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Author Topic: Why are scientists so sure that the light barrier is impenetrable?  (Read 11232 times)

Offline latebind

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If history has taught me anything, it's this : Whenever human kind is faced with a barrier we eventually break through.

There are so many examples, including the sound barrier which no-one thought could be broken either.

As the kinetic energy and speed of an object increase, then so does its mass (E=mc2).
This suggests that to go the speed of light would require infinite energy...

This does not make sense when you think about the fact that the universe expanded faster than the speed of light at the beginning of the big bang, so its been done before.

Also , if you could have an accelerating spaceship orbiting the solar system with frequent fuel topups, then why would it not go faster than light? and why would its thrusters stop producing enough energy to propell it a little faster each minute?


To me, personally, this just looks like another barrier that human kind is going to eventually break one day. And I don't mean bypass with wormholes, I mean we will take an object past the speed of light one day...

BTW cool theory here :: http://www.space.com/businesstechnology/080813-tw-warp-speed.html

 


 

Offline graham.d

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In my opinion scientists are not "sure" of anything. To be sure would be a matter of faith, not science. We all use abbreviated language so it is more convenient to state something as a fact rather than preface every statement with, "according to our latest understanding (which may be wrong)...".

So, according to our current understanding on which much of our knowledge and understanding is based, nothing can travel faster than light. Maybe this is wrong, but it would certainly be a matter of faith to say so. It would be ignoring the knowledge we have. If we do not base our assertions on our scientific understanding, we could make any assertion we like without any need for evidence and could ignore contradiction with observations wherever we choose.

I don't remember seeing any theory invoking of faster than light expansion of the universe, but there may be one.

The faster than light spaceship idea is not a correct understanding of special relativity. The spaceship will get asymptotically closer to the speed of light but would never get there. To the people on the spaceship the universe would be contracting in the direction of motion. There would be (given a supply of fuel) no reason why they could not travel considerable distances (as measured by a stationary observer) in a reasonable timespan (to them). But this would not be what the stationary observer would see. He would see them limited to below lightspeed. Time dilation would make space travel rather problematic.

I would like to think we could find a way around this too but it is unscientific to just take this as a matter of faith because we would like it to be so.
 

Offline LeeE

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I think latebind is referring to the Inflationary Epoch phase of the Big Bang, where it's believed that the universe expanded faster than 'c'.  However, although the universe may have been expanding faster than 'c' this is not the same as saying that the objects (particles) that existed within the universe were moving through the universe faster than 'c', just in the same way that the receding galaxies are not moving through space but it is that the volume of space that they are within that is moving (due to expansion).

An analogy would be to think of people sitting inside an airliner whilst it's flying along at around ~600mph.  The people are stationary relative to the body of air inside the airliner but that body of air is traveling along at ~600 mph relative to the air outside, with the people inside the airliner moving along with it.
 

Offline graham.d

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You are probably right, Lee. Also, the universe model today is based on comoving observers where the comoving distances divided by the age of the universe would have objects moving faster than light. It is possible (and accepted) that the universe could be much larger than the observable universe but that these objects are "cosmically censored" from being observable. That this does not violate Relativity theory is not so easy to explain. It is really that it is the whole universe that is expanding and there is no reason why parts of this universe cannot be receding from us faster than c but that this has no impact on the laws of physics in either of our local frames of reference.
 

Offline doppler1

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One thing is for sure and that is that scientists can not be certain of very much. I know that one light year is a measure of distance travelling at the speed of light but how is that affected in a contracting universe? Could we say that if the destination point was 1000000 light years away when we left but is moving closer to the departure point thanks to the contraction of the universe....could we not say that we travelled faster than light, just for the hell of it, because we would have reached our destination in a shorter time than calculated...albeit in a pretty decrepit state and the distance has been reduced.....Just kidding....but really :)
 

Offline graham.d

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Actually Doppler you could do exactly that given a suitable supply of energy. You could travel considerble distances (as measured from the rest frame before you start) and the time you would take to get there (as measured by you) would be the classical time as if relativity had no effect. However, if you returned in similar fashion you would find the earth you left would be much aged with maybe your grandchildren older than you, for example. There is no reason why you would be decrepit.

