Faster than light

Corkscrewkenny

I'm an enthusiastic but uneducated, amateur theoretical physicist

If, THEORETICALLY, a pole made of, say, neutron star material was constructed and reached from earth to Proxima Centauri (4.2 light years away) and if the earth end was pushed, would someone at the Proxima Centauri end feel the result of the push almost instantaneously. THEREFORE can information move faster than light?

Rubecula

I can't say for certain, but I assume there would have to be a pressure wave travelling along the pole, and there would be an upper limit to the speed that this pressure wave could travel.

However if an object travelled around the sun at an orbital velocity of light speed. Would it's shadow at twice the distance travel at twice light speed?

If so (as nothing is actually moving in it's shadow) could shadowing be a binary system of info faster than light?

Morbert

Rubecula wrote: »

I can't say for certain, but I assume there would have to be a pressure wave travelling along the pole, and there would be an upper limit to the speed that this pressure wave could travel.

Yes, the information could not reach the other end of the rod instantaneously, and instead must be transmitted at sub-light speed.

However if an object travelled around the sun at an orbital velocity of light speed. Would it's shadow at twice the distance travel at twice light speed?

The shadow would 'travel' at twice the speed of light, but it is important to remember that no travelling is actually being done. Instead, photons are being intercepted by the object, causing the remaining photons to produce a pattern that our brain interprets as a "moving shadow".

If so (as nothing is actually moving in it's shadow) could shadowing be a binary system of info faster than light?

It could not unfortunately be used to transmit info faster than light. The shadow, although 'moving' faster than light, could not be used to signal faster than light.

gentillabdulla

The shadow isn't traveling.

Like darkness a shadow isn't an actual thing.

A shadow is just created by an object blocking the light.

Sorry the shadows aren't moving (In a physical sense) and cannot be used in this way to transmit information faster than light.

Basically what Morbert said.

Capt'n Midnight

check out the speed of gravity

also there is the slight problem of how you move a neutron star fast enough to create a noticable effect

Corkscrewkenny

Rubecula wrote: »

I can't say for certain, but I assume there would have to be a pressure wave travelling along the pole, and there would be an upper limit to the speed that this pressure wave could travel.

However if an object travelled around the sun at an orbital velocity of light speed. Would it's shadow at twice the distance travel at twice light speed?

If so (as nothing is actually moving in it's shadow) could shadowing be a binary system of info faster than light?

Good point. Pressure waves. But my whole idea is that waves aren't involved, whether light waves, radio waves, x rays or anything else. The whole process would be mechanical.

To take it to the extreme, a pole made of the most fundamental, densest particals in existence (say singularities at the centre of black holes) all in perfect alignment, all touching, no friction. To push this pole you have available all the energy contained in the milky way galaxy. THEN would the effect on Proxima Centauri be felt before a light beam could get there. THEORETICALLY.

I'll try and answer my own question with 2 points

1. String theorists might say that there would still be a wave because some of the particals would move in and out of dimensions 5 to 11 before pushing the partical next to them.

2. I think the way electricity works is by electrons pushing each other along a copper wire rather than actually travelling along the wire, so (if I'm correct) this is an example of fairly fundamental particles pushing each other as described in the original question. I don't actually know what speed electricity travels at.

Another good idea, shadows. I would guess relativity would come in here to prevent the shadow moving faster than light, ie time rates would be different between the orbiting object and the observer of the shadow.

Anyway, I still think the "pole" idea has some legs.

Offy

Corkscrewkenny wrote: »

Good point. Pressure waves. But my whole idea is that waves aren't involved, whether light waves, radio waves, x rays or anything else. The whole process would be mechanical.

To take it to the extreme, a pole made of the most fundamental, densest particals in existence (say singularities at the centre of black holes) all in perfect alignment, all touching, no friction. To push this pole you have available all the energy contained in the milky way galaxy. THEN would the effect on Proxima Centauri be felt before a light beam could get there. THEORETICALLY.

I'll try and answer my own question with 2 points

1. String theorists might say that there would still be a wave because some of the particals would move in and out of dimensions 5 to 11 before pushing the partical next to them.

2. I think the way electricity works is by electrons pushing each other along a copper wire rather than actually travelling along the wire, so (if I'm correct) this is an example of fairly fundamental particles pushing each other as described in the original question. I don't actually know what speed electricity travels at.

Another good idea, shadows. I would guess relativity would come in here to prevent the shadow moving faster than light, ie time rates would be different between the orbiting object and the observer of the shadow.

Anyway, I still think the "pole" idea has some legs.

Does any of the above matter? You would have to push the pole faster than the speed of light for it to arrive before its image. Is it possible for a physical object to arrive at a destination before its image does? Does that answer your question? No its not possible but as soon as you can move matter faster than the speed of light it becomes possible I guess.

rccaulfield

How could you move anything with that kind of mass? Its not a realistic situation or close imo.

mikhail

Corkscrewkenny wrote: »

I think the way electricity works is by electrons pushing each other along a copper wire rather than actually travelling along the wire, so (if I'm correct) this is an example of fairly fundamental particles pushing each other as described in the original question.

