in it?. If I understand the inflation theory correctly, it is saying that galaxies that are far from us are moving away faster than the speed of light. so the 'galaxy' is 'moving' away from us 'faster' than c!! because space is expanding.

 newolder wrote: How would one make observations of things that travel faster than c?

What do you mean? why would that be a problem?

I guess if an object was able to travel from point A to B faster than c. It would really be weird. I imagine if a FTL craft travels from the sun to earth, you could be still watching it break sun orbit while it was already orbiting the earth.
newolder
Hi both,

NemoySpruce, thanks for the encouraging words.

Issues around ‘what is gravity’ were resolved in 1998 with the publication of Ph.D. theses by Paul J. Steinhardt and Neil Turok. Essentially, General Relativity theory in four dimensions, GR4, (the best theory of gravity to that date) breaks down/blows up as the speeds of massive objects get (very) close to c. It turns out that mechanics in the space-time of GR4 (Minkowski) can be solved easiest using Kaluza/Klein analysis where one, extra and large space dimension is employed. (A mathematical trick that didn’t purport to represent reality when first discovered.)

In quantum mechanics, forces are seen as the exchange of bosons: e.g. the photon (the carrier of the electromagnetic force) is an uncharged (neutral), spin 1 boson: the exchange of momentum in quantum systems has six degrees of freedom (up/down, left/right, fore/aft). Quantum gravity theorems must include something of this quantisation too.

Since 4 + 1 + 6 = 11, 11-dimensional supergravity theory emerged from the, earlier and stringy, mist and some current researches (LHC@CERN, Tevatron@USA and many and various telescopes on Earth and in the space beyond) are focussed towards finding/making experiments to falsify the predictions 11-D SUGRA theory makes.

If you don’t see the problem in a single object being at separate locations simultaneously, I don’t think I can help any further except to say, that road leads only to great fantasy.

Nice try, Chris! Words fail me at the moment. Let me get back to you later?

ed.
NemoySpruce
 newolder wrote: Issues around ‘what is gravity’ were resolved in 1998 with the publication of Ph.D. theses by Paul J. Steinhardt and Neil Turok.

wikipedia doesnt have anything Steinhardt and Turok did in 1998. It does say something about a Cyclic Model for the universe but they did it in 2001.
Do you have any links to any text that has 'resolved' gravity? I want my flying car now.

 newolder wrote: Essentially, General Relativity theory in four dimensions, GR4, (the best theory of gravity to that date) breaks down/blows up as the speeds of massive objects get (very) close to c.

what exactly does 'breaks down/blows' up mean?

 newolder wrote: It turns out that mechanics in the space-time of GR4 (Minkowski) can be solved easiest using Kaluza/Klein analysis where one, extra and large space dimension is employed. (A mathematical trick that didn’t purport to represent reality when first discovered.) In quantum mechanics, forces are seen as the exchange of bosons: e.g. the photon (the carrier of the electromagnetic force) is an uncharged (neutral), spin 1 boson: the exchange of momentum in quantum systems has six degrees of freedom (up/down, left/right, fore/aft). Quantum gravity theorems must include something of this quantisation too.

Quantum gravity theorems must include quantisation of force.... therefore gravity is a force? its not. its a property of space-time.

 newolder wrote: Since 4 + 1 + 6 = 11, 11-dimensional supergravity theory emerged from the, earlier and stringy, mist and some current researches (LHC@CERN, Tevatron@USA and many and various telescopes on Earth and in the space beyond) are focussed towards finding/making experiments to falsify the predictions 11-D SUGRA theory makes.

I checked wikipedia. They say this SUGRA thing failed.

 Quote: Some of these difficulties could be avoided by moving to a 10-dimensional theory involving superstrings. However, by moving to 10 dimensions one loses the sense of uniqueness of the 11-dimensional theory.

 newolder wrote: If you don’t see the problem in a single object being at separate locations simultaneously, I don’t think I can help any further except to say, that road leads only to great fantasy.

isnt this what we do when we treat a particle as a wave?
newolder
Although wikipeadia is a fine resource, it's not always up-to-date with regard to things physical. You could always try the authors' home pages.

Neil Turok's is here :: http://www.damtp.cam.ac.uk/user/ngt1000/

and

Paul J. Steinhardt's here :: http://www.physics.princeton.edu/~steinh/

Their recent publications lists show that 11-D SUGRA theory is alive, kicking and well.