This is a special relativity view. I'm not sure how this gets adjusted by, for example, a constant acceleration which would need to take into account a General Relativity view. I think the principle is the same but the maths may work out slightly differently.
 

Offline doppler1

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Sheesh, thanks a mil graham.d......as Neilep would say...ewe people are very smart on this forum. I will be sure to look into special relativity because this fascinates me. I am way out of my depth though but will try and find something I can understand in the theory. Thanks again.
 

Offline yor_on

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Doesn't the speed of light, and its covariance for all frames possible, define the theory of relativity? Wouldn't we have to build a new physics platform without that fact? That fact that light always will be measured at 'c' from whatever frame you measure it I mean, and whatever you measure it against too, moving or not. I think 'c' will stand for our universe. If we ever find a way to 'surpass it' it won't be through getting there faster. It will have to be something else, like 'tunneling' perhaps?
 

Offline Shadec

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ecause if you factor the speed of light into the equations:
1. for observed time:
tv= t0/√(1-(v2/c2))

2. for observed mass:
mv= m0/√(1-(v2/c2))

if you subbed v (the speed of the object) into the equation as c (ie it's traveling at the speed of light c, ~3x108) , you'll get 1/1 = 1, then you'll have √(1-1) = √0 (and that doesn't go down too well with physicists and mathematicians) but is generally accepted as being zero, so you would be dividing by zero, which is a big no-no. NEVER, EVER divide by zero!

so you get an undefined answer for both mass and time

Oh, and then there's length:

lv = l0 x √(1-(v2⁄c2))

which would end up as l0 x 0 = 0
length of zero, undefined mass and time...
not fun!

 

Offline Ron Hughes

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Since the required force to reach C (with respect to an observer) for any mass is infinite then M = ~/C^2. As you can see that is an awful lot of mass.
 

Offline krytie75

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Personaly I think the consideration of cross-universe travel by means of faster than light motion is fools errand.  Even if we subsequently (somehow) discovered that faster than light speed travel was possible, there's still the huge factor of time dilation, where any space traveller employing this method would arrive at their destination in the far future of earth or wherever they left from.  All we can hope for really is the discovery of some 'wormhole' technology that would allow us to cross vast distances in a negligable amount of time.
 

Offline Shadec

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There was something else I forgot to mention, if you went faster that the speed of light, for the same equations:

tv= t0/√(1-(v2/c2))
if you had say
tv= t0/√(1-((c+1)2/c2))
(which is only 1m/s faster than c, not very much faster!)
√1- (c2+2c +1)/c2
which I work out to be √-0.000000007
 Then you would end up as √-ve. And square rooting a -ve number is a massive no-no. Those are two of the most important rules, never divide by zero, and never square root a -ve number!! (unless you want to go into imaginary numbers and 'i', which still wont make you go at 3x108m/s)

And of course, the same goes for the other equations, as they all have √(1-x), with x being the speed division.

I would be inclined to agree with Krytie, there are far more useful things to be doing with our time than trying to travel faster than light. Though not necessarily spending it making wormholes!
« Last Edit: 15/04/2010 05:22:06 by Shadec »
 

Offline JP

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Then you would end up as √-ve. And square rooting a -ve number is a massive no-no. Those are two of the most important rules, never divide by zero, and never square root a -ve number!! (unless you want to go into imaginary numbers and 'i', which still wont make you go at 3x108m/s)

That brings up a good point (though one that's more science fiction than science).  It's theoretically possible to have imaginary-mass particles called tachyons.  Tachyons are always moving faster than the speed of light.  The more energy you put into them the slower they go (approaching the speed of light) and the more energy you take out the faster they go.  Of course, no one has seen them and there would be a lot of problems for causality if they suddenly showed up since you'd have time travel.
 