Electrons move relatively slowly in a e-m field. The electrons aren't pushing anything. I don't think this example is relevant the the question.

I don't actually know what speed electricity travels at.

The e-field travels at nearly c; depends on the material.

Offy wrote: »

Does any of the above matter? You would have to push the pole faster than the speed of light for it to arrive before its image. Is it possible for a physical object to arrive at a destination before its image does? Does that answer your question? No its not possible but as soon as you can move matter faster than the speed of light it becomes possible I guess.

Your reasoning is rubbish. Imagine a perfectly inelastic, massless pole. I push one end. The other end moves in unison with it. So the far end of the pole doesn't arrive before its own image, but if it's long enough, it arrives before the image of my end.

I guess this has to fall down on the "perfectly inelastic, massless pole." There's just no such thing.

Corkscrewkenny

mikhail wrote: »

Electrons move relatively slowly in a e-m field. The electrons aren't pushing anything. I don't think this example is relevant the the question.


The e-field travels at nearly c; depends on the material.


Your reasoning is rubbish. Imagine a perfectly inelastic, massless pole. I push one end. The other end moves in unison with it. So the far end of the pole doesn't arrive before its own image, but if it's long enough, it arrives before the image of my end.

Thanks mikhail, I think you're supporting me. In the scenario no matter travels any more than a centimetre, but information travels faster than light, the information being "There is something at the other end of this pole that has pushed it.

I guess this has to fall down on the "perfectly inelastic, massless pole." There's just no such thing.

I'm talking theoretically, not practically. The "pole" doesn't have to be massless if you have the energy of (say) a million Milkey Way galaxies at your disposal, does it?.

As to whether perfectly inelastic, uncompressable particals of sub-atomic matter exist or can exist, and whether these particles could live for long enough and whether there properties would allow them to touch, I don't know. Despite my best efforts, quantum mechanics is still completely incomprehensible and counter-intuitive to me.

Anyway, the bottom line seems to be that even information cannot move through spacetime faster than the speed of light (but I'm still not convinced).

mikhail

Corkscrewkenny wrote: »

Thanks mikhail, I think you're supporting me.

I think you have an interesting question.

I think the answer is no, but I don't know the physics describing how force is transferred along a pole. I fully expect that there's a theoretical upper limit on the elasticity of a material such that the pressure wave travelling along it is limited to c.

BTW, yes, it doesn't need to be massless, but if it wasn't, it'd be subject to enormous gravitational forces. Not important in a theoretical discussion, I guess.

thirtythirty

I've thought about faster than light before too - but i'm no scientist, so have no idea of the answer. But humour me for a second.

My understanding is that gravity attracts mass at a set speed. But on earth, things reach terminal velocity due to wind resistance. So, if you were in space where there was no resistance, you'd just keep accelerating. Is that right?

If so, what if you built a ship that had two extendable arms out in front of it (or something), and it could generate a gravitational pull in front of itself.

Presumably, the ship would just continually accelerate, because the the gravitational pull is always the same distance and same force, with no opposing resistance (like wind). So surely the ship would just keep going faster and faster, eventually beyond the speed of light.

As i said, im no scientist, but im pretty sure my theory is flawless!

spottyelephant

spottyelephant wrote: »

Presumably, the ship would just continually accelerate, because the the gravitational pull is always the same distance and same force, with no opposing resistance (like wind). So surely the ship would just keep going faster and faster, eventually beyond the speed of light.

As i said, im no scientist, but im pretty sure my theory is flawless!

It would gain mass as it accelerates. takes an infinite amount of energy to accelerate an object with nonzero rest mass to the speed of light

thirtythirty

bluewolf wrote: »

It would gain mass as it accelerates. takes an infinite amount of energy to accelerate an object with nonzero rest mass to the speed of light

Really?

Imagine:
Ship (1 tonne), Gravity (2 miles/second).

Now if gravitational acceleration is always constant, the ship should only ever weigh e.g. 1.5 tonnes, no matter what speed it's travelling at.

Speed = 0, pulled by 2 miles/second gravity; ship adds 0.5 tonnes to weight.
Speed = 100, pulled by 2 miles/second gravity; ship should still only weigh 0.5 tonnes more, because speed of "100" is exactly the same as "0", cuz it has the same gravity pull acceleration.

No?

Morbert

Corkscrewkenny wrote: »

Good point. Pressure waves. But my whole idea is that waves aren't involved, whether light waves, radio waves, x rays or anything else. The whole process would be mechanical.

To take it to the extreme, a pole made of the most fundamental, densest particals in existence (say singularities at the centre of black holes) all in perfect alignment, all touching, no friction. To push this pole you have available all the energy contained in the milky way galaxy. THEN would the effect on Proxima Centauri be felt before a light beam could get there. THEORETICALLY.

