# Could we, can we, will we ever travel at the speed of light or faster than the speed of light?

## News Feb 2012

From Slashdot: "It would appear that the hotly debated faster-than-light neutrino observation at CERN is the result of a fault in the connection between a GPS unit and a computer. This connection was used to correct for time delays in the neutrino flight, and after fixing the correction the researchers have found that the time discrepancy appears to have vanished."

NEWS July 2011

A group of physicists at the Hong Kong University of Science and Technology (HKUST) led by Prof Shengwang Du reported the direct observation of optical precursor of a single photon and proved that single photons cannot travel faster than the speed of light in vacuum. HKUST's study reaffirms Einstein's theory that nothing travels faster than light and closes a decade-long debate about the speed of a single photon. See link.

#### Original work. Sept 2009. Revision 1.0

Revision 1.1 : added an alternate explanation for constant speed of light.

## An age-old question

For many years, we have wondered if there is a way to travel faster than the speed of light. Alas, not only can we not do that, we cannot even send a signal faster than light. To do so would allow us to see what will happen before it happens. At a non-quantum scale, cause always precedes effect.

## Faster than light signalling is nearly as impossible as the paperless office.

Rest mass:

The traditional way to define rest-mass is as stated by Galileo and Newton. They defined mass as that property of a body that governs its acceleration when acted on by a force.

Particles like a proton or electron have a non-zero rest-mass. For example, the rest-mass of all electrons is 9.10938188 x 10-31 Kilograms, and all electrons have exactly the same mass. Rest mass is an intrinsic property of the object.

A photon however, has no rest mass and yet it is the carrier for the electromagnetic force. How then, can something with no mass take part in a physical interaction like a solar-cell? If a photon has no mass, how is it able to knock electrons about and make an electric current? You will read, no doubt that light from a distant planet is bent by a gravitational field. How can it be influenced by a gravitational field if it has no mass?

## Photons are influenced by a gravitational field.

An animated picture showing how light is bent by the gravitational field of a black hole. Credit: http://commons.wikimedia.org/wiki/File:BlackHole_Lensing.gif where permission and conditions are found.

## Relativistic Mass

I am going to start this with the traditional explanation of relativistic mass, but try to read this as just one of a possible number of explanations - not that it is wrong, but just with the mind that although this is a common explanation, it is not the only way to look at things. At the end of this section I will present another approach on how to understand the constant speed of light.

Surprisingly, confusion about mass is seldom explained clearly in elementary texts, and taken for granted in more advanced treatments.

Einstein's famous E=Mc2 equation shows that mass and energy are related. We know that a photon has energy, and we know that it moves at 299 792 458 meters every second. This has the symbol "c".

By rearranging Einstein's equation into M = E/c2 we see that M cannot be zero because c is a constant, and a photon has energy.

Here is the source of confusion. Mostly, you hear this equation described as the mass energy equivalence equation. If it is thought of as the relativistic mass energy equivalence equation then it makes it clear that something other than the Galilean definition of mass is being used.

Just to add a little more confusion back (you don't get anything for nothing), even the use of the term relativistic mass has been controversial. See this university page for more information.

E=Mc2 says that the relativistic mass of an object may be quantified in units of energy and vice versa. The conversion factor is c2. As energy is added to a system, that system's mass is increased. This implies that a stone would weigh more on Earth if it is heated up, and that is true. However, the difference would be insignificant.

Rest-mass is a property of an object which is measured to be the same value no matter what your frame of reference. Relativistic mass is not measured the same for all frames of reference. It comes into play when an object is moving, and is added to the rest-mass. At low speeds, relativistic mass has little effect, but at speeds approaching c, the effect is completely overwhelming.

The full equation which separates rest mass (mo) from that energy which is contributed by momentum (p) is:

E2 = mo2c4 + p2 v2

Clearly, if mo is zero, (as in the case of the photon) then v=c and E2 = 0+ p2 v2 which reduces to E=pv which makes sense because momentum times velocity is energy. Hence a photon has an energy. (It's proportional to frequency).

On the other hand, if mo is non-zero, then v cannot equal c. In this scenario, depending on the mass, and velocity, either term can dominate, or both can make a significant contribution.

An object with rest-mass that is moving near the speed of light - as in the case of an electron in a cathode-ray tube requires the rest-mass plus the relativistic mass of the electron to be used in ballistic calculations.

Many physicists prefer to avoid the confusion over mass by using only rest-mass, and noting that this is a property of the object itself which is measured to be invariant. That is, it has the same value to all observers regardless of their speed. Any energy added to a system is described in other terms than mass - such as momentum. This removes the confusion somewhat, but in popular texts, the term relativistic and rest-mass are here to stay.

I promised an alternate way to look at the constancy of light. Here it is:

The fact that a photon has no rest-mass means that it cannot be accelerated. Therefore is has to travel at c. So you cannot BOUNCE a photon, or 'give it a nudge', and if you do something to add more energy to it then its frequency changes but not its speed. For example, if you rush towards a photon, then it blue-shifts which means, for your frame of reference, it is a higher energy, and thus is more energetic. Conversely, if you back away from a photon then it red-shifts and looks like it has a lower frequency and less energy. When you make a torch shine, then you are creating a fresh photon which leave the torch at c until it bumps into something at which point it is absorbed. In transparent mediums like glass and air etc, the photons are mostly absorbed and re-emitted, usually with a different direction (scattering), perhaps with a significant colour when some frequencies are absorbed more easily. But in free space, we can think of the photon that you created as zipping off into space at c.

Let's stand on the ground and do this in a thought experiment. Stand on a moving walkway with a torch pointing forward. The photons are still leaving the torch at c. Now speed up the walkway incrementally for a moment and fall back to a constant, but greater velocity (relative to the people not on the walkway). The photons still leave the torch at c. Now imagine everything around you except the walkway to fade away so that you cannot detect anything except you, your walkway, the torch, and the light beam. Everything looks exactly as it did when you where stood firmly on the ground. You can't tell in your inertial frame whether you are moving or not. Now the walkway accelerates again - just a little. You can tell that happens because momentarily, you feel a as if a gravitational pull acted on your back. But when it settles down, your torch is still creating photons at c, and you can't tell whether you are moving or not. You can get 'boosted ' like this forever, and the torch still creates photons that leave at c. Time and motion look normal to you at all times that you are traveling at constant velocity. The people next to the walkway view a different scene though. They see you periodically accelerating towards the speed of light (in their frame of reference), but never actually reaching it. Your movements appear to them to slow down progressively.