I don't think you'll find any (controlled) flying cars other than those powered by quintessence, rockets or perhaps helicopter technology.

The singularities of GR4, e.g. inside a gravitational black hole and near T(Observable Universe) = 0, are the same as the theory blowing up/breaking down.

Gravity is, as you say, responsible for the curvature of space-time but any quantised theory will have its associated messenger particle included too. The Higgs particle is a likely candidate that the LHC@CERN will give more information anent after November of this year (all being well).

NemoySpruce>isnt this what we do when we treat a particle as a wave?

No.

Cheers again, ed.
Bikerman
 NemoySpruce wrote: Thanks for the links. my brain gave out a few paragraphs into the last link (Early Cosmology-A paper for the interested layman) I will keep at it, with a bit of help from wikipedia. I will try to understand it though my math isnt that advanced. I think its awesome that you are trying to explain physics to lay folk like us.
You are welcome.
 Quote: I have a question. In your Early cosmology page , why is gravity explained as a fundamental force? I thought gravity is a property of space/time. It is not a force that acts on an object, it is just an effect of space being warped by an object's mass.

Yes, interesting point. Newolder explains better than I could so I'll consider that covered unless you want to pursue it further...
 Quote: I guess you are right, space-time is exempted, but what about the galaxies in it?. If I understand the inflation theory correctly, it is saying that galaxies that are far from us are moving away faster than the speed of light. so the 'galaxy' is 'moving' away from us 'faster' than c!! because space is expanding.

This is expansion not inflation...inflation describes a different process. Galaxies themselves do not 'expand' because expansion only occurs where there is insufficient gravity to cancel the expansive force - deep intergalactic space. Distant galaxies are, in a real sense, not moving away from us at all, rather the space in-between is expanding.
Bikerman
Hi Newolder....here's an attempt at animating the 'funnel-space'
newolder

When Ardman and Pixar get to see this, who knows where that combined imagination may lead? Good stuff! Cheers again, ed.

Thalipolibrothers
no not really
Thalipolibrothers
not really
boywert
Anyway, there is somthing that Einstein said and I think it will be true forever

Gavitational attraction cannot be responsible people who are falling in love.

hahaha
Indi
 boywert wrote: Anyway, there is somthing that Einstein said and I think it will be true forever Gavitational attraction cannot be responsible people who are falling in love. hahaha

Oh heavens no. It couldn't be the gravitational force.

It is the electromagnetic.
Bikerman
Actually General Relativity can be applied to love but it's illegal in most countries.
TerrorBite
I thought the combination of the theories of romance and quantum physics was the next big thing.

Seriously though, I've been away for a week and the conversation has already reached the point where I need to do some serious reading to keep up. My brain hurts.

_________________
So many Frihost points to make up, and yet so little to say...
newolder
 Bikerman wrote: Something like this ?

MWC 922 has been imaged* and a pi/4 anticlockwise rotation of a light cone-like structure made of forsterite, apparently, is revealed...

Why anyone calls it the red square nebula defeats me. ed.

* http://www.msnbc.msn.com/id/18082430/

P.S.

The image is made from data collected at two telescopes (Keck, Hawaii and Mt Palomar, mainland). There must be some phase information to build a proper, animated hologram, surely?

From source:

Tuthill and Lloyd spotted the Red Square using the 200-inch Hale Telescope at Caltech’s Palomar Observatory and the Keck-2 Telescope in Hawaii."

P.P.S.

Beautiful.

For a Hubble-view of HD 44179 : The Red Rectangle nebula.

I wonder if Kurt Vonnegut Jr saw anything like this? ed.
Teezgaff
Hi all (been away for a while).....

The speed of light.... I'm just looking for the article which in effect a team of physicists slowed light down to around 40 miles per second.. Also another where scientists encouraged light pulses to travel in a bunch. Something about a group velocity making the whole greater than the sum..

Anyone else heard of this??
Bikerman
 Teezgaff wrote: Hi all (been away for a while)..... The speed of light.... I'm just looking for the article which in effect a team of physicists slowed light down to around 40 miles per second.. Also another where scientists encouraged light pulses to travel in a bunch. Something about a group velocity making the whole greater than the sum.. Anyone else heard of this??