I'll try and answer my own question with 2 points

1. String theorists might say that there would still be a wave because some of the particals would move in and out of dimensions 5 to 11 before pushing the partical next to them.

2. I think the way electricity works is by electrons pushing each other along a copper wire rather than actually travelling along the wire, so (if I'm correct) this is an example of fairly fundamental particles pushing each other as described in the original question. I don't actually know what speed electricity travels at.

Another good idea, shadows. I would guess relativity would come in here to prevent the shadow moving faster than light, ie time rates would be different between the orbiting object and the observer of the shadow.

Anyway, I still think the "pole" idea has some legs.

Material made out of black-hole singularities? If you place two black-holes next to eachother they will become one black-hole. Similarly, I would assume a rod of black-hole singularities would become one singularity. Maybe you have references but I don't think a singularity bar would make any sense.

del88

Interesting idea.. one or two problems.
If the pole was made of neutrons as in a neutron star it would only be dense enough to have no space between the neutrons if it was 12km wide or over 1.35 solar masses....now if the pole extended like a tube (which it couldn't) and remained at 12km in diameter it would become a black hole when it got to 10 solar masses or around 90km long.....long way off Proxima Centauri.
Now let's say by some unknown law of nature we could force the neutrons right up tight against each other with no space between them and stretch them from here to Proxima Centauri ....hmmmmm the more i think about it the more i'm not too sure.....
Probably the pressure wave not being able to go faster than light would be the biggest stumbling block....maybe a compression of space time along the pole woulg stop it going faster than light.....maybe the same forces that stop light going faster than light would kick in..
What would happen if the pole was a ring that came back to earth???

mikhail

spottyelephant wrote: »

I've thought about faster than light before too - but i'm no scientist, so have no idea of the answer. But humour me for a second.

My understanding is that gravity attracts mass at a set speed. But on earth, things reach terminal velocity due to wind resistance. So, if you were in space where there was no resistance, you'd just keep accelerating. Is that right?

If so, what if you built a ship that had two extendable arms out in front of it (or something), and it could generate a gravitational pull in front of itself.

Presumably, the ship would just continually accelerate, because the the gravitational pull is always the same distance and same force, with no opposing resistance (like wind). So surely the ship would just keep going faster and faster, eventually beyond the speed of light.

As i said, im no scientist, but im pretty sure my theory is flawless!

No, it wouldn't. The arms exert exactly as much gravitational force on the rest of the ship as the rest of the ship exerts on the arms. The ship would experience no acceleration.

Now, if something massive is ahead of the ship and unconnected to it, there'll be acceleration, but only until they collide.

Corkscrewkenny

Morbert wrote: »

Material made out of black-hole singularities? If you place two black-holes next to eachother they will become one black-hole. Similarly, I would assume a rod of black-hole singularities would become one singularity. Maybe you have references but I don't think a singularity bar would make any sense.

Yeah, OK, fair point. I was just trying to give an example of the densest thing I could think of to get rid of the pressure wave problem.

Probably the pressure wave not being able to go faster than light would be the biggest stumbling block....maybe a compression of space time along the pole woulg stop it going faster than light.....maybe the same forces that stop light going faster than light would kick in..
What would happen if the pole was a ring that came back to earth???

The more I think about it, there are other factors like the effect the pole would have on the spacetime around it, and within it.

I thought about the pole comming back to earth too but I gave up trying to figure what the time effects of that would be (if the results of the push were felt back on earth instantaneously, at faster than the speed of light, then the results, I presume, would arrive before the pole was pushed in the first place, because the "information" would travel backwards in time)

But it is still counter intuitive to me that even a pole made of, say, aluminiom from here to Saturn would take over 1 hour and 14 minutes before the push was registered on Saturn.

What I really want is for Einstein to come back from the dead and post a comment to this thread along the lines of "Well done Corkscrew, I did'nt think of that".

Podge_irl

Corkscrewkenny wrote: »

But it is still counter intuitive to me that even a pole made of, say, aluminiom from here to Saturn would take over 1 hour and 14 minutes before the push was registered on Saturn.

Lots of physics is counter-intuitive. The very concept of a universal speed limit is counter-intuitive. That's why we run experiments and formulate theories in strict mathematics.

Zen65

Corkscrewkenny wrote: »

I don't actually know what speed electricity travels at.

The speed of travel of electricity is a lot slower than light speed.


Z

Capt'n Midnight

Zen65 wrote: »

The speed of travel of electricity is a lot slower than light speed.


Z

very roughly 1/10 c

Corkscrewkenny

Podge_irl wrote: »

Lots of physics is counter-intuitive. The very concept of a universal speed limit is counter-intuitive. That's why we run experiments and formulate theories in strict mathematics.

Thats the whole point. Think outside the box. No theories based on mathematics, theories based on logic.

ZorbaTehZ

Capt'n Midnight wrote: »

very roughly 1/10 c

Err... where did you get that figure from? You would need one hell of a current to get anything even close to that.

gentillabdulla

Corkscrewkenny wrote: »

Thats the whole point. Think outside the box. No theories based on mathematics, theories based on logic.