The relativistic mass that we were talking of earlier is only of any importance to the people who are watching you on the walkway. Furthermore, if there were other walkways with people traveling on them and they could see you, their impression of you and your torch would be different in each case. But inside your inertial frame, everything is just sweet.

## Slow down, you move too fast, you got to make the morning last.

The tough question is "Why does light travel at a constant speed?". No one really knows. The speed of light may be expressed in terms of two other constants, but that does not really help you answer the question. The converse question is somewhat more revealing which is, "How could light travel at ANY speed?" If you heard that light must travel at a constant speed no matter the frame of reference and find it hard to swallow, then the consequences of imagining it to travel at any speed is preposterous. This would imply allowing to travel infinitely fast, or send a signal infinitely fast which is ridiculous in the extreme. Not only is the the very term, infinitely fast nonsensical, all you need to do is look at the night sky and ask, "If light traveled infinitely fast, then why am I not burned to a crisp from all the light arriving at me in zero time, and how silly is that anyway, and also why can I see the stars at all?". Everything that ever happened, and ever will happen would have already happened in literally no time. In this thought experiment, where light is allowed to travel at any speed, including infinite speed, there is no time, there are no events, there is no matter, there is nothing. So light MUST have a speed limit.

## If it has no rest-mass, It cannot rest!

Since a photon has no rest mass it can ONLY go at c (the speed of light), no faster, no slower. It cannot accelerate or decelerate. It can only be absorbed, or emitted upon interaction with an obstacle. I say this while also mindful of Feynman's highly successful theories about virtual particles, and what I am referring to is the average result of the speeds and trajectories of these virtual particles. I also say this knowing that a light-beam can be slowed down in a special gas at low temperatures to become stationary. However, this is an aggregate phenomenon where the light beam is contained in a small area. All the individual photons are still moving at c.

Remember: When energy is added to an object, that object has more relativistic mass.

To move an object, you must add energy to it. Even at low speeds, to accelerate an object, you must add more energy this moment than was added the previous moment.

Force = Mass X Acceleration

Velocity is meters per second.

Acceleration is the rate of change of velocity, and is therefore in units of (meters per second) per second.

But as an object approaches relativistic speeds compared to an observer in an inertial frame, it gains significantly more energy, and this compounds the problem of accelerating it further.  It's a problem which gets out of hand the faster you go, with the ultimate conclusion that an infinite energy would be required to accelerate a mass to c. Since infinite energy is not available, nothing with non-zero rest-mass can travel as fast as light.

An object is either massless and is emitted at the speed of light, or it has some rest mass and cannot reach or exceed the speed of light.

## Wacky hypothetical particles that can't slow down.

A Tachyon is a hypothetical particle with "imaginary" mass suffering the same kind of problem. It cannot be decelerated to the speed of light. These things appear in some serious theoretical frameworks - like the limited and outdated but interesting bosonic string theory which is a 26-dimensional theoretic playground. But because they cannot cross that same light speed barrier, we could not access even a localised Tachyon particle to transmit a signal faster than light. In any case, in the theories in which they present, they are highly unstable, and tend to ring alarm bells for the theory in play.

So all those Sci-Fi movies that use "Tachyon beams" to communicate across vast spaces are really pushing the envelope as it were.

## Gumby space

Bending space is fundamental to General Relativity (GR), and theoretically might be exploited to join two distant parts of the universe by folding space and punching a hole into it. But the amount of energy postulated to do such a thing is mind-blowing. Whether humans could ever do such a thing is very speculative. But even if this were possible, and we could join two distant regions of space though a wormhole or whatever you like to call it, we would not be required to exceed the speed of light to move through it.

We said earlier, that the dark night sky is a good reason to conclude that light has a speed limit. But it does not explain why the universe is gradually heating up to extreme limits, and therefore glowing at night as bright as our sun in the daytime. You see, since we strongly feel that there are either infinite stars out there, or certainly a mind-numbing large amount, and they are very very old. Anywhere you look in the night sky should coincide with billions of stars, and be very bright. "Space itself is expanding" and "Light takes significant time to get to us from the distance of the stars". This explains why most of the night sky is very dim despite the enormous number of stars beyond what we can see. Importantly, this also demands that the universe is not infinitely old. If it were, then even though light has a speed limit, there would be enough time for the night sky to glow brightly through the accumulation of photons from countless stars even though they are very far away.

## Is it possible to separate objects faster than c?

Yes!

Since space itself is expanding, two objects moving in opposite directions at near the speed of light could be separating faster than light could be sent between them. Faster than light signaling is not possible even in this mind-boggling scenario.

In fact, the traditional big-bang theory suffers some issues with observations of deep space. The cosmic background radiation is so incredibly uniform, that we theorize that the very first instant of the big-bang was followed by an incredible expansion rate.

Using the traditional theory of the big-bang, energy and information would have to be transported at about 100 times the speed of light in order to achieve uniformity, 300,000 years after the big bang. We actually observe the expansion of space still today, albeit at a much slower pace, but we never observe faster than light signaling. The cosmic background radiation does have some incredibly tiny fluctuations. If, instead of surmising that light traveled 100 times faster an instant after the big-bang, we modify the big bang theory to include a tremendous but brief inflation period, the level of uniformity is nicely explained, and the tiny fluctuations are explained.

Yet again, this is evidence that light has a speed limit.

Imagine two dots on a balloon. An ant tries to run from one to another as fast as it can. But someone blows up the balloon so fast that the dots move apart faster than the ant can run. If the ant's top-speed on the balloon was analogous to light-speed in our universe, then these dots move faster than ant speed, and we can see how expanding space can separate objects faster than the speed of light.