Yes indeed. The techniques I have heard of involve using a Bose-Einstein Condensate (BEC) of sodium (sodium cooled down to a few billionths of a degree above absolute zero).*
As far as group velocity is concerned:

vg is the group velocity ω is the wave's angular frequency k is the wave number

In most cases the group velocity is equal to the signal velocity (the velocity at which information is conveyed). This is not always the case, however; particularly when the signal is travelling through an absorbent medium. http://www.mathpages.com/home/kmath210/kmath210.htm

* http://www.europhysicsnews.com/full/26/article1/article1.html
* http://www.dailycal.org/sharticle.php?id=16946
Teezgaff
Bikerman wrote:
 Teezgaff wrote: Hi all (been away for a while)..... The speed of light.... I'm just looking for the article which in effect a team of physicists slowed light down to around 40 miles per second.. Also another where scientists encouraged light pulses to travel in a bunch. Something about a group velocity making the whole greater than the sum.. Anyone else heard of this??

Yes indeed. The techniques I have heard of involve using a Bose-Einstein Condensate (BEC) of sodium (sodium cooled down to a few billionths of a degree above absolute zero).*
As far as group velocity is concerned:

vg is the group velocity ω is the wave's angular frequency k is the wave number

In most cases the group velocity is equal to the signal velocity (the velocity at which information is conveyed). This is not always the case, however; particularly when the signal is travelling through an absorbent medium. http://www.mathpages.com/home/kmath210/kmath210.htm

* http://www.europhysicsnews.com/full/26/article1/article1.html
* http://www.dailycal.org/sharticle.php?id=16946

The cross reference that I remembered is quoted as follows:-

 Quote: Astonishing Einstein The world of physics is a quirky, fickle field where very large ideas about the nature of time and space and our human place in it seem to be under constant reconsideration. But there was always one thing the harried physicist could depend on: the speed of light. Albert Einstein's theory of relativity declares that when light travels through a vacuum, its speed never changes. At 186,000 miles' per second, to be precise, light holds the top speed record for anything in the universe. Recent experiments, though, suggest that not even the speed of light is sacred. In 1999 an American team of physicists slowed light to a comparatively tortoise-paced speed of thirty-eight miles per second. -Then, in the July 10, 2000, issue of Nature, other scientists reported having urged their light speed forward, speeding up the light pulse to exceed the cosmic limit. They accomplished this feat by encouraging pulses to travel in a bunch. This gave them a "group" velocity, making the whole greater than the sum of its parts. Together, the bunched pulses could go over the speed limit set by Einstein, even if none of the individual waves did so. The major news implied in this finding is that when the speed of light is exceeded even by a factor of 1/300, the light appears to travel backward in time. We'll be looking at this idea later. But although Einstein's pickled brain may be twitching, the foundations of physics are not quaking: The experiments don't violate any of the established physical laws of nature, but they do show that it is possible to manipulate light—and possibly time—in ways that astonish scientists across the board.

Hope that gives a better insight into the stuff I get around to reading... LOL..
frih
speed of light is decreasing . i dont know the reason but you can search it on google.
Bikerman
 frih wrote: speed of light is decreasing . i dont know the reason but you can search it on google.

No, it isn't. This is an argument frequently put forward by YEC (Young Earth Creationists) in order to try and explain why the universe is as young as they say. There is no reputable scientific support for the idea and certainly no experimental or observational data to support the notion.
If you examine all the recorded speeds for light over history you get :

YECs modified this by excluding 'values which did not come under the proposed hypothesis'. What this actually means is that they disgarded many of the most recent and most accurate measurements which has the effect of skewing the best fit line on the graph slightly thus:

It's bad (dishonest) science and nobody in the scientific community takes it seriously.
speed of light is decreasing.

how did i find this?

Full-time researcher in cosmology. Before graduating I learned that the speed of light is slowing down and came up with the GM=tc^3 equation, which most physicists still can't explain. More recent work seeks Black Holes in some very unexpected places. I enjoy exploring a strange world and unusual forms of life.

