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# Is lightspeed really a limit?

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### #1 sirchz

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Posted 10 October 2012 - 10:07 AM

Relativity and the speed of light is always a popular topic.

This was published in Proceedings of the Royal Society. The lack of any experimentally verifiable predictions is a problem. That aside, I wonder what would motivate the assumption that the product of velocities is limited to c^2? Maybe they just used something that would result in a "nice" mathematical solution?

“Einstein started working from information where the relative velocity is zero – what we knew about, such as rest mass, kinetic energy and so on – and then extrapolated what is known in the Newtonian world for velocities lower than c.

“Our thinking was: how do we make use of the essential essence of Einstein’s theory for velocities above c?”

Mathematically, what the mathematicians assumed is that for infinite relative velocity, there is a fixed relationship between the velocities of the two observers: where u is the first observer’s velocity, v is the second, the product of the two velocities is always c2.

“What we have is an equivalent theory [to Special Relativity] that applies for velocities beyond the speed of light. That theory is different from Special Relativity, but it has many of the same characteristics.

And readers with an interest in either physics or maths will be delighted with the vital assumptions: there has to be one, and only one, speed of light; and in all cases, a mathematical singularity occurs at the speed of light.

“If you believe what we’ve done,” Professor Hill said, “there can only be one speed of light in a universe. If there was a second speed of light, our mathematics wouldn’t work.

To get from the theory to any practical test is another matter entirely, and Professor Hill freely admits he doesn’t know how that might be achieved.

http://www.theregist...ty_mathematics/

### #2 deSitter

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Posted 10 October 2012 - 10:20 AM

Things are allowed to go faster than C, but only faster. Likewise less than C, but only less. Finally at C, and only at C. Thus, things going faster than C cannot interact with things going less than C, because one might cause the other to change its classification (e.g. annihilation into radiation). This is why tachyons are tacky.

-drl

### #3 Qwickdraw

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Posted 10 October 2012 - 11:29 AM

I have always had a suspicion that C is directly related to the expansion rate of the universe and could be slowly changing. Just a suspicion though.

### #4 Napersky

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Posted 10 October 2012 - 01:57 PM

In Space C is the speed limit. Outside of Space who knows?

### #5 scopethis

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Posted 13 October 2012 - 03:12 PM

traveling faster than light one becomes "infinite mass", somewhat akin to a ghost(??). what would one "see"?

### #6 Mister T

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Posted 13 October 2012 - 07:45 PM

if you look ahead you see everything.
if you look behind you see nothing

### #7 deSitter

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Posted 14 October 2012 - 08:20 AM

traveling faster than light one becomes "infinite mass", somewhat akin to a ghost(??). what would one "see"?

Here's what happens at high speed. Three interconnected phenomena occur:

1) Crowding of things into the direction of motion. Things that were behind now appear to be in front. If say you were headed directly toward the Moon, the Moon would appear smaller from crowding. Likewise if you were headed directly away from it, it would appear larger. Near C this becomes extreme, and the entire universe appears to be crowded into a small cone about the direction of motion.

2) Blue shifting of light from the forward direction, and red shifting of that from the rear. Near C this becomes extreme and things behind disappear, their light having shifted all the way into the far infrared. Things ahead gradually become bluer and bluer until they disappear into the far ultraviolet.

3) Intensification of radiation from the forward direction, and attenuation of that from behind. Near C this becomes extreme and the entire universe devolves into an intensely bright pinpoint of light, like a tremendously bright star, in the direction of motion. Everything else appears inky black.

Here's a video

-drl

### #8 Kon Dealer

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Posted 18 October 2012 - 05:21 PM

Einstein showed in his paper on Special Relativity the relationship between relativistic (M)and rest mass (Mo).

M is Mo divided by the square root of 1 minus (velocity squared divided by speed of light squared).

When V=C then you have Mo divided by zero, which is infinite. i.e. M becomes infinite, as does the energy needed to accelerate it.

Essentially as you accelerate a mass towards the speed of light an increasing amount of the energy used is converted into mass,according to Einstein's energy mass equivalence equation (E = M*C squared).

So nothing with rest mass can reach the speed of light. Only massless particles such as photons (light)

Try plotting the relationship between M and V on Excel- it is quite instructive

### #9 DarkSkys

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Posted 18 October 2012 - 09:00 PM

Einstein showed in his paper on Special Relativity the relationship between relativistic (M)and rest mass (Mo).