Offline yor_on

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So how about the quantum eraser experiment and the delayed choice quantum eraser. In where you have a possibility, according to some views, for the photons to 'communicate' pass the time barrier, our arrow of time that is. It seems to me as if you also could see this as some sort of 'ftl' if we by speed mean a measurement of distance in time :) After all they are not at the same place, are they, ah, inside our 'four dimensional' reality I mean. :)

The real question is if there is any 'information' exchanged of course, but if there are?
 

Offline Good Elf

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Hi All,

There have been some excellent comments made. You "can" travel "faster than the speed of light" as determined from your "rest frame" within a rocket as commented on previously by graham.d and yor_on and others learned people here. The problem is time dilation... On the one hand relativity "gives" by allowing a spaceship to travel any distance it want within any predetermined finite amount of time provided we have some way of protecting the travelers from radiation and acceleration and an also an unlimited source of propulsive energy. Unfortunately time dilation also means that the travelers are "projected" along a near null geodesic into the distant future as reckoned by an external observer from earth. This reconciles the fact that observers viewing this phenomenon from the rest frame of our galaxy or our solar system see this traveler moving near the speed of light (effectively indistinguishable from a beam of light). From this external observer point of view the travelers proper time is progressing very slowly to the point that it is almost "entirely arrested". At the same time it has "relatively" undergone nearly infinite length contraction which "appears" like a rotation of nearly 90 degrees away from the axis of travel placing the traveler and his spaceship very close to the lightcone wall as a "nearly flat object".

This can be put another way... time always "seems" to progress normally to the traveler as he views it from within his spaceship though peering outside he sees the complementary effect in the universe around him. the surrounding universe (which appears to him to be the object in motion) has compressed into the forward direction as a flat object and rotated almost 90 degrees on to the lightcone wall. The problem is "inertia". Acceleration produces dilation of local clocks relative to "homebound" clocks. The accelerated clocks "run slow" relative to unaccelerated clocks.

The "problem" seems hopeless since any hope of traveling faster than the actual velocity of light depends on moving through the exact velocity of light. That is a point at which all temporal processes as observed by external observers cease entirely and the spaceship and it's occupants move exactly like light. Forget the "mass" becoming infinite... there are "other interpretations"... see Lev B. Okun's papers on the matter (.. such as "Mass versus relativistic and rest masses" [nofollow] - 03 Dec 2008)... just one amongst many papers.

Unfortunately how is any object going to accelerate through that "node".... at the speed of light (as reckoned by any external observer) since it requires some temporal acceleration from within that frame... that will not occur? Energy exchange is required for acceleration and that is not about to happen from within that system in which time "appears arrested".

So another way must be found... you cannot move "through" the velocity of light but "around it" in some way. The way to do this is to do what Dr. Who does... invent a TARDIS (Time And Relative Dimension In Space)... Accelerate through space and time together maintaining some control over both. You can do this by "first" nulling the mass of the spaceship. This is what is holding the spaceship back and limiting the amount of acceleration (it also provides you with achievable sources of energy to accelerate your spaceship and also solves that difficult problem of "time dilation" which is "pushing" you rapidly into the future). The next thing is to accelerate in a controlled way ... and any force will cause an infinite acceleration on a zero mass but be sure to adjust the passage of time appropriately otherwise you will end up on the wall of the lightcone (as before) and be eternally "stuck" there. You can do this trick using certain quantum techniques which undoes the quantum exchanges occurring due to the natural passage of time.