Now imagine a small balloon with a fluid surface, and suspended in the surface is a powder. It might be unevenly distributed, or concentrated on one spot - it does not matter much as the starting conditions are not particularly chosen. Given enough time, the powder might become uniformly distributed around the whole balloon, but this might take weeks or months, or not happen at all. Now imagine the experience of one ant at some point in the unevenly distributed powder. Someone comes along and blows the balloon up to the size of a large ocean liner so fast that it suddenly appears almost as a flat surface to the ant. All the powder in that particular area would, by virtue of the rapid expansion of that local area appear to the ant to be almost perfectly evenly distributed. This is a rough analogy to the observed distribution of cosmic background radiation today. The ant, like us, sees a world which appears special even though the starting conditions were not particularly conditioned.

## Do you think that some day we will break the light barrier?

See results without voting

## More by this Author

quicksand 7 years ago

Took the quiz got two wrong!

Hi Manna,

A photon maintains a constant velocity as it has zero mass. It is the mass that qualifies a particle to accelerate in the absence of resistance. Right? :)

Manna in the wild 7 years ago from Australia Author

Hi quicksand. Well done on the quiz! I have read your question several times, but do not understand where you are coming from. One of the objections to using the unit "mass" in relativistic calculations is that it either has to be taken in context to be an effect of relativity or that which is an intrinsic property of the object, or both and this is confusing. I tried to clear this up in the article. For this reason, you can, if desired, work with relativistic momentum. In Einstein's words: ""It is not good to introduce the concept of the mass of a moving body for which no clear definition can be given. It is better to introduce no other mass concept than the 'rest mass' m. Instead of introducing M it is better to mention the expression for the momentum and energy of a body in motion."

Having the intrinsic property of "rest-mass" makes it impossible to accelerate to c. The fact that a photon has no mass (at least we think it's a fact) means that the photon can only exist at c, and it is not possible to decelerate a massless particle. When a photon (which is a packet of energy) strikes an atom, that atom can absorb the photon. The atom will be upset by this change in energy and change it's configuration in a quantum change. That change in some cases will re-emit a new photon. In some chemistries, the incoming absorption could knock out an electron, and emit a photon at a different energy, but whatever happens, energy must be conserved which means that it cannot be created or destroyed.

You can find the relativistic momentum equation here : http://hyperphysics.phy-astr.gsu.edu/hbase/relativ...

If you try to re-phrase your question with this in mind I will do my best to answer.

quicksand 7 years ago

Hi Manna, The point I was trying to make is that acceleration is possible only if mass exists. Thus the photon having zero mass cannot accelerate. Therefore v=c or v=0 :)

Manna in the wild 7 years ago from Australia Author

Hi Quicksand. I agree. Intrinsic mass is a resistance to acceleration when a force is applied to it. If you like, you can imagine a tiny force applied to a tiny mass which would make it accelerate. If you halve the mass and the force and repeat the experiment, it would still have to accelerate. In the limit, the massless entity must move at maximum speed even when no force is applied.

jaildaar 7 years ago from New Delhi, India

Hi manna it seems you are quite energetic to write such a long post. I haven’t read it full but I definitely will as I get more time, but I want to ask something you said if you heat a stone it would weigh higher that is to say the rest mass of an object changes by giving energy ok. Now you know an electron is accelerated in an orbit and hence is a constant source of electromagnetic waves emitting out from it. Now here I want to ask why is the rest mass of electron not decreasing if it is emitting EM waves , that is why all electrons have same rest mass?

and I would like you to give views about other physics topics that I have written.

Manna in the wild 7 years ago from Australia Author

Hello jaildaar. Rest-mass is an intrinsic property of the stone and heating it will not increase the rest mass. However, since energy in Joules is converted to Kg when you multiply by a conversion factor of c-squared, then adding energy heats it up, and that increases the total Kg of the system. It is true there will be some radiation, but if the radiation was greater than the energy input, then the system would cool, not heat up. Of course, you could postulate that the stone is damp and porous and heating it will boil the water from it. This would release many times more mass than gained from energy added to it by heating it up. The effect that I describe with the stone is a theoretical tool. It would be difficult to actually measure.

An orbiting electron is fixed at a certain energy and does not constantly emit electromagnetic waves, it does not do "work" as it is in a constant energy state, and if it did lose energy, then it would fall into the nucleus and that does not happen. In order to emit electromagnetic waves, it needs to fall instantaneously to a lower energy band and this emits the energy, in the form of a photon. The photon is "born" traveling at c. It can only fall to a lower energy state if there is "room" energy-wise to accommodate it. Electrons are fermions, and as such cannot occupy the same quantum-state as another.

The following link will back this up: http://www.mikeblaber.org/oldwine/chm1045/notes/St...

It is one of the most concise and clear mathematical explanations I've seen.

All electrons are identical fundamental particles - that's why they have identical rest mass of 9.11 × 10?31 Kg- as does it's anti-particle, the positron.

A good way to view rest-mass is, "That property that makes the object resist acceleration".

I'd love to see what else you have written and will take a peek.

jaildaar 7 years ago from New Delhi, India

I completely agree to you , but I think I my question was not properly framed so you didn’t get it

What I meant was as you know acceleration is change in velocity divided by time taken. so keeping this in mind we can say that an electron is accelerated even if it moves in a circular motion ( although this concept is abandoned if quantum mechanics).

-And we know a change in Electric field produces a magnetic field and vice a versa.

-and an electron at rest emits electric field which is disturbed when it is accelerated, that is to say the change in electric field will definitely produce a magnetic field which will produce electric field and what we get is an Electromagnetic wave. Is it ok?

Now since the electron is responsible for production of this EM wave so there must be a loss in energy of the electron so where the energy came from ?

Manna in the wild 7 years ago from Australia Author

Hi - There are two issues I think. One is that the ballistic interpretation of electron motion about an atom is wrong enough to cause confusion. The other is that even in the simple Bohr model, the orbiting electron is at a fixed energy and a classical interpretation leads to problems as you suggest. You seem happy that QM abandons the orbiting model, and there is good reason for that. The Bohr model is incomplete. It's good enough for some useful calculations, but nevertheless not good enough to get a good grasp of what is going on or to explain things like quantum tunneling. The electron can be a bit like a little bullet but it is a wave, Or rather it was shown to be a wave, but it does bullet-like things too. This wave-particle duality is completely inconsistent with classical mechanics. The "orbiting" electron is, in QM replaced by a sort of 'probability cloud' as it never really has a definite place to call home.

