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ET phone home or anywhere really

  1. Jul 20, 2011 #1
    I know that for the longest time we have been listening to radio waves for some sign of life. I also recently heard that SETI was shut down do to lack of funds recently :cry:. I was just wondering, if there is another intelligent space faring race out there that was capable of extra-solar travel wouldn't they use something other than radio waves to communicate? Aren't radio waves "too slow" for that kind of reliable communication? After all, it takes several min for radio waves to go from here to the moon, so I could imagine what a pain it would be to talk to people that we send to the nearest star. Are there any theories as to how to communicate in more real time over such distances? Thanks.
     
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  3. Jul 20, 2011 #2

    Ryan_m_b

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    Radiowaves travel at the speed of light, since this is the fastest speed possible there is no other option for communication. We can't speculate on whether tool-using life elsewhere in the universe would or would not use radiowaves, all we can do is come up with different methods that we think could be used for communication and look for them. As we don't have an unlimited budget we favour looking for those that make more sense to us because they would be more efficient to use (such as the http://en.wikipedia.org/wiki/Hydrogen_line" [Broken])

    EDIT: forgot to mention it takes light ~1 second to get to the moon http://en.wikipedia.org/wiki/File:Speed_of_light_from_Earth_to_Moon.gif
     
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  4. Jul 20, 2011 #3
    Yeah, meant to say Mars not the moon. :wink:

    Other thought... I thought nothing could travel at the speed of light. But radio waves do? :surprised
     
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  5. Jul 20, 2011 #4
    Nothing with rest mass can travel at the speed of light. Radio waves are photons, which are massless particles; they just have a certain wavelength. Xrays, microwaves, gamma rays and radio waves are all photons with longer wavelengths.
     
  6. Jul 20, 2011 #5
    OK. Yeah, I remember reading that photons had no mass. Hmm... if photons have no mass then how do solar sails work? Wouldn't there need to be something physical pushing on them to make them move? My understanding was that light was "collected" by the sails and that pushed the sail away from the light source. If light has no mass how does it exert enough force on the sail to make it move?
     
  7. Jul 20, 2011 #6
    Even though photons don't have mass, they do carry momentum (p = E/c), and they tranfer this momentum to the solar sail vehicle.
     
  8. Jul 20, 2011 #7
    How do they transfer that momentum if there is no mass to cause friction?
     
  9. Jul 20, 2011 #8

    Ryan_m_b

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    Anything massless travels at the speed of light, radio waves are photons with a frequency measured in megahertz but are still photons. Altering the frequency of a photon will alter what part of the http://upload.wikimedia.org/wikipedia/commons/c/cf/EM_Spectrum_Properties_edit.svg" [Broken] it belongs to.

    I believe that http://en.wikipedia.org/wiki/Newton's_laws_of_motion#Newton.27s_third_law". I'm not an expert but what I think happens is the photons are absorbed then re-emitted by the atoms in the sail, this results in momentum being thrown one way resulting in momentum in the opposite direction.
     
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  10. Jul 20, 2011 #9
    Hmm... those photons are odd little things. So if what everyone has said is correct, then a solar sail could be potentially driven/powered by light, radio waves, Xrays, microwaves, and gamma rays since they are all photons.?

    Actually, let me just try and clarify something... every time I have heard the term photon it was referring to light. But you guys are saying that radio waves, Xrays, microwaves, and gamma rays are also photons. So... is it better to say a photon is just a particle/wave with no mass?
     
  11. Jul 20, 2011 #10

    Ryan_m_b

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    Light can either mean the electromagnetic spectrum or visible light. So you could say that
    radio waves are light, we just can't see them with our eyes.
     
  12. Jul 20, 2011 #11

    Drakkith

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    Yep!

    A photon is the "particle" of all forms of Electromagnetic Radiation. Electromagnetic radiation is everything from radio waves all the way up to gamma rays. See here: http://en.wikipedia.org/wiki/Photon

    It is better to say that a photon is massless but has momentum. And yes, it has BOTH wave like and particle like properties, and so does all matter!
     
  13. Jul 21, 2011 #12

    Ryan_m_b

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    I just remembered something, even if we did have a means to communicate faster than light we would then run into http://en.wikipedia.org/wiki/Tachyonic_antitelephone" [Broken]. Essentially any FTL reply you get to a FTL message will arrive before you sent the original message.
     
    Last edited by a moderator: May 5, 2017
  14. Jul 21, 2011 #13
    Wouldn't that only apply if you sent it to yourself? If you are sending such a signal to a point that is far away from you (let's just say a light year) then this would just mean that the message would arrive faster than if you sent a radio signal... right?
     
    Last edited by a moderator: May 5, 2017
  15. Jul 22, 2011 #14
    No this is not the case. FTL communication causes causality violations because it contravenes SR. To move/communicate FTL would cause violations in SR as from some valid frames of reference this would be seen to be moving "backwards" in time, these FoR are also valid and so this is a causality violation as an event cannot be seen to have happended before it has actually happened, regardless of the FoR. While still new to SR i believe this a consequence of SR Lorentzian transformations.

    There are some good articles online with regards to FTL communication violations. :) Happy reading.
     
  16. Jul 22, 2011 #15
    That I never knew......but what causes the photon to appear in different forms ie radio waves gamma waves etc. Does it repsond to certain electro magnetic stimuli?

    Thanks
     
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