Speed of light is limited by what?

[Bobby]

The thing to understand is tha c isn't just the speed of light it is a property of space-time. Light doesn't "just happen to be the fastest thing we know", light is just one of the massless things we know of.

 

 

I've always had a problem with the idea that light has no mass. Light has momentum, light has a physical force (as in solar wind sails to prople a spaceship), light and mass can each create the other. I have always liked the saying "If it looks like a rose and smells like a rose and has thorns, it is probably a rose."

[Erasmus00]

I've always had a problem with the idea that light has no mass. Light has momentum, light has a physical force (as in solar wind sails to prople a spaceship), light and mass can each create the other. I have always liked the saying "If it looks like a rose and smells like a rose and has thorns, it is probably a rose."

 

Except you can accelerate or decellerate things with mass. You can't do that with light.

-Will

[Bobby]

Except you can accelerate or decellerate things with mass. You can't do that with light.

-Will

 

Your answer is reasonable, but it only adds to my unwillingness to assign mass to light.

 

A body at rest will remain at rest, and a body in motion will continue in motion ulnless acted upon by a force. - Newton's first law of motion.

 

If a spaceship is being acellerated by a solar sail, the opposite reaction is a change in the wavelength and frequency of the light. You can also look at it as if the spaceshiip is being propelled by photons, and the energy imparted to the spaceship is balanced by an energy loss by the photons.

 

Any action attributed to energy can always be attributed to mass, as can the reverse.

[Erasmus00]

Any action attributed to energy can always be attributed to mass, as can the reverse.

 

Thats not true. Look at light: light does many things as a virtue of its having energy. However, it has no inertial mass, you cannot accelerate it.

-Will

[Bobby]

Thats not true. Look at light: light does many things as a virtue of its having energy. However, it has no inertial mass, you cannot accelerate it.

-Will

 

This is leading to things I did not mean to stir up. Whether or not light has mass depends on how you want to define it. If I take flour, water, sugar, and a few other things and bake a cake, the flour, water, sugar, etc. did not go away, it is still there in the cake. If I take the cake and soak it in water it will come apart into flour, water, and sugar.

 

If the definition of acelleration is an increase in velocity, and if the definition of velocity is dstance/time, and if time slows down in a gravitational field, then light is acellerated by a gravitational field.

[Erasmus00]

If the definition of acelleration is an increase in velocity, and if the definition of velocity is dstance/time, and if time slows down in a gravitational field, then light is acellerated by a gravitational field.

 

That simply isn't true. Locally, GR becomes SR, and light is a constant. In other words, light is not accelerated by a gravitational field. It can be deflected (so called gravitational lens) but it always travels with the same velocity.

-Will

[Bobby]

That simply isn't true. Locally, GR becomes SR, and light is a constant. In other words, light is not accelerated by a gravitational field. It can be deflected (so called gravitational lens) but it always travels with the same velocity.

-Will

 

 

What part of it isn't true?

 

From Fundamentals of College Physics by Peter J Nolan, published by Wm. C. Brown Publishers - In 1905, Albert Einstein formulated his Special or Restricted Theory of Relativity in terms of two postulates.

 

Postulate 1 : The laws of Physics have the same form in all frames of reference moving at a constant velocity with respect to one another.

 

Postulate 2 : The speed of light in free space has the same value for all observers, regardless of their state of motion.

 

 

From Modern Physics by Frank J. Blatt published by MeGraw-Hill, Inc.

 

Talking about the Miscaelson Morley experiments.

 

The central problem, as Einstein perceived it, had little to do with the existance of an ether, but hinged on the principle of relativity.

 

THE LAWS OF NATURE ARE THE SAME IN ALL INERTIAL REFERENCE FRAMES

 

Einstein therefore proceeded from the following two basic postulates.

 

1. The principal of relativity is valid for all natural events.

 

2. The speed of light in vacuum, as measured in any inertial reference frame, is C regardless of the motion of the light source relative to that reference frame.