There is a non-zero (but small) probability that an electron found normally mostly probably at some distance from the nucleus will be found inside the nucleus and captured in an atomic reaction. This can turn a proton into a neutron!

The other is that an electron (or it's charge in fact) at rest would not emit an EM field. It would be nice if it did because that would supply free energy. :-)

Your last paragraph exposes this flaw anyway.

jaildaar 7 years ago from New Delhi, India

I think this does not answer my question, i would appreciate if you would be a little precise and answer to the line of question. and I really don't know the answer thats why I am asking. but the rest you've told in your post I know a good deal of it.

Manna in the wild 7 years ago from Australia Author

OK - I am trying. :-) Perhaps I am having difficulty identifying the exact question. Perhaps line - by line might help...

"What I meant was as you know acceleration is change in velocity divided by time taken."

OK

"so keeping this in mind we can say that an electron is accelerated even if it moves in a circular motion"

I have a little problem with this for a QM description. It's a classical view which describes centripetal force.

" ( although this concept is abandoned if quantum mechanics)."

OK great.

"-And we know a change in Electric field produces a magnetic field and vice a versa."

I was not comfortable with this statement at first, I see what you are saying though: A charge at-rest has an electric field only. If moved, it produces a magnetic field too. Whether an observer experiences just the electric field or both depends upon their frame of reference. If you control and vary a magnetic field, then it will move a charge in it's presence, and conversely, a charge that is moved produces a magnetic field. Energy is not necessarily exchanged in this relationship.

"-and an electron at rest emits electric field which is disturbed when it is accelerated, that is to say the change in electric field will definitely produce a magnetic field which will produce electric field and what we get is an Electromagnetic wave. Is it ok?"

OK.

"Now since the electron is responsible for production of this EM wave so there must be a loss in energy of the electron so where the energy came from ?"

oooh, Unless you extract energy from the system, no work is done. In the case of an electron which is bound to an atom, it has a fixed, quantized energy which can only be changed if "work" is done - either by absorbing or emitting a photon. The electron is then bound to the atom at a different (quantized) energy level. The electron will try to fill the lowest energy slot available of course, but if all lower energy slots are taken, then it has to fill the next one higher. Electrons are fermions with fractional spin 1/2 as opposed to a photon being a boson (integer spin 1). Bosons can share states, while fermions are subject to the Pauli-exclusion principle.

If that helps - pls let me know. If not I might consult some others to see what I am missing. Oh - keep up the good work too - I read another of your hubs.

jaildaar 7 years ago from New Delhi, India

I think there is some concept missing in both of so i will consult somebody and clarify my doubt.

now see this you know that an electron at rest or in an inertial frame of reference have an electric field assosiated with it, now my point is electron must be getting something out of itself to produce it coz now the space-time surrounded by electron has the ability to do work. My question which variable is changing in the elecrton coz it is producing a change in the space-time surrounding it.

I dont know if you know but the cost which a celestrial object has to pay to produce gravitational field is mass.yes mass of heavenly bodies change with time, but the change is so small for Small masses that we have to take observations for heave masses such as a pair of huge blackholes rotating about themselves.

Manna in the wild 7 years ago from Australia Author

Ok - let me know what you find out. I can't see how the electron can get something out of itself. Its charge and mass are constants.

The quiz question that says "all of the above" for an answer is in error. You might say that evidence of light having a speed limit is that the sky appears dark to us from earth. However, the question implies that the appearance of the sky CAUSES ("...because...") light to have a speed limit.

thank you--that's 11 out of 11 for me now! :)

Manna in the wild 7 years ago from Australia Author

Thank you Chad. I will take a look at the wording.

hello dave 6 years ago

Interesting Hub, very informative.

Manna in the wild 6 years ago from Australia Author

Thank you "hello dave".

ss sneh 6 years ago from the Incredible India!

[Is it possible to separate objects faster than c? Yes! Since space itself is expanding, two objects moving in opposite directions at near the speed of light could be separating faster than light could be sent between them]

is actually wrong! The answer is NO

Imagine two twin brothers A and B traveling at the tips of two light beams propagating to two different directions, say north and south, starting from a single origin.

If A shows a torch light to his brother B, then would B see the torch light approaching to him at a velocity faster than "light's velocity"?

No. B will still see the torch light's velocity as c-300,000 km/s - constant lights velocity. That's the absoluteness of Light!

This absoluteness of light's velocity is the basis of special theory of relativity formulated by Einstein 105 years ago.

We do observe it in everyday life. Since universe is expanding, a galaxy that is 13billion light years away from our earth is indeed moving away from us at near the speed of light, but we still see light (radio waves) approaching to us from it at a constant velocity equals c.

* * * * * * *

Could we ever travel at the speed of light or faster than the speed of light?

Yes definitely!

In the quantum world, speed of light is not a BIG ISSUE!

Particles do communicate each other with infinite velocity even if they are separated by a huge distance.

Do you know we have already teleported a photon to 10 kilo meters away instantly?! -- Thanks

Manna in the wild 6 years ago from Australia Author

Thank you so much for your comments. May I refer also to

http://www.universetoday.com/2008/04/22/how-can-ga... and http://en.wikipedia.org/wiki/Faster-than-light ". It is thought that galaxies which are at a distance of more than about 14 billion light years from us today have a recession velocity which is faster than light." FLT signalling is not possible, so it would not be possible to see these galaxies. In your example, If A and B are moving apart near c but space is expanding between them such that their distances increase faster than c, then they will not be able to see each other's torches at all.

* * *

Even at quantum dimensions - as in the example of a tunnel diode FLT signalling is not possible. People get confused (understandably) what is going on here. You will read arguments that an electron can 'tunnel' through a barrier and seemingly appear before it enters. This fanciful explanation is confused by imagining the electron as a bullet-like object. It's better to consider the wave-like nature of the electron so that the wave-front emerges from the barrier before the peak enters the barrier. With this model it becomes more sensible. The point here is that energy is 'borrowed' from the quantum vacuum and later returned which allows an electron to pass through a barrier which would not be classically possible. Here is a good reference: http://enphy.zhetao.com/booksec.dep?op=list&v=vi&c...

And here is a reference with an outlandish opening statement: http://www.andersoninstitute.com/quantum-tunneling... where it states (incorrectly) "The correct wavelength combined with the proper tunnelling barrier makes it possible to pass signals faster than light, backwards in time." People get confused about this stuff.