Actually its easier to know the physics first.

Then use logic.

After that just keep searching until you find anything that contradicts what you say.

Finally prove it with math.

Capt'n Midnight

ZorbaTehZ wrote: »

Err... where did you get that figure from? You would need one hell of a current to get anything even close to that.

can't remember, and yes it's not an average speed more like the soonest that an impulse into a wire comes out of the wire and that's ignoring capacitive and inductive effects

Corkscrewkenny

gentillabdulla wrote: »

Actually its easier to know the physics first.

Then use logic.

After that just keep searching until you find anything that contradicts what you say.

Finally prove it with math.

Thanks, a very helpful discription.

Anything more than quadratic equations and I haven't got a clue. I'm stuck with logic, simple thought experiments and physics programmes on TV.

There is one maths thing (and it's probobly stupidly simple): why do the digits in a number that is a multiple of 9 always add up to a multiple of 9, and does this hold for (say) the number 7 in an octal numeral system.

I've just thought about it and I think 7+7=86 (8+6=14)????

Rubecula

Corkscrewkenny wrote: »

Thanks, a very helpful discription.

Anything more than quadratic equations and I haven't got a clue. I'm stuck with logic, simple thought experiments and physics programmes on TV.

There is one maths thing (and it's probobly stupidly simple): why do the digits in a number that is a multiple of 9 always add up to a multiple of 9, and does this hold for (say) the number 7 in an octal numeral system.

I've just thought about it and I think 7+7=86 (8+6=14)????

This only occurs in the way you describe in the decimal system. Hexadecimal, Octo and Binary have their own rules. As would any other numerical system.

Corkscrewkenny

Rubecula wrote: »

This only occurs in the way you describe in the decimal system. Hexadecimal, Octo and Binary have their own rules. As would any other numerical system.

Yeah.

8+8=16 (1+6=7, one lessthan 8)
7+7=14 (1+4=5, two less than 7)
6+6=12 (1+2=3, three less than 6)

and etcetera. with ever more complicated rules for different combinations of numbers, cubes and so on.

Jack Black was wrong in School of Rock, 9 isn't a particularly "magic" number.

Morbert

Corkscrewkenny wrote: »

Thanks, a very helpful discription.

Anything more than quadratic equations and I haven't got a clue. I'm stuck with logic, simple thought experiments and physics programmes on TV.

There is one maths thing (and it's probobly stupidly simple): why do the digits in a number that is a multiple of 9 always add up to a multiple of 9, and does this hold for (say) the number 7 in an octal numeral system.

I've just thought about it and I think 7+7=86 (8+6=14)????

Yes, it would hold for the number 7 in a base 8 number system.

7+7 = 16 (1+6 = 7)
7+7+7 = 25 (2+5 = 7)
7+7+7+7= 34 (3+4 = 7)

Or the number 4 in a base 5 number system etc.

4+4 = 13 (1+3=4)
4+4+4 = 22 (2+2=4)

etc.

Corkscrewkenny

Morbert wrote: »

Yes, it would hold for the number 7 in a base 8 number system.

7+7 = 16 (1+6 = 7)
7+7+7 = 25 (2+5 = 7)
7+7+7+7= 34 (3+4 = 7)

Or the number 4 in a base 5 number system etc.

4+4 = 13 (1+3=4)
4+4+4 = 22 (2+2=4)

etc.

Gotcha

Podge_irl

Corkscrewkenny wrote: »

Thats the whole point. Think outside the box. No theories based on mathematics, theories based on logic.

Well my point is that no matter how counter-intuitive you find these things they're still right.

Our current theories aren't "based" on mathematics, they're based on experimental evidence - they're just formulated in mathematics as it's the natural language of physics

Corkscrewkenny

Podge_irl wrote: »

Our current theories aren't "based" on mathematics, they're based on experimental evidence - they're just formulated in mathematics as it's the natural language of physics

I agree, I understand, I comply.

I'll just make 1 point (maybe better described as a rant).

That an object reaches infinite mass if it moves through spacetime at the speed of light will never be proven with empirical evidence. It matters not that all theories and experimentation thus far point to this conclusion. Does mathemathical description not breakdown when it produces infinity as a result?. There can never be empirical proof. It can only ever be a theory.

Please just check the first capitalised word in the first post to this thread. I simply question if there is, in all theories of relativity and quantum mechanics and any other academic field one cares to use, any supposition(whether produced by theoretically or empirically) that points to the movement of information by this method, at faster than the speed of light, being impossible.

Podge_irl

Corkscrewkenny wrote: »

That an object reaches infinite mass if it moves through spacetime at the speed of light will never be proven with empirical evidence. It matters not that all theories and experimentation thus far point to this conclusion. Does mathemathical description not breakdown when it produces infinity as a result?. There can never be empirical proof. It can only ever be a theory.

The fact that the speed of light is a constant in any reference frame has however been proven empirically.