Some additional reading material...
The Quantum Zeno Effect [nofollow]
Delayed Choice Quantum Eraser Experiment [nofollow]
A quantum solution to the arrow-of-time dilemma - Lorenzo Maccone 25 Aug 2009 [nofollow]
Uncollapsing the wavefunction - Andrew N. Jordan [nofollow]
Uncollapsing of a quantum state in a superconducting phase qubit - Nadav Katz etal [nofollow]
Exerting better control over matter waves [nofollow]

Next trick after reading and absorbing all this is you then need to research this thoroughly and build the TARDIS. Next point is to drop by and pick me up so we can both go for a "spin around the universe".  ;)


« Last Edit: 16/04/2010 12:59:28 by Good Elf »
 

Offline JP

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The "problem" seems hopeless since any hope of traveling faster than the actual velocity of light depends on moving through the exact velocity of light. That is a point at which all temporal processes as observed by external observers cease entirely and the spaceship and it's occupants move exactly like light. Forget the "mass" becoming infinite... there are "other interpretations"... see Lev B. Okun's papers on the matter (.. such as "Mass versus relativistic and rest masses" - 03 Dec 2008)... just one amongst many papers.

Unfortunately how is any object going to accelerate through that "node".... at the speed of light (as reckoned by any external observer) since it requires some temporal acceleration from within that frame... that will not occur? Energy exchange is required for acceleration and that is not about to happen from within that system in which time "appears arrested".

So another way must be found... you cannot move "through" the velocity of light but "around it" in some way. The way to do this is to do what Dr. Who does... invent a TARDIS (Time And Relative Dimension In Space)... Accelerate through space and time together maintaining some control over both. You can do this by "first" nulling the mass of the spaceship. This is what is holding the spaceship back and limiting the amount of acceleration (it also provides you with achievable sources of energy to accelerate your spaceship and also solves that difficult problem of "time dilation" which is "pushing" you rapidly into the future). The next thing is to accelerate in a controlled way ... and any force will cause an infinite acceleration on a zero mass but be sure to adjust the passage of time appropriately otherwise you will end up on the wall of the lightcone (as before) and be eternally "stuck" there. You can do this trick using certain quantum techniques which undoes the quantum exchanges occurring due to the natural passage of time.

Yeah invariant mass is the way to go when describing relativity phenomena.  But if you set your invariant mass to zero you have to instantly be going at the speed of light.  It's not a matter of accelerating to the speed of light.  Although it's probably a moot point unless there's a plausible physical process that lets you set your invariant mass to zero.
 

Offline JP

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So how about the quantum eraser experiment and the delayed choice quantum eraser. In where you have a possibility, according to some views, for the photons to 'communicate' pass the time barrier, our arrow of time that is. It seems to me as if you also could see this as some sort of 'ftl' if we by speed mean a measurement of distance in time :) After all they are not at the same place, are they, ah, inside our 'four dimensional' reality I mean. :)

The real question is if there is any 'information' exchanged of course, but if there are?

Yeah--there are plenty of ways for quantum "stuff" to move at FTL speeds.  But actually using any of that stuff as information always seems to require opening up a classical information channel which is limited by light speed...
 

Offline Good Elf

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Hi JP, yor_on and all,

That quote you made above "Quote from: yor_on on 15/04/2010 11:53:16" was from my post  ;D...
Quote from: JP
But if you set your invariant mass to zero you have to instantly be going at the speed of light.
Note... setting invariant mass to zero does not necessarily mean setting momentum to zero too... the exception is the photon.
Quote from: JP
Although it's probably a moot point unless there's a plausible physical process that lets you set your invariant mass to zero.
Um... I can think of one... of course it relies on what you mean by "physical". If you set a system into a superposition of states and the system wavefunction remains uncollapsed... the property of mass along with all other properties will remain "undefined" until it collapses as a unique classical "measurement". That measurement might be "forced" some distance away from the original systems location prior to being set into that quantum state.

Cheers
 

Offline JP

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Quote from: JP
Although it's probably a moot point unless there's a plausible physical process that lets you set your invariant mass to zero.
Um... I can think of one... of course it relies on what you mean by "physical". If you set a system into a superposition of states and the system wavefunction remains uncollapsed... the property of mass along with all other properties will remain "undefined" until it collapses as a unique classical "measurement". That measurement might be "forced" some distance away from the original systems location prior to being set into that quantum state.