I thought she was joking until I saw this - http://www-conf.slac.stanford.edu/einstein/talks/aspauthor2004_3.pdf

The above link is an abstract and is in PDF..and was given as a talk to Stanford Univ. just to say that I'm not joking.
Bikerman
 pradeep wrote: speed of light is decreasing.
Nah..
 Quote: how did i find this? one lady/woman had this written on her about me in her blog - Full-time researcher in cosmology. Before graduating I learned that the speed of light is slowing down and came up with the GM=tc^3 equation, which most physicists still can't explain. More recent work seeks Black Holes in some very unexpected places. I enjoy exploring a strange world and unusual forms of life.
Hmmm...interesting.
It is certainly not crank physics - Riofrio is a respected physicist - but it's not something I've come across before. I've cleaned up a paper by Riofrio on the matter (it was graphics and nasty - I've OCRd it and tidied it up a bit).
Here is the article in PDF
Here it is in HTML

There is also an article where she explains the theory is more accessible language...
EanofAthenasPrime
 schumway wrote: funny how some folks still believe we can not travel at the speed of light. at one time it was thought we could not travel at the speed of sound and that has been blown away many times now. It is interesting how celestrial objects travel around at high rates of speed without fuel... I am sure there will be a time when we will travell faster than the speed of light. I do understand the theory re mass vs speed and etc if something can travel at the speed of light... then it seems reasonable that you can travel faster than the speed of light. Also interesting that light is able to travel at it's speed and it does not have infinite mass. Why would something at the speed of light + 1 be infinit

I believe it perhaps would be best if you put a little wikepedia research in before attacking beliefs scientists have had for almost a century.

I am not saying it is bad to challenge mainstream beliefs; however you are not confident in what you are saying. QUOTE: "Why would something at the speed of light + 1 be infinit"
This sentence implies you have no basic knowledge of Einstein's physics.

Let me explain why scientists believe mass cannot travel at or beyond lightspeed.

c=speed of light
t=travelers time
t0=observers time

t=t0/sqrt(1-sqr(v)/sqr(c))

It has been proven with accurate atomic clocks that this equation works.
So, if v is equal to greater than c, division errors occur, leaving the assumption that matter cannot travel faster than c. To back this up, scientists have not been able to send matter through particle accelerators faster than c as well.
why not?
EanofAthenasPrime

because they aren't able to. Why not build a particle accelerator of your own?
@EanofAthenasPrime -

Sorry, the question was directed at Bikerman.
ssthanapati
As the object gets accelarated it has more and more energy. Wen the object is near the speed of light its mass would start reducing and convert into energy. When it reaches the speed of light the mass would simply vanish as all of it would have been converted to energy. Hence theoretically and mathematically an object can never reach the speed of light nor cross it.

But crossing the speed of sound was never impossible theoretically, it was impossible cause proper technology wasen't available at that time
Bikerman

I presume the question is why can we not travel at the speed of light (c) ?

The reason is only clear when you study Relativity. Many people give half-explained reasons, such as 'mass becomes infinite at c' or 'time stops at c' which are true as far as they go but are not reasons for the limit in themselves, rather they are the results/effects observed when we try to break c. In order to understand this part of the picture of reality, we need to look at the first part of Relativity theory - the Special Theory of Relativity (SR) which agrees that, just as Newton thought, speed is relative. It doesn't mean anything to say 'I am travelling fast' unless you have a reference point to measure your speed against. That is what we mean by 'relative' and it has long been understood that speed works in that way.

SR, however, says that, as well as speed, time itself is relative - ie not only is speed dependant on what reference point you measure it against, so is time. In the same way that your speed changes as you measure it with reference to different points of view (or 'frames of reference'), your time also changes depending on what reference frame you compare it to. This is NOT how we are used to seeing reality.

The special theory of relativity basically says that the rules of physics work for everyone the same, as long as they are not accelerating (which is a special case dealt with in the General Theory of Relativity). So a man travelling on a train at high speed and a man 'stationary' on the platform can both do the same sort of experiments and get the same sort of results because the rules (laws) of physics operate the same for both.

That's the easy bit. The hard bit is that SR also says that the speed of light is constant for all observers, no matter how fast they are moving.

So if the man on the platform shines a torch at the back of the train as the other man passes at high speed, the light photons will move away from the stationary man at a speed of around 30000000000 metres per second. The thing is, though, that the man on the speeding train WILL ALSO see the photons travelling at the same 30000000000 metres per second, even though he is moving away from the torch at (say) 50 metres per second himself. He will NOT see the light travelling at 29999999950 metres per second.