Talk of infinite mass is, in some ways, a poor way of describing relativity. You're right in that talk of infinities doesn't really make sense, but any massive body travelling at the speed of light doesn't make sense either. It's simply not possible for anything with mass to travel at c, so it's irrelevant what our theories imply happen at that point.

The primary point of special relativity is the equivalence of non-accelerating reference frames. That has been proven experimentally. The transfer of information at faster than the speed of light contravenes this experimentally proven idea. If information could travel faster than light than future events could affect the past, we would lost all sense of causality.


I really, really don't wish to seem condescending, but these discussions are best had through the medium of mathematics and proper theoretical physics, not abstract thought experiments.

gentillabdulla

Corkscrewkenny wrote: »

I agree, I understand, I comply.

I'll just make 1 point (maybe better described as a rant).

That an object reaches infinite mass if it moves through spacetime at the speed of light will never be proven with empirical evidence. It matters not that all theories and experimentation thus far point to this conclusion. Does mathemathical description not breakdown when it produces infinity as a result?. There can never be empirical proof. It can only ever be a theory.

Please just check the first capitalised word in the first post to this thread. I simply question if there is, in all theories of relativity and quantum mechanics and any other academic field one cares to use, any supposition(whether produced by theoretically or empirically) that points to the movement of information by this method, at faster than the speed of light, being impossible.

And I would like to mention that an object with mass that travels close to light speed never really gains mass.

It actually has an increase in inertial mass.As in it gets harder to accelerate.

Just a common misconception.

sponsoredwalk

Corkscrewkenny wrote: »

Does mathemathical description not breakdown when it produces infinity as a result?.

Look at this equation:



Forget about everything in it except for the stuff at the bottom of the fraction.

you see the √(1 - v²/c²) well the v² is your speed & the c² is light's speed.

You can never have v² = c² because if they are equal then v²/c² would equal 1!!!!!!!

If this happens then we will have √(1 - 1) = √0 & if we have zero underneath a fraction that makes complete nonsense in mathematics.

There are serious reasons why you shouldn't do this, as this quick video makes perfectly clear.

So, v² always has to be less than c²

This just gives you a sense of what it means for the mathematics to make sense,
if you think this is all wrong then you better get on the phone to the LHC people @ cern pretty quick

Corkscrewkenny

Podge_irl wrote: »

If information could travel faster than light than future events could affect the past, we would lost all sense of causality.


I really, really don't wish to seem condescending, but these discussions are best had through the medium of mathematics and proper theoretical physics, not abstract thought experiments.

No problem, with my physics education (TV) you can only but sound condecending.

I was about to reference this Rom Mallette guy (whom I learned about in a TV documentary) and his ideas about transmitting information to the past, but I read the "objections" section in his Wiki entry and they make more sense.

gentillabdulla wrote: »

And I would like to mention that an object with mass that travels close to light speed never really gains mass.

It actually has an increase in inertial mass.As in it gets harder to accelerate.

Just a common misconception.

OK, I also was told this on a TV program. What I think you're saying is that it gains kinetic energy as it accelerates (or is accellerated). Mass and energy are the same, with reference to the universal constant of light speed (E=Mc2). So matter travelling at light speed would require E>Mc2, or E+M.

sponsoredwalk wrote: »

This just gives you a sense of what it means for the mathematics to make sense,
if you think this is all wrong then you better get on the phone to the LHC people @ cern pretty quick

Thanks, I appreciate your time and effort. and I see your point in the equation. And I think the whole LHC project is a triumph of the human curiosity. I'll let them get on with it.

I think I read somewhere once of a theory that information/knowledge, once created, cannot be destroyed, so maybe the same laws apply to it as apply to matter and energy.

del88

gentillabdulla wrote: »

And I would like to mention that an object with mass that travels close to light speed never really gains mass.

It actually has an increase in inertial mass.As in it gets harder to accelerate.

Just a common misconception.

Quick question slightly off topic....
If an object gains inertial mass as it accelerates then would it be also true that all matter has been gaining inertial mass since the big bang ......and because the universe is still accelerating they are still gaining inertial mass....kinda like a ticking clock.

Capt'n Midnight

Corkscrewkenny wrote: »

I think I read somewhere once of a theory that information/knowledge, once created, cannot be destroyed, so maybe the same laws apply to it as apply to matter and energy.

Nope it don't refer to knowledge it only applies to physical information, not to "meaningful data"
http://en.wikipedia.org/wiki/Physical_information

Words in science can have specific meanings rather than the general meanings they have in everyday life. As a counter example the word OR to a computer programmer means they can pick both options.

some solutions suggest that even if the information isn't lost it's still unavailable
http://en.wikipedia.org/wiki/Black_hole_information_paradox#Main_approaches_to_the_solution_of_the_paradox

Podge_irl

del88 wrote: »

Quick question slightly off topic....
If an object gains inertial mass as it accelerates then would it be also true that all matter has been gaining inertial mass since the big bang ......and because the universe is still accelerating they are still gaining inertial mass....kinda like a ticking clock.