Zero mass is perfectly well defined.  And even if it's in a superposition of states, each one evolves according to physical laws as if it's state was well-defined, so you shouldn't have zero mass, no matter what your definition of mass is.  This isn't the same as setting the invariant mass to zero so that you can go at the speed of light.
 

Offline Good Elf

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Hi JP,

Quote from: JP
Zero mass is perfectly well defined.  And even if it's in a superposition of states, each one evolves according to physical laws as if it's state was well-defined, so you shouldn't have zero mass, no matter what your definition of mass is.  This isn't the same as setting the invariant mass to zero so that you can go at the speed of light.
Regarding Quantum Electrodynamics... Just pointing out what is obvious... There are no "classical paths" to evolve along for quantum events so mass "falling" along a geodesic while in a quantum state is not able to be determined... only probability outcomes for events. If sufficient material has dephased completely into a "classical particle" it will be possible to track this particle along a path.... however it will no longer "diffract" as a quantum event. These probabilities may be calculated but the calculations cannot be used to choose a path along which an event might evolve... an example is the Double Slit Experiment (which also works for "slow moving" quantum matter particles) in which all "ways" must be summed in order to calculate these statistical outcomes.

Still this wave equation calculation (describing the wave-function) does not in any way constitute a "measurement". An actual measurement will define one state to be valid and all other states to be invalid. The "chance" of that single event happening out from all events possible is usually individually "insignificant". That is the difference between a measurement and this simple statistical calculation. The wave-function describes a global quantum state as probability while the measurement itself tells us the outcome of a "classical measurement" where the quantum particle has already become "dephased". This "measurement" entangles the measuring instrument with the event being measured. Statistics cannot be 'misused" to define paths. We also know that a formal measurements can only occur where there is a suitable measuring apparatus installed.

Nothing is "perfectly well defined" unless it is measured. While in a superposition of states (while a quantum) it cannot be measured. It may be possible to define a partial or protective measurement in the vein of Yakir Aharonov, though this will not usually provide definitive information about a specific event simply because that would collapse the state. It is a measurement problem and provided it is quantum mechanically isolated from the rest of the system will have no classical value... yet. A "full on" measurement will collapse that state. The next most important point is where you make that measurement since all "classical measurements" are local. That means that a particle might be able to tunnel across a barrier unlimited by classical considerations... this is not that "impossible" and the speed of that tunneling has no upper bound on velocity within the evanescent field.
« Last Edit: 20/04/2010 03:33:00 by Good Elf »
 

Offline JP

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I could argue with a lot of what you're saying here, but to keep things on point, you haven't addressed my post.  You claimed you could set your invariant mass to zero somehow, which would let you travel at the speed of light.  I said you can't do this.  How does your above post addresses this?
 

Offline Good Elf

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Hi JP,

Quote from: JP
You claimed you could set your invariant mass to zero somehow, which would let you travel at the speed of light.  I said you can't do this.  How does your above post addresses this?
No I didn't say anything about travel "at" the speed of light... I meant instantaneous connections through the well known phenomenon of quantum tunneling... that is a lot faster than light. I am not actually claiming anything other than there are well known principles you might like to apply to this general problem... read above.

If a particle is in a quantum superposition state you cannot determine any property and the particle remains unmeasured. It is literally an unknowable... not only for you (the observer) but also to the rest of the universe provided it is decoupled quantum mechanically. While in that state it is "protected" from observations.

