# If I move a long solid stick can I send message fastest than light? [duplicate]

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Is it possible for information to be transmitted faster than light?

I mean by using a perfect solid stick long enough and moving it forward and backward can I send information fastest than light ? Can you imagine a solid stick long enough to reach the moon and using it to comunicate with the lunar base. Will be information faster than light? What are the theoretical reason other than technical reason for rules this as impossible? We should rule that a perfect unelastic solid exist ?

## migrated from theoreticalphysics.stackexchange.comFeb 17 '12 at 11:58

• This question should be on physics, not theoretical.physics : It's a classical popular science question. – Frédéric Grosshans Feb 17 '12 at 11:33
• Short answer: No, because the particles of the pole would need to move with more than speed of light. – Martin Ueding Feb 17 '12 at 12:14
• @queueoverflo No: the particle would not need to move faster than light. But compression waves would, which is equally impossible. – Frédéric Grosshans Feb 17 '12 at 13:45
• If you really accomplish creating a perfectly rigid stick, you would not be able to accelerate it. – Anixx Dec 17 '16 at 13:18

You give the answer yourself : special relativity forbids any perfectly rigid solid, or more quantitatively, give a bound on the elasticity a solid can have ($Y<\rho c^2$). If you have a real solid, with nonzero elasticity, you can compute the speed of sound within this solid as a function of the elasticity/stiffness (see e.g. on wikipedia for the formula). If you move an end of your big stick faster thant this speed of sound, it will compress the stick, and this deformation will take time to propagate to the other end. This question is one of the many non-working way of making faster than light communications. You have many of them debunked here.
No. Whenever you move a pole, this is what's actually happening: You push one end. The molecules at theis end push the next molecules. These molecules push the next, and so on. It really is a sort of sound wave, with an incredibly small frequency. There is a time lag between molecules pushing each other, which is again very small. If the rod is very long, these time differences will become apparent. So, someone one light-minute away will recieve the message in $14.4$ min, assimung an iron rod ( I got the ratio by dividing the speed of sound in iron by the vacuum speed of light)? The moon is $1.282$ light seconds away, so the rod will send the message in $18$ s. Pretty slow compared to what we have for moon communication (i.e, radio waves &c)