The acceleration of the universe and the acceleration of a massive body within the universe are fairly separate things. It's the difference between moving in space and space itself expanding.

Enkidu

Special Relativity is a strange subject in some ways. A lot of the confusion stems from the fact that we sort of combine our Newtonian intuition* with a few facts from Relativity. Of course we then get confused because this hybrid makes no internal sense. It is best to just forget everything and see the world the way Special Relativity describes it.

Basically in special relativity space and time are one object, spacetime. Now this is often something that is just said, but to see what it means you need a little bit of maths.

Let's say we will call distance in space dx and distance in time dt. Special relativity then says that the distance between two points in spacetime, ds, is:

ds^2 = (dt^2) - (dx^2)


Now, something I will not go into, Special Relativity says that 1 second is 300,000,000 meters in the temporal direction.
Now, for example, if you just sit where you are for one second then you have gone from:
t = 0, x = 0

to

t = 300,000,000 x = 0

So, dt = 300,000,000 and dx = 0. Putting this into the above formula gives:

ds = 300,000,000

So you have covered 300,000,000 meters in spacetime just by sitting on your chair.


Now let's say you went from here to the moon in two seconds. Then you would go from

t = 0, x = 0

to

t = 600,000,000, x = 363,104,000

Putting these numbers into the formula above we get:
ds = 477,656,241.64 meters

Now the surprising thing about this number is that it is not much different from the spacetime distance you cover when sitting on your chair. In fact, if you sat on your chair for two seconds you would cover a greater distance. So a counterintuitive fact:
You are closer, in spacetime to the moon two seconds from now than to your own chair two seconds from now.

Now try something faster than light, going to the moon in one second.
That gives:
dt = 300,000,000, dx = 363,104,000
If you put this into the formula you get an imaginary number. Now distances can only produce real numbers. An imaginary number basically means that there is no sensible notion of distance between you and that point in spacetime. It doesn't have a distance from you. (If you understand my meaning it has a distance of N/A, not a distance of 0.)

The formula above:
ds^2 = (dt^2) - (dx^2)
is called the metric. It basically tells you the distance between things. It tells you what geometry is like. For anything that would involve faster than light travel the rules of geometry produce an imaginary distance. Since you can only cover a real number distance, this means it is impossible to get.

By the laws of geometry this area of spacetime is cut off from you, it has no sensible geometric relationship with your position.

That is why you cannot travel faster than light. Not because you'll get infinitely heavy or anything, but because it's geometric nonsense.


*Of course our intuition is actually not even as advanced as Newtonian Mechanics, otherwise it wouldn't have taken Newton to come up with it.

gentillabdulla

I would like to mention the last part.

There are many reasons why you can't travel faster than light.

1. Is the mathematical nonsense(Courtesy of Sponsoredwalk)
2. Is the sheer amount of inertial mass you would gain.
3. Is the infinite energy you would need
And 4 is the geometroic nonsense you stated.

So there isn't just one.

del88

Enkidu wrote: »

Special Relativity is a strange subject in some ways. A lot of the confusion stems from the fact that we sort of combine our Newtonian intuition* with a few facts from Relativity. Of course we then get confused because this hybrid makes no internal sense. It is best to just forget everything and see the world the way Special Relativity describes it.

Basically in special relativity space and time are one object, spacetime. Now this is often something that is just said, but to see what it means you need a little bit of maths.

Let's say we will call distance in space dx and distance in time dt. Special relativity then says that the distance between two points in spacetime, ds, is:

ds^2 = (dt^2) - (dx^2)


Now, something I will not go into, Special Relativity says that 1 second is 300,000,000 meters in the temporal direction.
Now, for example, if you just sit where you are for one second then you have gone from:
t = 0, x = 0

to

t = 300,000,000 x = 0

So, dt = 300,000,000 and dx = 0. Putting this into the above formula gives:

ds = 300,000,000

So you have covered 300,000,000 meters in spacetime just by sitting on your chair.


Now let's say you went from here to the moon in two seconds. Then you would go from

t = 0, x = 0

to

t = 600,000,000, x = 363,104,000

Putting these numbers into the formula above we get:
ds = 477,656,241.64 meters

Now the surprising thing about this number is that it is not much different from the spacetime distance you cover when sitting on your chair. In fact, if you sat on your chair for two seconds you would cover a greater distance. So a counterintuitive fact:
You are closer, in spacetime to the moon two seconds from now than to your own chair two seconds from now.

Now try something faster than light, going to the moon in one second.
That gives:
dt = 300,000,000, dx = 363,104,000
If you put this into the formula you get an imaginary number. Now distances can only produce real numbers. An imaginary number basically means that there is no sensible notion of distance between you and that point in spacetime. It doesn't have a distance from you. (If you understand my meaning it has a distance of N/A, not a distance of 0.)