In the quantum world we need to consider the continual appearance and disappearance of virtual particles and the effects of these are experimentally measurable. An *approximation* to the theory of quantum mechanics allows you to tentatively say, "the particles briefly and temporarily violate conservation of energy." But a rigorous treatment shows that conservation of energy is observed at all times. See http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Qua... for more in depth information. In this article, there is a good argument why FLT signalling is excluded despite a tantalizing suggestion that a virtual photon's plane wave is seemingly created everywhere in space at once, and destroyed all at once (thus ignoring c).

* * *

A teleported photon has indeed been experimentally verified. But yet again, FLT signalling is excluded from the system. You will find many ill-informed articles stating that we will be able to send signals faster than light, but this is wrong. I am working on another hub which explains Quantum Key Distribution, and this will explain why FLT signalling is not possible even with quantum entanglement. Hint: Heisenberg's uncertainty principle.

Allen 6 years ago

So, what about the Casimir effect? Removing the vacuum energy has been theorized to allow a photon to travel faster than c...

manna in the wild 6 years ago

Einstein's equations refer to inertial frames. If you are looking inside quantum processes, like the casimir effect, this is a different and very odd world. The following wiki article describes some of the controversy: http://en.wikipedia.org/wiki/Faster-than-light#Fas...

If forced to choose 'can photons travel faster than light' I still lean towards 'no'. In particular, I think the acid test is whether FLT signalling is possible, and there does not seem to be a way to do this.

The thing about quantum systems is how it is 'time symmetric' which means that any experiment you run forwards in time can be run backwards and you get the same initial conditions. Running 'time' backwards - whatever that might mean is akin to FLT. So you can find cases at dimensions where quantum effects dominate, and explain them using theories that allow photons etc to go faster than light. But a photon by the way has no rest mass, so this does not seem too crazy and you can theoretically have 'c' a little greater in the energy-depleted vacuum between the Casimir plates. But here we are dealing with virtual and massless particles - not things that you can accelerate.

Daniel V. 6 years ago from Romania

Truly mind-blowing, but you have made it easy to understand. Thank you and 'thumbs up'!

Manna in the wild 6 years ago from Australia Author

Thank you for your kind comment Daniel.

nickdevalda 6 years ago from swansea wales

excellent stuff!!!!!

Food for thought????

why is the speed of light seen as a magical speed?

we say nothing can go faster than the speed of light? Personally, I think thats rubbish.

the speed of light is constant when measured from a referential point, ie. the point of origin.

the speed cannot be universally constant as the universe is expanding, moving in every direction etc. it is simply not possible.

what im trying to get at, is that the speed of light is the speed of light, nothing more, nothing less, and its just a figure that us humans have been awestruck at for aeons, but, as with the sound barrier, we smashed it after a few attempts.

And as far as I know, Einsteins theory of relativity is based on a static universe, so, arent these just approximations?

Manna in the wild 6 years ago from Australia Author

Hello nickdevalda.

I don't think c is a magical speed. It's a numerical asymptote. The consequences of allowing information to travel at any speed leads to absurd results, so there has to be a maximum. (information by the way may be carried by a massless particle).

You are entitled to think what you like, but no one has found one jot of evidence that FLT signaling is possible.

The expansion of space does not affect the speed of light since space is not like a conveyor belt. It's possible for two objects to be separating greater than c if they are both high speed and space is expanding, but in that case signaling between the two is not possible.

The sound "barrier" is not a barrier. That's a fallacy. Sound is a pressure wave - a mechanical shock wave which moves through a medium. Light is energy which can travel in a vacuum.

Einstein's theory of relativity is most certainly not based on a static universe. Some solutions of the equations fit a static universe providing certain parameters take specific values.

peter nubile 5 years ago

if nothing can go faster than the speed of light,how can the C2 term be part of E=MC2

Manna in the wild 5 years ago from Australia Author

Hi Peter,

In E = MC^2 ( mass x "speed of light squared" ) consider C^2 to be nothing more than a number. It is a conversion factor and nothing more. This is why this equation is called the mass-energy equivalence equation. It states that mass and energy may be converted from one into another, and the conversion factor is ~(3x10^16).

Kirui 5 years ago

As far as i know equbtions equate only the amounts. So why don't you say: the amount of energy in an object is proportional to the amount of mass in that object?

Manna in the wild 5 years ago from Australia Author

That is a correct statement.

Kirui 5 years ago

Consider this concerning the 'constancy of the velocity of light'. It goes without saing that we are certain that a photon always travel at c. So we are always uncertain on its position in the univers. There remains a probability that at time t0, a photon will be located at x0. Where x0 is anywhere in the universe. At another time t1, there remain a probability that the photon will be found at location x1 where x1 is anywhere in the universe. So the difference x1-x0 is any value from negative infinity to positive infinity. Hence the velocity of the photon at interval t1-t0 is anywhere from negative infinity to positive infinity!

Manna in the wild 5 years ago from Australia Author

Hi Kirui, The problem is that 'at' the speed of light you lose any concept of a frame of reference so trying to make sense of 'space' at c leads to tears. It's kind of like worrying what 'North' means if you are stood AT the north pole.

Kirui 5 years ago

Let us then consider a velocity less than c call it v. Let us say we are certain at time t0 that an electron is traveling at v. Still, we will be uncertain of its exact location in the universe as per the uncertainity princible of quantum mechanics. There remains the probability of finding the electron at x0 where x0 is any distance from frame f. At time t1, we are certain that the electron is traveling at v still we are uncertain of the location of the electron. There remain the probability of finding the electron at point x1. Where x1 is any distance from f. Now the observer is in f. Hence he does not loss the concept of frame because the observer is stationary relative to f during period t0-t1. My question is simple. At what velocity do an electron move over a given time relative to f so that it can be found anywhere in the universe? The interval x0-x1 will be any distance no matter how large it is yet period t0-t1 is certain period. Musn't it travel faster than c for some probable interval x0-x1?

Manna in the wild 5 years ago from Australia Author

Kirui, I am very impressed especially if you worked that one out all by yourself. What you are referring to, I hinted at in the body of the article.