 

 

 

The point is that the measured value for the speed of light is the same for all inertial reference frames. It does not say that the speed of light is constant. It says that if observer A, using CA and RA measures the speed of light he will get C, and if observer B, moving at a constant rate relative to observer A, uses clocks CB and rulersRB he will also get C. Nowhere does it say that clock CA is running at the same rate as clock CB and nowhere does it same that ruler RA is the same length as ruler RB.

[Erasmus00]

What part of it isn't true?

The point is that the measured value for the speed of light is the same for all inertial reference frames. It does not say that the speed of light is constant. It says that if observer A, using CA and RA measures the speed of light he will get C, and if observer B, moving at a constant rate relative to observer A, uses clocks CB and rulersRB he will also get C. Nowhere does it say that clock CA is running at the same rate as clock CB and nowhere does it same that ruler RA is the same length as ruler RB.

 

The measured value for the speed of light is the same for all inertial frames, as you say. How then can light accelerate? It is always measured (by everyone) to move at speed c, as you say.

-Will

[Qfwfq]

Mass is energy, but energy isn't always mass. In 20th century physics, 'mass' is viewed as meaning rest energy. The energy of a photon is purely kinetic and this confines its kinematics to the light-cone. The best way to understand properly is by knowing the Lorentz-covariant 4-vector formulation of dynamics. Without this, there isn't much hope to make sense of the matter. Minkowsi gave the key to making sense of Einstein's insight.

 

If I take the cake and soak it in water it will come apart into flour, water, and sugar.

Are you quite sure?

 

Many of the atoms have formed different substances after baking.

[alxian]

some facts after reading this thread

 

 

light has no mass

 

the solar wind when interacting with a magnetic field discharges

 

light when passing through a magnetic fields alters its course

 

(is there then some slowing of the light? where does the energy go? what energy is given off to alter the lights course? is it turned into something like radiation, electricity, does that energy strengthen or weaken the magnetic field?)(i don't think the interaction is so perfect that light wave simply curves around the gravity well without leaving some tiny amount of energy behind. travelling at less than c)

 

light can impart a force on objects with mass

 

light has quantifiable and not negligable amounts of energy

 

light travels at c in vacuum but can be slowed and accelerated in some situations

 

 

light may not have inertia as it applies to matter but it can be slowed and then accelerated once more, and even become faster than c, but only with the addition of more energy.

 

matter is enery is an interesting argument, can all matter be converted into energy? once transformed is it posible to reconstitue matter from that energy? this would allow for such things as perfect teleportation in such that the matter remains constant you're not creating matter from stores of energy on the recieving end, you are transmitting energy at the speed of c from point a to b, however this percludes instantinaity, unless that maximum C can be transcended, by amplifying the light speed, without losing the ability to later reconstitute the matter latter.

 

question

 

if such a transporter were possible and you tried to transport a brain, would it remain conscious during the transit, if not would it be able to regain consciousness after reconstitution, you'd be freezing its operation temporarily but disintegrating it.

 

can a complex organic system like a brain survive such a process?

 

like, if you froze a living brain in nitrogen (something less barbaric i'm sure) and split it into a thousand pieces and them put them back together reconnecting each axon with quantum precision, would that brain once thawed be able to reawaken?

 

upon reconstitution it physically would be able to support the processes required to reawaken consciouness. like going to sleep or more acurately physically dying, no more electrical activity in the brain, it can be reawakened and those people are perfectly fine. unless electricity isn't the fundamental process in consciouness.. some other form of energy coursing through our minds below that threshhold.

[Bobby]

The measured value for the speed of light is the same for all inertial frames, as you say. How then can light accelerate? It is always measured (by everyone) to move at speed c, as you say.

-Will

 

Because of the way I defined acceleration. If acceleration is defined in terms of time and distance, and if time and distance change then velocity changes which is acceleration.