The formula above:
ds^2 = (dt^2) - (dx^2)
is called the metric. It basically tells you the distance between things. It tells you what geometry is like. For anything that would involve faster than light travel the rules of geometry produce an imaginary distance. Since you can only cover a real number distance, this means it is impossible to get.

By the laws of geometry this area of spacetime is cut off from you, it has no sensible geometric relationship with your position.

That is why you cannot travel faster than light. Not because you'll get infinitely heavy or anything, but because it's geometric nonsense.


*Of course our intuition is actually not even as advanced as Newtonian Mechanics, otherwise it wouldn't have taken Newton to come up with it.

very well explained.....cheers

The one thing that i always find tricky to understand is the measuring of speed when describing "traveling faster then light"....
If lets say I'm in space in a rocket and traveling away from the earth at 1000mph,then that speed can only be measured relative to the earth. Effectively me and the rocket are always stood still and everything else is either moving towards me or away from me at varying speeds.
Now if i hit the boost button then all I'm doing changing my speed relative to everything else...I'm not really moving....

Does anyone know what the greatest difference in speed between two objects in the universe is.......like the difference in speed between two stars on opposite sides of the universe...just curious

Enkidu

gentillabdulla wrote: »

I would like to mention the last part.

There are many reasons why you can't travel faster than light.

1. Is the mathematical nonsense(Courtesy of Sponsoredwalk)
2. Is the sheer amount of inertial mass you would gain.
3. Is the infinite energy you would need
And 4 is the geometroic nonsense you stated.

So there isn't just one.

It requires no energy to exist in a given reference frame, only move to move between reference frames. Also the only notion of mass that makes sense in relativity, invariant rest mass, does not change. Reason 1 is a consequence of reason 4. Geometry is the central reason, in fact it is central to relativity.

Enkidu

del88 wrote: »

Does anyone know what the greatest difference in speed between two objects in the universe is.......like the difference in speed between two stars on opposite sides of the universe...just curious

Less than the speed of light.

Capt'n Midnight

Enkidu wrote: »

It requires no energy to exist in a given reference frame, only move to move between reference frames. Also the only notion of mass that makes sense in relativity, invariant rest mass, does not change. Reason 1 is a consequence of reason 4. Geometry is the central reason, in fact it is central to relativity.

you need your E=mc2 energy to exist

anyone care to post up the total energy of a moving mass ?

Enkidu

Capt'n Midnight wrote: »

you need your E=mc2 energy to exist

anyone care to post up the total energy of a moving mass ?

True, but let's take that as a given. The point is that an object in an inertial frame moving close to the speed of light will, in another reference frame, it's rest frame, appear to be stopped. Hence there is no additional energy for moving fast.

The total energy of a moving mass will then be a frame dependent quantity.

Podge_irl

Capt'n Midnight wrote: »

anyone care to post up the total energy of a moving mass ?

E^2 = (pc)^ + 4(mc^2)^2?

Does anyone know what the greatest difference in speed between two objects in the universe is.......like the difference in speed between two stars on opposite sides of the universe...just curious

There are a number of issues to address here but the most important one is that there is a massive difference between movement in space and expansion of space. One of the main reasons for believing in the inflationary theory of expansion of the universe is precisely because the opposite ends of the universe that we can see - two points that can not have been in causal contact - have all the same physical properties. Two bodies can not move away from each other at more than the speed of light, but there is no such restriction on space itself expanding which is something that confuses a lot of people.

Corkscrewkenny

Podge_irl wrote: »

There are a number of issues to address here but the most important one is that there is a massive difference between movement in space and expansion of space.

I have a handle on the reason for supposing dark matter exists. But, as I understand it, what dark energy is doing is creating space at all points in the universe. We don't feel the effect of this because the gravity environment in which we exist cancels the effect of dark energy.

I'll postulate what dark energy is by putting 2 theories together.

Gravity is a weak force because most of it's energy is leaking into other dimensions (that exist as per string theory). This energy is being returned by expanding space (the conservation of energy).

Anonymo

Corkscrewkenny wrote: »

I have a handle on the reason for supposing dark matter exists. But, as I understand it, what dark energy is doing is creating space at all points in the universe. We don't feel the effect of this because the gravity environment in which we exist cancels the effect of dark energy.

I'll postulate what dark energy is by putting 2 theories together.

Gravity is a weak force because most of it's energy is leaking into other dimensions (that exist as per string theory). This energy is being returned by expanding space (the conservation of energy).

I'm afraid you're a bit muddled up here. If what you were saying were truly correct then in our 3+1 dimensions we'd recognise some lack of conservation of energy. What you're talking about is a particular aspect of string theory called brane dynamics. In this the standard model forces (strong, weak, electromagnetism) are confined to live on a 3+1 dimensional brane. Gravity can live in the bulk which is 9+1 (or 10+1 in M theory) dimensional. This certainly could explain why gravity is weaker since it is 'leaking' into the other dimensions. There is no reason to return this force to the brane. There is a possible explanation for the inflationary period after the big bang that goes along the lines of: get two branes, one an anti-brane and the other a brane. Put the anti-brane near the top of a throat (which has larger radius than where the brane is). The brane gets attracted to the anti-brane and it's the motion throught the throat where it expands that looks like inflation. That's more or less the general idea.