Each possible transition from A to B is called a history. Each history is qualitatively described by a complex number z called the individual transition amplitude indexed by i and written z_i.

This is a vector. The length of the vector is given by |z_i| which is simply the 'hypotenuse'. The square of this |z_i|^2 is the individual transition amplitude.

The sum of all individual transition amplitudes is the total transition amplitude or the sum over histories.

Take the absolute square of that and you get the total transition probability.

In this way, we have described not only a classical deterministic transition from a to b for minimum total system energy but also a quantum physics family of Markov stochastic histories which includes all possible routes from A to B. This includes continuous-time and discrete-time Markov chains. Since each give an equal contribution to the total transition probability, then we arrive at your conclusion that some of these routes involve faster than light 'travel'

BUT... You can't isolate one of these. These are theoretical tools and the net result remains that it is impossible to send a signal from A to B faster than light.

That was a bit heavy, and I hope I didn't muck it up.

Gary Shorthouse 5 years ago from Reading, UK

Another great read - a subject dear to me.

I am always fascinated by the concept that if we could sit on a photon, or a photon had conciousness, then we and the photon would have no experience of time. We could traverse the known universe in zero time, yet to an observer it would seem like 50 billion years or so.

In your opinion, would c necessarily have the same value in a different universe or, assuming the existence of a multiverse, is the value that we measure for c unique to our particular universe? Would the value for G be different too? Is there a relationship between c and G?

Now I really must go and get that beer.

Manna in the wild 5 years ago from Australia Author

Mathematically, its like asking you to stand AT the north pole and point north. There is nothing special about that point on the globe apart from axis of spin and magnetic north (which both change), it's just the coordinate system we use to locate points on the globe. If you rearranged latitude and longitude you could make London the most northern point on the globe. At least expeditions would be less traumatic (unless it's in the middle of the M25).

The many world theory just won't lie down. It seems to solve paradoxes in time travel for one thing. But if c was to change, this is to say that the fundamental constants of the fabric of space are different. There is no telling what that would do to the viability of a parallel universe. It might not survive more than a blink. But on the other hand, with an infinite permutation of fundamental parameters to choose from, you would have to conclude that just about anything is possible.

If the sun winked out instantaneously by getting sucked into a parallel universe or something, then you can calculate how long it would take for the planets to stop orbiting. This calculation uses the speed of light as the 'speed' of gravity. Gravity's effects happen at light-speed.

c is not special to light - it's the cosmic speed limit for information transfer.

Gary Shorthouse 5 years ago from Reading, UK

Thank you for taking the time to answer my queries.

I still have a problem accepting that constants such as c and G simply "are" and are truly universal.

Agreed that some solutions could create universes that blink out immediately, but others obviously create stable universes such as the one in which we exist. However many might fail does not preclude the number that succeed from being infinite; continuous inflation has always struck me as a cool concept.

Are the universal laws of physics truly universal and were they laid down at the instant of the big bang, or did they sort of evolve as the universe cooled down? In other words was, for instance, the strength of the weak force or the mass of a proton pre-determined by the big bang before either of them "condensed" from the milieu?

Manna in the wild 5 years ago from Australia Author

Hi Gary, You are not alone in wondering if the laws of physics are truly universal. If proven otherwise, it would be a massive shake-up for physics since this is axiomatic - at least for our observable universe.

But... take the fine structure constant as an example. This is an extremely well measured and calculated constant at the heart of Q.E.D. I read some time ago that there could be evidence this slightly changing over space-time. So I looked for an article on it and found this:

http://physicsworld.com/cws/article/news/43657

but it is a controversial result - even the comments in that article argue with the conclusion.

Kirui 5 years ago

I was thinking about this 'inability' to travell faster than light and I wondered why physicists don't say

APARENTLY, we cannot move faster than ligh. it goes this way; imagin that we were bats and could locate an object precisely by hearing a sound from it. So if a car is receeding away from you, to get the first location, a gun is fired in the car. After moving for some distance, another shot is fired and the bat will locate where the car was latter when the sound reaches him. Think about this, no matter how fast the car moves, the bat, using sound only can never measure and find the car to travel even at the speed of sound, let alone faster than the sound!

Think about this, it is logically imposible to measure and find a velocity receeding faster than the signal conveing the information about the position of a moving object! It is not physics, it is pure logics!

Kirui 5 years ago

Yes, bats measures and find the same velocity of sound for all observers in all frames! You can imagine how beings that can detect a hypothetical signal faster than light are laughing at men!

I can convince you that light ACTUALY takes the velocity of the source! a stationary observer measures and find everything in that frame, including light, as though it is happening slowlier. The whole story has nothing to do with space, time or even velocities! It is solely the moment in which nature reveals things in different frames!

Manna in the wild 5 years ago from Australia Author

Hi Kirui,

There is a huge difference between sound and light. Sound is a physical bumping of molecules that transfers energy from one to another kinetically. Light needs no medium to propagate. This was the purpose of the Michelson-Morley experiment in 1887. If bats did the equivalent of this experiment, then they would discover a "sonic" aether (the air). For light, there is no luminiferous aether.

Kirui 5 years ago

Michelson morley experiment assumed that if light propergates in ether, then light always donnot take the velocity of the source. The ether for sound is air molecules if bats measure the velocity of sound in a jet, they will not discover velocity difference because sound CAN take the velocity of the source. Are you sure that bats will discover air by mere measurement of velocities? Donnot assume other ways of discovering wind as in sence of touch. Ok, they will experice sonic boom for a coming plane. It can be interpreted as time stopping or time moving in revers by relativists bats! Remember that the only clock a bat has is a drum beat! Sonic boom comes because all drum beats are heard once. It has nothing to do with air! It has everything to do with the instance you perceive sound! A relativist bat can as well say it is all because the moving clock (drum beats) is halted relative to the stationary clock. Thus if the plane is aproaching you with the speed of sound, 'boom' is easily interparated as total time dillation by those who use drum beats as the only clocks!

Kirui 5 years ago

Know however that i am using sound as mere analogy. What i mean is that we must not necessarily experience events at the instnces of their ACTUAL happening. We can experience them even before they actualy happen! in frames of refferences receeding from each other, two similar drum beats will be heard each beating slowlier than the other (double effect in sound). the trick is the instance of actual happening and the instance of perception ('relativity' of simulteinity). we don't need even to mension time in the explanation! Think about it, how do we manage to observe a moving clock? Can we be certain of instance of actual happening?