 

If it appears that I am playing with words, it isn't intentional. For many years I have had a burning desire to understand space, time, and gravity. So many things seem to depend on how you want to look at them. Perhaps I want to know what "really" is happening when there is no "really".

[coldcreation]

Because of the way I defined acceleration. If acceleration is defined in terms of time and distance, and if time and distance change then velocity changes which is acceleration.

 

If it appears that I am playing with words, it isn't intentional. For many years I have had a burning desire to understand space, time, and gravity. So many things seem to depend on how you want to look at them. Perhaps I want to know what "really" is happening when there is no "really".

 

Rest assured Bobby. Don't complicate things. Light cannot be accelerated faster than c. Read general relativity a few times, by Einstein himself, no some interpretation of it. Though I've heard Bertrand Russel wrote a great interpretation of relativity. There is a book, by the way, called Space, Time and Gravitation (by Eddington I believe). I have yet to fing it. Einstein was convinced that all physical reality could be eventually explained, that it waswithin our powers to find the solutions that would explain all physical phenomena.

 

I agree.

 

Coldcreation

 

PS. I can't look now but someone already answered the question of why the speed of light is limited: because of Minkowski spacetime. I re-agree

[EWright]

(is there then some slowing of the light? where does the energy go? what energy is given off to alter the lights course? is it turned into something like radiation, electricity, does that energy strengthen or weaken the magnetic field?)(i don't think the interaction is so perfect that light wave simply curves around the gravity well without leaving some tiny amount of energy behind. travelling at less than c) [/Quote]

 

Huh!? light IS radiation and it IS electromagnetic energy. So no, it would not be "turned into" something like that. If it loses energy it will either be given off as heat or as a change in the wave length/frequency relationship. It need not travel at less than c as a result.

 

light travels at c in vacuum but can be slowed and accelerated in some situations. light may not have inertia as it applies to matter but it can be slowed and then accelerated once more, and even become faster than c, but only with the addition of more energy. [/Quote]

 

Huh!? In what cases is light accelerated as faster than c by adding more energy? Light can slow when it travels through a medium such as water or glass, and granted it will then resume it's normal speed when it exits this material (if you want to call that accelerating), but SR says it is not accelerated faster than c. I do recall erading an article in which either light or a particle (probably light) was briefly accelerated faster than c for a very short distance; but I believe there is question about whether is was interpreted correctly?

 

 

Bobby, as for your description relating light speed in a gravitational field, I don't think you are correct according to Relativity. Relativity warps anything and everything, including space, time and reality, to MAKE light travel at the same speed relative to any observer. The speed of light as a constant is the primary postulate with the theory, so your description doesn't change the speed of light becuse relativity will warp your description to make it relative to light still traveling at c. :hihi:

 

For clarification sake, I am saying what relativity says/does here. I do not agree that relativy is 100% accurate in this way.

[Bobby]

Mass is energy, but energy isn't always mass. In 20th century physics, 'mass' is viewed as meaning rest energy. The energy of a photon is purely kinetic and this confines its kinematics to the light-cone. The best way to understand properly is by knowing the Lorentz-covariant 4-vector formulation of dynamics. Without this, there isn't much hope to make sense of the matter. Minkowsi gave the key to making sense of Einstein's insight.

 

 

Don't try to talk down to me, ding-a-ling. What part of Lorentz covariant 4 vector formulation of dynamics, light cones, and Minkowski do you not understand? Perhaps I can help.

[EWright]

:hihi:

[Erasmus00]

Because of the way I defined acceleration. If acceleration is defined in terms of time and distance, and if time and distance change then velocity changes which is acceleration.

 

Acceleration is always defined by the rate in change of velocity with respect to time. (or the second derivative of position with respect to time). Because the speed of light is always a constant, the derivative of the speed of light is always 0. Light does not accelerate.

-Will

[Bobby]

some facts after reading this thread

 

 

light has no mass =====> Text book answer - All mass can be converted to energy and energy can be converted to mass. Light is usually thought of as having no rest mass. This is not a problem because light can never be at rest.