M is Mo divided by the square root of 1 minus (velocity squared divided by speed of light squared).

When V=C then you have Mo divided by zero, which is infinite. i.e. M becomes infinite, as does the energy needed to accelerate it.

Essentially as you accelerate a mass towards the speed of light an increasing amount of the energy used is converted into mass,according to Einstein's energy mass equivalence equation (E = M*C squared).

So nothing with rest mass can reach the speed of light. Only massless particles such as photons (light)

Try plotting the relationship between M and V on Excel- it is quite instructive

I'm probably not being original, But at what point would it be impossible to accelerate an object any more in reality( not on paper)

When you reach the point that even matter/antimatter power isnt enough?

### #10 Mister T

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Posted 19 October 2012 - 06:28 AM

the only way to answer that Q is to try it and measure the results.

so we HAVE to rely on the "on paper" answer.

the LHC does 99.99(?)% of c with a tremendous amount of energy/mass

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Posted 19 October 2012 - 06:39 AM

I'm probably not being original, But at what point would it be impossible to accelerate an object any more in reality( not on paper)

Never. You can keep accellerating and getting closer to C.

In practical terms, from the point of view of a stationary observer, there isn't much point as you get past 90% or so. From the point of view of earth, a probe launched a 0.9C toward a star 100 light years away will arrive in 111 years, one moving at 0.99C will get there in 101 years, and one moving at 0.99999C will get there in just over 100 years (not much difference between 101 and 100).

But from the point of view of someone riding the probe, it's a huge difference. Most of the additional energy put in to accelleration ends up increasing your time dilation. On the ship, a 100 light year trip at 0.9C takes 48.5 years. At 0.99C it takes 14.25 years, and at 0.99999C it takes just over 5 months.

Costs a LOT of energy, though. With the best current technology, we'd be lucky to achieve 0.01C.

### #12 Pess

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Posted 19 October 2012 - 09:40 AM

traveling faster than light one becomes "infinite mass", somewhat akin to a ghost(??). what would one "see"?

Actually, something that approaches 'c' approaches infinite mass. The point of 'c' is never reached..only approached. Infinite mass is never reached...only approached.

That is why 'c' is an effective speed limit. It can't be reached by any object possessing mass even if the entire mass of the Universe (except the object) were converted to energy in an effort to accelerate the object.

Ways around 'c'?

1) Take the object outside of normal space and accelerate it in a universe with different physical constants. Then just drop it back into our universe at sub-c. I'll leave the details to you guys.

2) Figure out what it is about particles possessing mass that determines their spatial coordinates in the fabric of space-time. Quantum theory tells us that an electron has a percentage chance to be found on either side of a barrier around a nucleus. What is seldom said is that there is also a certain probability that that same electron can be found on the other side of the universe. This 'probability' of finding it there is vanishingly small but still very real. Build a star ship that can manipulate this quantum probability and you can 'pop-up' anywhere in the Universe you want. I leave the details to you guys,

3) Build a Higgs-Bosun shield generator. When robbed of mass any particle instantly travels at 'c'. I'll leave the details to you guys.

4) If my back-of-the-envelope Lorenz transformation math is correct, if we can get a ship up to 99.9% speed of light the crew would experience 1 year for every 22.36 years Earth side observers would experience. Still, the size of the Universe dwarfs this so that explorers--even though removed from Earth kin due to time dilation--would still only find a tiny fraction of star systems reachable in their own lifetimes. Still, just need to adapt a Hemi V8 to a space craft and we are good to go. I'll leave the details to you guys.

Pesse (Get to work, you guys.) Mist

### #13 moynihan

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Posted 19 October 2012 - 09:47 AM

Matter cannot accelerate to meet or exceed the speed of light.
Matter can travel faster than the speed of light.
But perhaps most importantly, space itself may not be subject to the same limits.

A practical example?

Alcubierre Drive

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Posted 19 October 2012 - 12:34 PM

2) Figure out what it is about particles possessing mass that determines their spatial coordinates in the fabric of space-time. Quantum theory tells us that an electron has a percentage chance to be found on either side of a barrier around a nucleus. What is seldom said is that there is also a certain probability that that same electron can be found on the other side of the universe. This 'probability' of finding it there is vanishingly small but still very real. Build a star ship that can manipulate this quantum probability and you can 'pop-up' anywhere in the Universe you want. I leave the details to you guys,

Ah, yes, the old Improbability Drive. Excellent choice.