Think about this; it is not that nothing can ACTUALY move faster than light. Rather, using 'signals' available so far, we cannot observe objects doing so! Consider very simple analogy; if an object moves at infinite speed from A to B, it will 'appear' like a piece of stick coming into into existence at once. But then if you are near A, you will see it moving at c from A to B and from B to A if you are near B because the signal at say B is taking time to reach you near A.

Manna in the wild 5 years ago from Australia Author

Kirui, You are certainly thinking hard about this. I hope to convince people of: no signal can exceed c, therefore no observable relativistic movement between two objects can exceed c.

example:

Two celestial objects can increase their distance faster than light can travel from one to the other but only because of the expansion of space. Since light from one cannot reach the other, no signaling takes place, and it is not observable.

Shaisty-Chase-Tea 5 years ago from The Outskirts

I have never seen a smart answer for this question... if a star is orbiting the black hole at a near speed of light velocity... does it project the light in front of it at a slower speed than the trail of light behind it... is a photon a particle? ...

if you are on the street and a car is aproaching, does the sound ring louder in front of the car than after it passes you... is light a wave?

what is the speed in which our vision reaches an object?

Shaisty-Chase-Tea 5 years ago from The Outskirts

I am Christian... Jesus said that we are "the light of this world" there fore and without a doubt, light must be a spiritual entity

Shaisty-Chase-Tea 5 years ago from The Outskirts

you got an 18% on your quiz according to mah's law

Manna in the wild 5 years ago from Australia Author

Hi Shaisty-Chase-Tea

"I have never seen a smart answer for this question... if a star is orbiting the black hole at a near speed of light velocity... does it project the light in front of it at a slower speed than the trail of light behind it"

No. photons always travel at c.

... is a photon a particle? ...

Yes.

if you are on the street and a car is aproaching, does the sound ring louder in front of the car than after it passes you"

Yes. This is the doppler effect and it happens because sound is a wave.

"... is light a wave?"

photons are particles that behave like waves. Welcome to the counter-intuitive world of quantum mechanics.

"what is the speed in which our vision reaches an object?"

Your vision does not travel. It is a product of photons landing on the retina, and then converted to electro-chemical impulses which are interpreted by the brain. This conversion takes a very long time compared to the speed of light.

Manna in the wild 5 years ago from Australia Author

I should also mention that you can detect the orbit of a star around a gravitational body because the trailing light as you put it will reach your detectors with a lower energy level, and the leading edge with a higher level. Lower energy light is a lower frequency (redder) and higher energy is higher frequency (bluer). So as you observe this star orbiting a black hole it will fade between red and blue each cycle. If you know what a wurlitzer organ sounds like, then a similar doppler effect would affect your orbiting star because of the wave-like behaviour of light.

Shaisty-Chase-Tea 5 years ago from The Outskirts

if it is a wave, then how do waves travel? i know that sound is in essence that act of vibrating particles of matter, explained easily by how a loud conversation is muffled by a wall in a house between two bedrooms... ... ... or a cheat hotel... ... ... but there needs to be a carrying substance for what we know as a sound wave... .... .... i am less certain of what the medium for radio frequencies but i suspect a carrier similar to static electro polorization of open air and house power for our electronic devices in electric currents ... ... ... i heard off a conducter that einstein tested to use static electricity generators that work like those things you touch at the gag shop at the malls that make electric bolts of blue and yellow and red touch your fingers but you don't feel anything, but on a larger scale.... ... .... is darkness the medium for photons? because they love to bounce off of everything to fill as much darkness as possible... ... ... and i see filling as space as the only property that could be considered parcitcularly particle-esque... ... ... however, if darkness is the medium, wouldn't that explain the reason we consider it particularly a sub atomic particle and not just an unknown known

Manna in the wild 5 years ago from Australia Author

Hi Shaisty-Chase-Tea,

There are only limited similarities between pressure waves in a medium (like sound) and that of the electromagnetic spectrum i.e. photons - the force-carrier for the electromagnetic force. The latter operates in free-space. It travels at maximum speed (c) in free space, and slower on-average in a medium (due to absorption and re-emission).

It is wrong to compare photons to vibrating particles like molecules. Don't try. It will lead to incorrect conclusions.

Darkness is not a medium.

Photons do not (in general) bounce. When a photon strikes an object (atom sized system) it is absorbed. The atom gains energy as a result, then relaxes and as it does so, emits a new photon. Again, travelling at c, but it is most likely at a new frequency. Since colour is frequency, this is what gives objects different colour. It's the photons that are re-emitted at new frequencies that present a new colour spectrum to your eye.

susannaisabeast 5 years ago

mana in the wild. you are a beast!

susannaisabeast 5 years ago

i got a 54% i failed! UH NUA!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! so how are you?

susannaisabeast 5 years ago

so are going to coment

Shaisty-Chase-Tea 5 years ago from The Outskirts

(c) of the sun and earth measured by the angle of the earth compared to the angle of the sun, vs when light breaks a straight horizen... ... ... seemed like a reasonable deduction... a theory based off of a common sense observasion for a rough estimate

Shaisty-Chase-Tea 5 years ago from The Outskirts

lol colors, einstein as a space trash junkie (space trash is poetry that has a complicated meaning)

Manna in the wild 5 years ago from Australia Author

susannaisabeast, 54% is a distinction. Nice work. ;-)

Owais Siddiqui 5 years ago

Manna 2 thoughts here:

1. Photon travels at c [the speed of light] what if further energy is injected will that effect its mass only or speed will also increase crossing the light speed barrier?

2. You mentioned that light has a constant speed but it abruptly drops to zero when it hits a black body and gets absorbed.

Manna in the wild 5 years ago from Australia Author

Owais Siddiqui

Hi. Thanks for reading so intently.

1. The relationship between a photon and energy is

E = hc/L

Where h is planck's constant, c is constant speed of light, L is the wavelength. Since h anc c are both constant, then

L is inversely proportional to E.

Therefore if you increase the photon energy, its wavelength goes down. This is why we say that short wavelength E.M. radiation is 'energetic'. Often, people talk about gamma rays being particularly energetic but the relationship holds for all of the spectrum.