This should be seen in the same vein as entangled down converted BBO photons... the properties of the individual photons are not determined until one of the pair "dephases" and is read as an observation. Before this event... it is experimentally known that the states are not defined. At that point of dephasing no matter how far the entangled particles are apart there is an instantaneous connection that determines their orthogonal properties. This this has been experimentally determined and is entrenched in the Bell Inequality [nofollow]. There is an even stronger relationship if the particles are both within the evanescent field... such as in wave mechanical (quantum) tunneling [nofollow]. Until the classical property of mass is "collapsed" out in a measurement, it's final position and value will be determined through a measurement/observation when it dephases from the wave state and quantum entangles with the detector transferring it's qubit. The position of the detector determines where the particle has "traveled" to but it does not determine any specific path. Just apply Quantum Electrodynamic Principles to the particle and you then understand what I mean.
 

Offline JP

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Hi JP,

Quote from: JP
You claimed you could set your invariant mass to zero somehow, which would let you travel at the speed of light.  I said you can't do this.  How does your above post addresses this?
No I didn't say anything about travel "at" the speed of light... I meant instantaneous connections through the well known phenomenon of quantum tunneling... that is a lot faster than light. I am not actually claiming anything other than there are well known principles you might like to apply to this general problem... read above.

This is what you said:
Quote from: Good Elf
You can do this by "first" nulling  the mass of the spaceship. This is what is holding the spaceship back and limiting the amount of acceleration (it also provides you with achievable sources of energy to accelerate your spaceship and also solves that difficult problem of "time dilation" which is "pushing" you rapidly into the future). The next thing is to accelerate in a controlled way ... and any force will cause an infinite acceleration on a zero mass but be sure to adjust the passage of time appropriately otherwise you will end up on the wall of the lightcone (as before) and be eternally "stuck" there. You can do this trick using certain quantum techniques which undoes the quantum exchanges occurring due to the natural passage of time.
My concern is with setting the mass to zero, which isn't achievable. 

Quote
If a particle is in a quantum superposition state you cannot determine any property and the particle remains unmeasured. It is literally an unknowable... not only for you (the observer) but also to the rest of the universe provided it is decoupled quantum mechanically. While in that state it is "protected" from observations.
That isn't true.  You can know plenty about the particle.  The thing you don't know is determined by how the system is set up.  If you entangle electrons with respect to spin, you can know properties other than their spin.  You know their masses, their charges, you can know their position and momentum (up to the uncertainty principle) and their energy. 
 

Offline Good Elf

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Hi JP,

Quote from: JP
Quote from: Good Elf
If a particle is in a quantum superposition state you cannot determine any property and the particle remains unmeasured. It is literally an unknowable... not only for you (the observer) but also to the rest of the universe provided it is decoupled quantum mechanically. While in that state it is "protected" from observations.
That isn't true.  You can know plenty about the particle.  The thing you don't know is determined by how the system is set up.  If you entangle electrons with respect to spin, you can know properties other than their spin.  You know their masses, their charges, you can know their position and momentum (up to the uncertainty principle) and their energy.
I am not sure if you are quite "getting this"... Properties such as spin, charge, optical polarization and mass are classical measurements. You can't know any of those things without collapsing the quantum state. You can entangle electrons ... etc... but you cannot know anything about these isolated quantum states until you actually measure them. Obviously it is very important to properly isolate the states and that may be hard... no denying that.

Before you actually measure the properties of these quantum states they do not have these properties... the properties actually come from the measurement and are interrelated. Check out the experimental details of Alain Aspect's Bell Inequality and also Yoon-Ho Kim, R. Yu, S.P. Kulik, Y.H. Shih, and Marlan O. Scully's Delayed Choice Quantum Eraser Experiment which is based on John Wheeler's original concept. The properties are determined at the time of reading of one of the entangled states. Setting up a "classical system" tells you nothing of the quantum state or where it is "evolving" to. After you measure the system it has become "classical" and the original quantum state has been "screwed up".

We obviously have a difference of opinion but I think I have said all I am prepared to say at this point... nice talking to you JP

Cheers
 

Offline diverjohn

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Another thought about exceeding the speed of light: if it were possible, how would we worry about the acceleration to and from such velocities?
 

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