By the way you're initial idea of information transfer by moving a mass is flawed. There is no instantaneous information transfer to a separate body. The whole body (neutron star) feels the push but since the energy of the push is transferred to kinetic energy within the neutrons this is necessarily less than the speed of light. The transfer of 'information' of the movement of the neutron star to proxima centauri will also occur at less than or equal to the speed of light.

Corkscrewkenny

Anonymo wrote: »

I'm afraid you're a bit muddled up here. If what you were saying were truly correct then in our 3+1 dimensions we'd recognise some lack of conservation of energy. What you're talking about is a particular aspect of string theory called brane dynamics. In this the standard model forces (strong, weak, electromagnetism) are confined to live on a 3+1 dimensional brane. Gravity can live in the bulk which is 9+1 (or 10+1 in M theory) dimensional. This certainly could explain why gravity is weaker since it is 'leaking' into the other dimensions. There is no reason to return this force to the brane. There is a possible explanation for the inflationary period after the big bang that goes along the lines of: get two branes, one an anti-brane and the other a brane. Put the anti-brane near the top of a throat (which has larger radius than where the brane is). The brane gets attracted to the anti-brane and it's the motion throught the throat where it expands that looks like inflation. That's more or less the general idea.

By the way you're initial idea of information transfer by moving a mass is flawed. There is no instantaneous information transfer to a separate body. The whole body (neutron star) feels the push but since the energy of the push is transferred to kinetic energy within the neutrons this is necessarily less than the speed of light. The transfer of 'information' of the movement of the neutron star to proxima centauri will also occur at less than or equal to the speed of light.

Thanks dude (or dudetta).

On your first point, I'll have to read it a few times and then on to wiki again.

On your second point, one of the best explanations in the thread. I'm now firmly convinced information transfer by this method at faster than light cannot, even in theory, be done. On second thoughts, I'm not exactly firmly convinced. We don't know everything, particularly as relativity and quantum mechanics don't apparently reconcile (why was the LHC built). Maybe in the sub-atomic world kinetic energy transfer by this method would be a different story. On third thoughts your probobly right.

FISMA

Careful ladies and gentlemen, you're playing very loose with definitions that are very specific.

For example, watch out when stating the "total" energy in the equation

This equation is for a "particle," not a rod, spaceship, or such. Herein, the particle has no internal structure. It cannot rotate, for example, thus you will not see rotational kinetic energy here.

Extended objects have more than kinetic and rest energies which is from what the above is derived.

For example, an extended object will have internal energies: thermal, chemical, nuclear, and so on.

Concisely: you cannot plug the mass of the space shuttle and its speed relative to the Earth into the above equation and get the sum total of all Energies inherent in the space shuttle. Watch the terminology of "total."

Now, they'll do this in Introductory Physics books, however, a close read will demonstrate they are treating the space ship as a point particle.

Finally, there's the assumption that the Potential Energy of the particle is zero.

On the topic of electricity, most people think that electricity travels close to the speed of light. Physicists do not.

Any peice of wire that does not have a potential difference applied across it has electrons in random motion. Theses charge carries are going pretty fast, about 10^6 m/s. However, there's no net effect of current due to the random motions.

Even in my room, the gas molecules move with large speeds, about 500m/s due to their thermal energies. Then why are we not "hurricaned" away? Because the average velocity of these random motions is, essentially, zero. Just like the free electrons in the wire with no potential difference across its ends.

There may be a breeze in my room, caused by pressure differences at two windows. Likewise, the free electrons in the metal (roughly one per atom) can also have an overall drift, when there's a potential difference applied across the conductor.

This drift speed is on the order of fractions of a millimeter per second: 10^-4 m/s or 10^-5 m/s for the usual copper wires. If you would like to see the calculation, I would be more than happy to oblige.

So don't think that any thing, or anything, is actually traveling close to the speed of light in the wire, not even close. The effect, may be that lights turn on almost instantaneously when the switch is flipped. But, nothing is traveling even close to c.

Finally, there's a bit of confusion with the speed of light and upper limits.

Einstein was saying that no thing, nothing with mass, may ever be accelerated to the speed of light. No thing (with mass), can go the speed of light or faster.

A lot of people conclude that Einstein believed that there isn't anything, even the massless, that can go faster than the speed of light. As if everything in the universe (with or without mass) is bound by the speed of light.

Not true.

Einstein held out that there may be a superluminal "realm" (for the lack of a better word) where faster than c was possible.

Finally, Einstein did believe that such a realm may exist, however, we would lack the ability to perceive it, analyze it, understand it, et al.

One may wonder if, mass is just another form of Energy (E=mc^2 - mass - energy proportionality), to what was Einstein speculating in this superluminal world.