4) If my back-of-the-envelope Lorenz transformation math is correct, if we can get a ship up to 99.9% speed of light the crew would experience 1 year for every 22.36 years Earth side observers would experience. Still, the size of the Universe dwarfs this so that explorers--even though removed from Earth kin due to time dilation--would still only find a tiny fraction of star systems reachable in their own lifetimes.

Why settle for 99.9% C? That's only good for local travel. The discerning intergalactic tourist will take nothing less than 99.9999999999999% C. If you want to keep your inter-galactic cruise time under 1 year, that's the only way to travel.

### #15 Andy Taylor

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Posted 19 October 2012 - 12:53 PM

>>>Ah, yes, the old Improbability Drive. Excellent choice.

Yup, and you would be in time for dinner at the Restaurant at the End of the Universe...

### #16 Pess

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Posted 19 October 2012 - 01:50 PM

Why settle for 99.9% C? That's only good for local travel. {quote] The discerning intergalactic tourist will take nothing less than 99.9999999999999% C. If you want to keep your inter-galactic cruise time under 1 year, that's the only way to travel.

Pesse (I always obey all posted speed limits.) Mist

### #17 snowboycosmos

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Posted 16 November 2012 - 07:08 PM

In 1999 observations by the Hubble Space Telescope, the motion of M 87's jet was measured at four to six times the speed of light.

### #18 Carl Coker

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Posted 16 November 2012 - 08:15 PM

In 1999 observations by the Hubble Space Telescope, the motion of M 87's jet was measured at four to six times the speed of light.

True, but that's only an apparent speed caused by an optical illusion. If you correct for the light travel time and the fact that the jet is oriented towards us, the actual velocity you recover is lower than c.

### #19 StupendousMan

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Posted 16 November 2012 - 09:11 PM

I spend one day in my relativity class talking about these superluminal motions; maybe you'd enjoy the material.

http://spiff.rit.edu...m/superlum.html

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Posted 16 November 2012 - 11:27 PM

That's a pretty stupendous lecture. No fooling.

### #21 InterStellarGuy

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Posted 20 November 2012 - 11:47 PM

I'm probably not being original, But at what point would it be impossible to accelerate an object any more in reality( not on paper)

Never. You can keep accellerating and getting closer to C.

In practical terms, from the point of view of a stationary observer, there isn't much point as you get past 90% or so. From the point of view of earth, a probe launched a 0.9C toward a star 100 light years away will arrive in 111 years, one moving at 0.99C will get there in 101 years, and one moving at 0.99999C will get there in just over 100 years (not much difference between 101 and 100).

But from the point of view of someone riding the probe, it's a huge difference. Most of the additional energy put in to accelleration ends up increasing your time dilation. On the ship, a 100 light year trip at 0.9C takes 48.5 years. At 0.99C it takes 14.25 years, and at 0.99999C it takes just over 5 months.

Costs a LOT of energy, though. With the best current technology, we'd be lucky to achieve 0.01C.

The Orion pulse drive theoretically could achieve .1C, which just relies on nuclear bombs, and if powered instead by pulses from antimatter/matter reactions, theoretically .5 - .8 C.

### #22 Pess

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Posted 21 November 2012 - 02:06 PM

The Orion pulse drive theoretically could achieve .1C, which just relies on nuclear bombs, and if powered instead by pulses from antimatter/matter reactions, theoretically .5 - .8 C.

If 'c' becomes an effective barrier to speed then colonization ships are our only fallback position. And, as a practical outcome, these ships would become permanent habitats by the time any planet fall is made. Which, incidentally, might be an explanation as to the lack of neighbors dropping in to borrow a cup of sugar.

We don't really understand 'gravity' well enough yet to say 'c' is an absolute limit..at least in my mind. No mass will ever be accelerated by raw energy to 'c' velocity...but there may be undetected loopholes. For example, theory says no mass can be accelerated exactly to 'c'. Doesn't say anything about objects traveling above 'c'.

Pesse (Just got to get around the Universes speed trap.) Mist

### #23 llanitedave

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Posted 21 November 2012 - 11:42 PM

We don't yet have to say c is an absolute limit, since the practical limit occurs a lot earlier.

One of these days we'll face the fact -- speed is expensive, time is cheap. Live longer, go slower, enjoy the trip.

### #24 Mister T

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Posted 22 November 2012 - 10:06 AM

where's the profit in THAT!?

### #25 llanitedave

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Posted 22 November 2012 - 02:53 PM

The interest compounds as you go.

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