# Faster than the speed of light [closed]

(I am not the origin poster of this question but I have failed to provide the references)

A scientist claims that he found the way to break the speed of light barrier - faster than the speed of light, with the following experiment:

He puts an object in the space that is exactly one light year away from the spot he's standing on earth. The object, without gravitational force or other influences, stay still.

Then he made a wooden stick that is almost one light year long, that is, the one end of the stick is in the scientist's hand while the other end is 0.1 mm away from the object. Assuming he can hold the stick (He might be Dr. Bruce Banner transformed)

With the above 2 completed, he now emit a light beam to the object, which in theory, takes 1 year to reach the object. At the same time, he moves forward his hand, poking the object in space through the stick in hand.

Question is: Is he actually faster than light, and why / why not?

• I don't understand how this is a puzzle. There are no tricks to it. The light will arrive at the object before the stick pokes it. Shouldn't this be in the physics exchange? – DiscOH Apr 29 '15 at 23:16
• @DiscOH The puzzle is to explain it, but yes, this is a physics problem. (that's why it's tagged physics :D) – user88 Apr 30 '15 at 0:36
• Although this is an interesting thought experiment, it is more appropriate for physics.se In fact, it has been asked five times on that site. One Two Three to be continued. – Len Apr 30 '15 at 2:41
• I'm voting to close this question as off-topic because it belongs on physics.se. However, there are already duplicates on that site. – Len Apr 30 '15 at 2:48
• off topic and still upvoted :P – user2408578 Apr 30 '15 at 8:03

No. When you push the stick forward you're actually sending a wave down the stick (think like flicking a long rope). This will be slower than light.

• A slightly better analogy, instead of the rope, would be to perhaps envision a spring that is pushed slightly at one end, sending a compression wave down the length of it, as this would more closely simulate pushing a stick. – Cubicon Apr 29 '15 at 21:23
• Great, that's the perfect analogy I needed but couldn't find in my head :-) Thank you! – DaveBensonPhillips Apr 29 '15 at 21:24
• Yep, and that travels at the speed of sound – BitNinja Apr 29 '15 at 23:38
• @BitNinja at the speed of sound in wood, which will be a great deal faster than the 340m/s in air – DaveBensonPhillips Apr 30 '15 at 6:43
• So does this mean the speed of light determines the limit of how rigid a material can be? – Juan Apr 30 '15 at 7:07

No he is not faster than the speed of light. Force has a speed of propagation and it will propagate through the stick at the speed of propagation. It will take either the same amount of time or longer for the force produced by him to reach the end of the stick to poke the box compared to the traveling light

No. The stick will break. :)

But seriously, as said above, the compression will travel at around the speed of sound in wood, which, at around 103 m/s, is around a hundred thousand times slower than the speed of light, around 108 m/s.

EDIT: Though it would be interesting to figure out how much force can be applied without the stick breaking and by extension, the actual amount of time required to touch the object

a) In the quickest way possible (the stick breaks during acceleration)

b) So the stick does not break during initial acceleration (but does after contact)

and c) So the stick won't break at all.

It will require OP post more detailed properties of the chosen cellulose-based laterally-elongated structure though :)

And what about the influence of gravitation?

I say:

no because the stick only traveled 0.1mm , regardless of when the light gets there.

You could do the same experiment with two persons on earth, X distance between them.

Place the stick (it will be shorter now) the same way between the two. Have the 2nd person be a foot and not 0.1mm from the end of the stick. Now when you press a button (or have Bruce Banner poke with the stick) have a humongous boom box blare a sound signal at the same time. Person 2 will get poked and AFTERWARDS here the blaring sound. That doesn't make the stick faster than sound. Its not the stick that made the sound, nor is the stick the one that made the light in the question.

• This actually make much more sense than the answer above. – Guillaume Apr 29 '15 at 23:05
• While it is the case that in the proposed situation, no physical object travels faster than the speed of light, there is still a signal transmitted faster than light, violating relativity. The other answer correctly recognizes that the signal would not propagate faster than light, whereas this one gives a misleading impression of what would physically happen. – user2357112 supports Monica Apr 29 '15 at 23:30
• That's OK, a one l.y. long stick also violates reality. – Mazura Apr 30 '15 at 2:58
• it would make more sense to use a flashing light than a boom box. In which case person 2, always sees the light first – Ewan Apr 30 '15 at 8:15
• @Mazura We (as a species) aren't currently able to make such a stick, but it doesn't violate any fundamental laws of physics. – user253751 Apr 30 '15 at 8:28

Alpha3031's initial assertion is more likely to be the correct answer. The weight/mass of the wooden stick (assuming about 10x10 cm square, by 1 ly long) would be around 5*1016kg. (the wider the stick the more mass, hence more force needed) The amount of force needed to move such mass will probably break it somewhere near the point when the force is applied. Some clever physics scientist will probably be able to estimate the distance of the breaking point ... :)