This is strange to us, because we are used to the fact that when we move we see other things moving at a speed which depends on our own speed. If I threw a brick at the train as it passed at (say) 30 metres per second, then, relative to the train, the brick would be travelling at -20 metres per second (ie it would be moving away from the train at 20 m/s). This is life as we are used to it and it works fine for slow moving things here on earth. Most people are comfortable with this picture of reality and believe that this is how things work everywhere. Unfortunately this is NOT how the world works - it only works this way at slow speeds, in situations of relatively low gravity and mass, but because that is exactly the world that we live in, it is tempting to assume that what applies in our little part of the universe should apply everywhere else.

SR, however, tells us that this is not the case with that simple seeming single rule - that light travels at the same speed for all observers (who are not accelerating), regardless of how fast they are moving. When you think through the implications of that simple sounding rule then you will begin to see that things are much different than you thought. You should also be able to begin to see why the speed of light is a maximum value.
newolder
 pradeep wrote: speed of light is decreasing. how did i find this? one lady/woman had this written on her about me in her blog - Full-time researcher in cosmology. Before graduating I learned that the speed of light is slowing down and came up with the GM=tc^3 equation, which most physicists still can't explain. More recent work seeks Black Holes in some very unexpected places. I enjoy exploring a strange world and unusual forms of life. I thought she was joking until I saw this - http://www-conf.slac.stanford.edu/einstein/talks/aspauthor2004_3.pdf The above link is an abstract and is in PDF..and was given as a talk to Stanford Univ. just to say that I'm not joking.

Is your name L. Riofrio, in reality? Otherwise, any simple dimensional analysis shows the same. What do you mean when you write that physicists can't explain this equation? It's trivial. ed.
Bikerman
What I don't understand is the derivation of the expression.
Riofrio says that GM = tc3 is a prediction of theory but doesn't elaborate. What theory, I wonder, produces this simple relationship?
I thought initial inflation was caused by a 'cosmological Higgs field' and that doesn't look like an expression derived from fields - it looks like a relativity expression. The only relativity equation I know which could be relevant to this situation is Einstein's
where

but I can't see how to get from that to

Any ideas Ed?
newolder
Furthermore, why does poster Pradeep think that the equation shows that c is slowing down? Utterly, sunday-baffled. So it goes... ed.
Bikerman
Hang on...I've just re-read the author's site......I think I may have the wrong physicist...I thought I knew Riofrio but judging from the site intro it sounds like a different person:
 Riofrio wrote: Full-time researcher in cosmology. Before graduating I learned that the speed of light is slowing down and came up with the GM=tc^3 equation, which most physicists still can't explain. More recent work seeks Black Holes in some very unexpected places. I enjoy exploring a strange world and unusual forms of life.

Sounds nothing like the physicist I thought I meant.....
newolder
Riofrio(?)>"Before graduating I learned that the speed of light is slowing down and came up with the GM=tc^3 equation, ..."

The last clause (...) is irrelevant; the first clause demonstrates bad teaching and the third (middle) is true but nothing to do with either of the others. It's like: I live here and you are a banana, they don't fish.

Carp (anag.) ed.
@newolder -
I wish I was but I am not L. Riofrio. That's a woman.

@bikerman -
I think you'll have to read the whole paper to get at that. Maybe, you should try arxiv.org? The above was only an abstract. I think she's written down the steps in her equation somewhere on her blog.

Even I am trying to understand what she's trying to say.
newolder
 pradeep wrote: @newolder - I wish I was but I am not L. Riofrio. That's a woman. @bikerman - I think you'll have to read the whole paper to get at that. Maybe, you should try arxiv.org? The above was only an abstract. I think she's written down the steps in her equation somewhere on her blog. Even I am trying to understand what she's trying to say.

newolder
 Bikerman wrote: What I don't understand is the derivation of the expression. Riofrio says that GM = tc3 is a prediction of theory but doesn't elaborate. What theory, I wonder, produces this simple relationship? I thought initial inflation was caused by a 'cosmological Higgs field' and that doesn't look like an expression derived from fields - it looks like a relativity expression. The only relativity equation I know which could be relevant to this situation is Einstein's where but I can't see how to get from that to Any ideas Ed?

Simple dimensional analysis shows the equality of the quantities [G x mass] and [time x (the speed of light in a vacuum)cubed)

viz:

[] means, 'units of'.

