I think there is no limit to highest achievable speed as claimed by Einstein. I have a thought that its because of our limit that we can't comprehend objects traveling faster than light(as we see objects using our eyes which uses light and there is limit to speed of light), we are bent to believe that nothing can travel faster than light. Although it doesn't affect the reality at all because all we see is all what matters. But the truth remains the same as I see no clear reason to why would such a great universe would put a limit on it's highest speed and why would it choose it as speed of light. I wish to know your view on this and make me aware if there's something I am missing or if you have a reason to disagree.

In order to clearly show what I am trying to say I have made the following example. Consider, a capsule starting from \( x = 0\) at \( t = 0\) and moving with speed \(k \times c\), where \( c \) is speed of light and \( k > 1\). Consider an observer sitting at \( x = 0 \) calculating the speed of capsule. After \(1\) second the capsule would have reached \(x =k \times c\). The capsule is visible to observer at all times. But consider that the observer calculated its speed noticing the light it just emitted at that instant that is at \(t = 1 \). The observer would see that light not at that instant because it would require time for light to reach that observer and that time would be equal to \( k + 1 \). Finally, the observer would conclude the speed of capsule to be \(\frac {k} {k+1} \times c\) that is always less than speed of light. But indeed he is terribly wrong as we all know. Similarly, aren't we mistaken for years believing there is limit to highest achievable speed.

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## Comments

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TopNewestTo go faster, you need more energy. The amount of energy in the universe is limited, so there must a maximum achievable speed.

I'm not proficient enough in physics to make deep statements, but according to Einstein we'd need an infinite amount of energy to reach the speed of light, which is impossible. To go faster, we'd need more than that, which is even more impossible.

I followed some physics classes when still a student, but no book ever explained properly why Einsteins formulas make sense. Why is the cap at the speed of light? It always seemed arbitrary to me, though it's a fact that there is SOME limit to speed.

I'm not trying to say that Einstein is wrong, but I'm asking why is he right?

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Undoubtedly, Einstein's theory regarding relativity have helped making so many advances. It doesn't make any difference in saying that objects can faster than light because we would still see the world with our eyes and in fact all his formulas would apply thereby.

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Not entirely true. If we could travel faster than the speed of light, we could visit other solar systems within a reasonable amount of time. It's then irrelevant what we observe.

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If a ship was travelling faster than the speed of light, a photon emitted from a flashlight inside the ship parallel to its direction of motion would be traveling faster than the speed of light, even if you say that time runs infinitely slower on the ship from the perspective of the outside, the photon will still be moving at a velocity greater than c. To remedy this you would have to evoke negative lengths and negative time, which is much more ridiculous than a universal speed limit.

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Since people asked about tests of the speed of light...yes there are lots of experiments that have been done to test special relativity and the speed of light. For example, this is a standard reference in the field of testing relativity and has a list of many experiments, although some sections are admittedly advanced. As far as I know there is no comprehensive list built for students just getting started in physics. Suffice it to say, the limits on the speed of light being the maximum achievable speed are very, very tight.

It is not true, however, that one immediately runs into causal paradoxes like the grandfather paradox when trying to build theories with faster than light signals. Those theories can be built and are well behaved. They just tend to be wrong experimentally, although there are some exceptions.

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@EDIT in OP; The observer would know that the light takes time to reach him and correct his calculation accordingly, giving him the right speed of \(k*c\).

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Yes, you are right.

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Hmm, you got me there!

Problem arising is that the observer wouldn't be able to see the capsule at all. If it's moving faster than light, there would be no light hitting the capsule on it's back to return to the eyes of the observer...

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This is what I believe. The main problem we are facing whether to define science as comprehended by our senses

(which is done),or "simply what actually happens there". I just doubt thatjustfaster than light velocity can warp time and space, and thus the ban highest possible velocity. This simply doesn't make sense. According to me, there should be other factors, which present day science cannot comprehend, which are ignored when the velocity increases i.e. comparable to the speed of light. There's gotta be some sort of explanation for the experimental results, confirming the theory of relativity as proposed by Einstein.Log in to reply

Is it ever been proven by anyone that light speed remains constant regardless of the reference frame?

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Read up on the Michelson-Morley experiment.

Also, I highly recommend watching episodes 41-44 of The Mechanical Universe, which deal with special relativity and its development.

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Might be like this: as we are travelling at 99.999%

cand when we want to walk forward, it will be like you are trying to walk through the metal (solid) according to relativity.Log in to reply

Consider a case, you are travelling in a hypothetical capsule at the speed of light. Now, if you walk inside the capsule in the direction of motion, you will travel at a speed faster than light... I too think why would Universe put a lim function to highest velocity. But it is an eternal accepted truth that light has equal speed irrespective of any refrence frame. Consider that case again, if you will be walking, you will be travelling back to time!

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I agree with you but this eternal truth might just be an illusion. As Einstein said something like this in one of his books that if you see some bowls; all as it is except one with blue strip emitting steam doesn't really mean that stream is because of that blue strip.

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Einstein's infinite mass equation might say that no mass can travel faster than light. This is proved in cern experiments. but don't worry... if it is so, then our universe can be seen expanding!

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suppose you are travelling at 99.999999999999999999999999999999% the speed of light. then we have to put an infinite force to just walk front!!! how will it happen??? according to me, light has mass(look at my massive photon theory). and the thing is that at that speeds, we will feel an illusion or glitching at those speeds and finally when we walk forward, we would feel that we are travelling towards the past!!!

Also, when we look around, we are actually seeing the 'nearest' past(statically and even when in motion).

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even cern has made protons reach 299,792,450 metres per second! we need to make it reach c

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Einstein has never said that the speed of light was the limit. He just states that nothing with mass can go faster than the speed of light. All mass less particles go as fast as the speed of light.Theoretically, objects with negative mass (anti matter) would be capable of traveling faster than the speed of light.

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Einstein's own theory of relativity talks about deciding a reference frame. If we are talking about speed limit to 'c' we are talking from a reference frame which is at very very less speed than 'c'. So actually if two reference frames are at a speed greater than 'c' Einsteins equations might still hold. Though energy required is very high.

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according to Einstein's theory,

cis the speed at which spacetime differences will bezeroLog in to reply

Einstein's Special Theory of Relativity states that:

The laws of physics are the same in all inertial frames. (1)

Among these physical laws are Maxwell's Equations, which show that the speed of light in a vacuum is constant.

The question is:

What frame is this speed relative to?

Historically, physicists answered this question with: "ether frame". However, the Michelson-Morley experiment was unable to show the existence of the ether.

Einstein reasoned that if Maxwell's Equations are the same in all inertial frames, then the speed at which light travels through vacuum must be the same for all inertial frames.

From (1), Einstein was able to show the following:

(2) The speed of light in a vacuum is the highest achievable speed. (3) An infinite amount of energy is necessary to accelerate a mass to the speed of light in vacuum. (4) Mass-Energy Equivalence (5) Lorentz Transformations

Consult a good physics book for mathematical details. As far as I know, it is unknown whether Einstein was aware of the results of the Michelson-Morley experiment when he (Einstein) was working on the Special Theory of Relativity.

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