2. a photon is massless. It either travels at c or it cannot exist as a photon. When it strikes another system its energy is transferred in total as a discreet quanta or not at all. An example might be to knock an electron into a higher energy orbit. The photon has then been absorbed into the energy of the electron. An electron has mass, so it can be accelerated. If that electron has the opportunity to drop to a lower energy state, then a photon is emitted. This is a direct consequence of the conservation law of energy.

Owais Siddiqui 5 years ago

Thanks for explaining

Manna in the wild 5 years ago from Australia Author

I guess everyone is following the FLT neutrino experiments (especially me!). I might need to re-write the hub!

ib radmasters 5 years ago from Southern California

Manna

I liked this hub, great job.

I didn't find the place where you mention the reason for squaring C.

Thanks.

Manna in the wild 5 years ago from Australia Author

"I didn't find the place where you mention the reason for squaring C"

That pops out in the derivation. To give a hint, think 'Pythagoras'. Look at eqn 1.4 and 1.5 in http://www.adamauton.com/warp/emc2.html

ib radmasters 5 years ago from Southern California

Manna

Thanks, that was a great site.

Amaan 4 years ago

Manna,

You are very well versed in your subject. Im impressed by the way to take time to reply so well, as well as be kind.. Hats off, respect you Sir. I have learnt a lot.

Manna in the wild 4 years ago from Australia Author

Thank you for the nice feedback Amaan.

Manna in the wild 4 years ago from Australia Author

It seems those pesky neutrinos do have to obey the law. Reports out now confirm the experiments were flawed.

professorcoban 4 years ago from Florida

There is something you are forgetting: c is the constant for the speed of light in a vacuum. This is important for a few reasons. There is no such thing as a perfect vacuum, except in theory. Even interstellar space has radiation, virtual particles, and so forth. The temperature due to the Cosmic Microwave Background Radiation is about 2.7 above absolute zero, meaning that there is thermal motion, which means there is something there, i.e. not a vacuum. The disparity of vacuum energy is one of the main issues between quantum mechanics and relativity. Light is refracted because it changes speed. As you might know, a change in speed is acceleration (which you vehemently claimed that light could not do). Refraction is observed constantly, so there is no way to claim that it does not happen. It is possible to exceed the velocity of light within a particular medium. When a charged particle does this, it produces Cherenkov radiation. One of the theories about motion involves spacetime. Essentially, the maximum velocity through spacetime is 299,792,458 m/s. Since light travels that velocity (or close to it) in space, it experience no (or very little) travel through time. This is an explanation for relativistic time dilations. Basically, the faster an object/particle travels through space, the less it travels through time. Of course, this is all related through local gauge symmetries and inertial reference frames.

Manna in the wild 4 years ago from Australia Author

professorcoban I like your observations and comment. But the density of matter in interstellar space is small enough that at some scale there is nothing for a photon to bump into. I don't think I forget for a moment that c is the speed of light in a vacuum, in fact, in an earlier comment I referred to c as theoretical asymptote for any particle with mass. The only logical conclusion for a massless particle (before a collision) is that it travels at c. And yes - due to time dilation, 'time' has no meaning for a massless particle because there is no mass and no 'clock'. I sense that you are thinking in terms of light beams where I am thinking at the level of an individual photon. Nothing in your comment is wrong we are just approaching this from a slightly different perspective. Light *beams* are refracted because of a change in speed, but the individual photons are absorbed and re-emitted. You are talking about aggregate, and I am talking about the individual photon.

I really appreciate your observations. Thank you.

theorist 4 years ago

Suppose earth is moving away from some distant star because of the expansion of space. Should the rate of expansion reach c, the frequency of light from that star (when viewed from earth) is Doppler-shifted to zero, rendering the star invisible to us, thus explaining why we can receive no information from it. [Is this explanation correct? Further, is it specifically correct that lightspeed expansion is sufficient to render the star invisible, or must it be FTL?]

Anyways, here's my principal question: what happens when the space about us is instead *compressing* at c? Does the Doppler shift cause the frequency of the CMB to diverge, meaning we (and everything else) would be reduced to whatever the most elementary particles are? And is there any physical difference between what we would experience if the space around us were compressing at c, vs. if the compression were FTL? Or is the FTL (or even lightspeed) compression of space prohibited in a way that FTL expansion is not (by the divergence in the photon pressure, perhaps)?

Thanks!

Manna in the wild 4 years ago from Australia Author

Light-speed expansion of space or greater would render the star invisible.

It's nothing to do with Doppler shift that it would be invisible, it's just that light could not keep up.

Your second question is a good one and I honestly don't know. It's worth a bit of thought. Maybe you can find a good physics forum, ask that question and let me know.

theorist 4 years ago

Alas, it seems to indicate that my ideas about FTL expansion (even that FTL expansion would make a star invisible) may be an oversimplification (" For one fairly natural definition of velocity, there are galaxies we observe that are now and always have been receding from us at a velocity greater than c") (I'd be interested to hear you thoughts on this), suggesting that my corresponding question about FTL contraction may need some work before I submit it. But I'll give it a shot and let you know.

Manna in the wild 4 years ago from Australia Author

Hi 'Theorist' I'm definitely sympathetic to the content of the link you gave - particularly the lament about what it actually means to say 'faster than c'

This link: https://www.e-education.psu.edu/astro801/content/l... copes nicely with the issue by saying 'apparent velocity' when applied to the concept of distance between two points in an expanding region of the universe.

I can see why we can observe two distant galaxies that appear to separate faster than c (to us), but if you were in one of those galaxies the measurements would be as per GR.

... and now I must say that I've generated some doubt about the 'invisibilty' idea except that we do have that issue with the hubble horizon - i.e. can't see what is beyond it (without waiting - since it too expands).

It's easy to get confused with this stuff.

Manna in the wild 4 years ago from Australia Author

Manna in the wild 4 years ago from Australia Author

A great source of FLT information is here http://math.ucr.edu/home/baez/physics/Relativity/S...

theorist 4 years ago

Thanks, I'll definitely look though these.

abinash raj 4 years ago

nothing is impossible...........one fine day we would also travel in a light speed

Manna in the wild 4 years ago from Australia Author

How can nothing be impossible?