[G x mass] are [G x kilogramme, kg]

Since, [G] are [metres cubed per kilogramme per second squared] = [m^3 kg^-1 s^-2], we have [G x kg] = [m^3 s^-2]

and [tc^3] = [seconds x metres cubed per second cubed] = [m^3 s^-2] as required. ed.
ptolomeo
As a good physicist would say, the perfect theory does not exist. All we can do is to make them describe nature more and more precisely (the term precise is a little ambiguous here), so we approximate more and more to the truth but never reach it. In this way, Galilean relativity is a very good approximation to nature for relative velocities much smaller than the speed of light, but as we approach that speed, there is a more correct theory that describes nature, that is Einstein relativity. We would be very obtuse if we think that Einstein relativity is the last word, it would go against the general beleive that all theories are approximations. What we should think is that under "some assumptions" the speed of light is constant and is the maximum relative velocity between two bodies. I dont know what this assumption would be. In the nineteen century it was assumed that Galilean relativity would stand at very high velocities. It turn out to be a false assumption in the end. Something similar can happen (and must happen) with Einstein relativity, although we still dont know what is the scenario in which Einsteint relativity does not hold. Surely we will have to wait for some other genius to realise where Einsteint relativity brakes down.
newolder
 ptolomeo wrote: As a good physicist would say, the perfect theory does not exist. All we can do is to make them describe nature more and more precisely (the term precise is a little ambiguous here), so we approximate more and more to the truth but never reach it. In this way, Galilean relativity is a very good approximation to nature for relative velocities much smaller than the speed of light, but as we approach that speed, there is a more correct theory that describes nature, that is Einstein relativity. We would be very obtuse if we think that Einstein relativity is the last word, it would go against the general beleive that all theories are approximations. What we should think is that under "some assumptions" the speed of light is constant and is the maximum relative velocity between two bodies. I dont know what this assumption would be. In the nineteen century it was assumed that Galilean relativity would stand at very high velocities. It turn out to be a false assumption in the end. Something similar can happen (and must happen) with Einstein relativity, although we still dont know what is the scenario in which Einsteint relativity does not hold. Surely we will have to wait for some other genius to realise where Einsteint relativity brakes down.

The 21st century sees greater advances than 20th century physics knew it couldn't cope to understand and some are still working towards helping this understanding become more widespread*: Bikerman is doing a great deal to help too.

* http://www.universetoday.com/2006/04/11/podcast-dark-energy-stars/
Bikerman
 newolder wrote: Bikerman is doing a great deal to help too.

(blush mode) Kind words indeed. (/blush mode)
In all seriousness I think it is important that science should be made accessible to the general public. I am not a scientist but, as an 'educator', I think it is incumbent on me to do my part. In this endeavour I am reliant on those, like Ed, who have more knowledge than I, to correct and elaborate on my postings - and I am grateful for contributions from such posters.
dwinton
 schumway wrote: funny how some folks still believe we can not travel at the speed of light. at one time it was thought we could not travel at the speed of sound and that has been blown away many times now. It is interesting how celestrial objects travel around at high rates of speed without fuel... I am sure there will be a time when we will travell faster than the speed of light. I do understand the theory re mass vs speed and etc if something can travel at the speed of light... then it seems reasonable that you can travel faster than the speed of light. Also interesting that light is able to travel at it's speed and it does not have infinite mass. Why would something at the speed of light + 1 be infinite

Wow! You clearly do not understand relativity at all. Mass changes according to the equation mass = mass(orgininal)/sqrt 1 -v2/c2). Light has no mass ergo the equation yields 0/0 but if you are clever and use tensor calculus it just ends up remaining 0. Virtual particles can go at the speed of light because they have no mass. It has been observed that objects that are accelerated and should be going the speed of light are in fact going much slower. Since it is through an increase in kinetic energy that the objects are accelerated, the only thing that could account for this is an increase in mass.

The thing is, objects can traverse distances in times that seem to make them go faster than light if we look at two different frams of reference. for example: a rocket is moving at 90% the speed of light away from the earth towards something 90 light-years away. To the person on earth, it takes the rocket 100 years to make it to the something. However, to the rocket, it feels like it has been 100sqrt(0.19) years. The reason the rocket doesnt believe it has gone faster than light is the distance also contracts by the same amount.