 

 

I don't like this answer. If energy can become mass then where did the characteristics of mass come from if not from the energy? Mass is frequently thought of as "frozen" energy or concentrated energy. In my opinion if you freeze water, the ice is still water.

 

 

In short, it depends of how you want to look at it.

 

 

 

 

 

the solar wind when interacting with a magnetic field discharges =====> If light meets a magnetic field, the direction of the light will change. Magnetism changes direction only. Magnetism does not impart or take away energy.

 

 

light when passing through a magnetic fields alters its course =====> Yes

 

 

(is there then some slowing of the light? where does the energy go? what energy is given off to alter the lights course? is it turned into something like radiation, electricity, does that energy strengthen or weaken the magnetic field?)(i don't think the interaction is so perfect that light wave simply curves around the gravity well without leaving some tiny amount of energy behind. travelling at less than c) =====> There is a thing called the gravitational red shift. This can be explained in two ways. ( 1 ) The shift is a result of the slowing of light in a gravitational field and ( 2 ) the shift is caused by the light photons losing energy.

Since the energy od a photon depends on its wavelength and frequency, ( 1 ) and ( 2) above are mathematically equal. By convention, option ( 1 ) is usually preferred over option ( 2 )

 

 

 

 

light can impart a force on objects with mass =====> Yes.

 

 

light has quantifiable and not negligable amounts of energy =====> No. The energy depends on the wave length and frequency of the light. Very, very short wavelengths in the gamma ray part of tge spectrum has a lot of energy. Longer wave length such as radio waves also have a lot of energy, but the energy is spread out over a long (relatively speaking) distance.

 

 

 

light travels at c in vacuum but can be slowed and accelerated in some situations -=====> That depends on your definition of acceleration. Acceleration is usually thought of as a change in velocity. According to this definition light is accelerated when it moves from one medium to another such as from air to water. By similar logic, if time is affected by gravity then, IMO,gravity accelerates light.

 

 

 

light may not have inertia =====> Inertia is usually accociated with mass and light is usually considered to not be mass, therefore light does not have inertia. Light, however, does have momentum and acts like a force (I.E. space sails).

 

 

as it applies to matter but it can be slowed and then accelerated once more, =====>

See above. Depends on how you want to look at it.

 

 

 

and even become faster than c, but only with the addition of more energy. =====> I don't think so. Actually, I don't think you can add energy to light, but if you could you would change the wavelength and frequency, not the speed.

 

 

matter is enery is an interesting argument, can all matter be converted into energy? once transformed is it posible to reconstitue matter from that energy? =====> Yes and Yes

 

 

 

this would allow for such things as perfect teleportation in such that the matter remains constant you're not creating matter from stores of energy on the recieving end, you are transmitting energy at the speed of c from point a to b, however this percludes instantinaity, unless that maximum C can be transcended, by amplifying the light speed, without losing the ability to later reconstitute the matter latter. =====> I doubt that Scotty will be beamed up in the near future.

 

 

 

 

question

 

if such a transporter were possible and you tried to transport a brain, would it remain conscious during the transit, if not would it be able to regain consciousness after reconstitution, you'd be freezing its operation temporarily but disintegrating it. =====> Don't know

 

can a complex organic system like a brain survive such a process? =====> Don't know.

 

 

 

like, if you froze a living brain in nitrogen (something less barbaric i'm sure) and split it into a thousand pieces and them put them back together reconnecting each axon with quantum precision, would that brain once thawed be able to reawaken? =====> Don't know

 

upon reconstitution it physically would be able to support the processes required to reawaken consciouness. like going to sleep or more acurately physically dying, no more electrical activity in the brain, it can be reawakened and those people are perfectly fine. unless electricity isn't the fundamental process in consciouness.. some other form of energy coursing through our minds below that threshhold. ======> Don't know.