Thursday 21 October 2010

The cosmic speed limit always holds

There's a question I've come across that often sparks some debate, and I feel I'm in a position to give some clarification.

The question in hand pertains to the cosmic speed limit - that of light. As I'm sure most (if not all) of you know that no object can travel faster than light, which has an astounding speed of 300000000 metres per second. That's pretty fast.

It is also accepted that information cannot travel faster than light. Let's say a coin is tossed, and if it lands on heads a red light will immediately activate, or green for tails. Since information cannot travel faster than light, there is absolutely the no way an observer at any distance could know the result of the coin toss before the light emitted reached them.

The question is this -  Two people are at a great distance from each other, holding a long rod between them. If someone at one end pushes the rod, will the other person feel the push before any light could have traveled between the two?

At first, the answer seems to be yes. For instance, let's imagine the distance is a lightyear (the distance light will travel exactly 1 year). It appears illogical that it could possibly take the recipient one year to feel the push.

However, information CANNOT travel faster than light. When the rod is pushed, the entire object does not move at once. Instead, a pressure wave is formed at one end of the rod which travels through the entire object. Imagine a slinky. Holding it horizontally, should you push one end quickly while keeping the other end still, you would see a wave travel from one end to the other. This is what is happening in our rod. You don't seen this on an everyday level, for objects like pencils and rulers this takes place in under nanoseconds.

The wave in the rod will travel slower than the speed of light, and Physicists can sleep easy knowing that the laws of relativity remain intact.

21 comments:

  1. objects can (potentially) travel at the speed of light, meaning that it arrives before it is seen. we don't have a way of doing this obviously, but the speed of light isn't some universal "limit", and it's also not constant - the speed at which light "moves" depends on what it is travelling through.

    as for the "feeling the rod" thing, it's impossible even if the rod moved as a whole since the light would get there before the nerves in the hands could send the information to the brain, so it's busted either way

    ReplyDelete
  2. just found this blog ... I'll be back

    ReplyDelete
  3. Seb - admittedly, yes, I've glossed over a few things in this article. As far as light as a cosmic speed limit, it still holds for different materials - it is merely the speed limit through that medium.

    As for the nerve argument, should this thought experiment take place over a great distance, say on the magnitude of light years, then that time is negligible.

    Theoretically, it may be possible for other objects to travel at the speed of light, but for this to happen the object in question must have no mass.

    ReplyDelete
  4. Physics blows me away this late at night. My guess is that we may find out on a future episode of the Big Bang Theory.

    ReplyDelete
  5. this took me a good 10 mins to read and understand
    0.0

    ReplyDelete
  6. fullowin 'n' suppin :)

    wtfiniggagun

    ReplyDelete
  7. You got me thinking on a friday evening.. Damn you. ;)

    ReplyDelete
  8. i like that stuff too, becoming an engineer.
    especially the laws of thermodynamics, too.

    check my blog as well, you may be interested in some stuff, too.

    ReplyDelete
  9. The thing is, its still technically impossible to test most of these things. So we are just working in the realm of theories.

    ReplyDelete
  10. Einstein proved that for an object with mass to accelerate to the speed of light, their mass would become infinite.

    This is the reason that even if life exists out there, I dont think we will ever find it because its so far away.

    ReplyDelete
  11. Very interesting post, looking forward to reading more.

    ReplyDelete
  12. Good post to get thinking on too bad it's Friday will revisit this idea on Monday lol.

    ReplyDelete
  13. I wish we could travel at the speed of light

    ReplyDelete
  14. Wow very insightful, wish I could travel that fast!

    ReplyDelete
  15. great read, i love a good sciency read as i wake up

    ReplyDelete
  16. @teddypin no you don't wish you could travel that fast, because time would stop for you.

    +following this blog.

    ReplyDelete
  17. Very interesting. I really hope you post more!

    ReplyDelete