speed of light hypothetical

[axeman]

I know very little about relativity, but i have a situation that conflicts with what i've read on the internet. If you were sitting on a planet one light year away from earth and busted out your portable radio and tuned into an earth broadcast, you would be hearing the broadcast as it was one year ago. Now if you hopped in your spaceship and blasted back to earth at nearly the speed of light so that the journey would take one year and a day while listening to your radio, how would the broadcast play? I don't think it would play twice as fast because light measures the same speed no matter how fast you're moving. My theory is that the radio would play at normal speed, while on earth the year and a day would seem like only one day, meaning once you arrive home you would have heard the years worth of air time, plus the day's worth of broadcast emitted from earth since you left. But doesn't time go slower for you if you travel near the speed of light? Where does relativity fit into this?

[cperkinson]

You wouldnt be hearing broadcasts from one year ago... Radio waves travel at a slower rate than light.

[mooeypoo]

You wouldnt be hearing broadcasts from one year ago... Radio waves travel at a slower rate than light.

Actually, no it doesn't. Radio waves *ARE* electromagnetic waves, which *ARE* light waves, only with different frequency.

 

Light waves and radio waves are both the same speed, they just have different frequency, which means they might travel through different obstacles.

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Now as for the OP question ,that's a good one. I'll have to think about it. Technically, light moves the same speed in all frames of reference, but radio waves have "information" within them (different frequencies represent infromation, for example, in FM waves). I believe (I need to check this) that there will be a quite large effect of "stretching" the wave - doppler effect. However, I will need to think about this a bit further to give a definitive answer.

 

I'm hoping one of the other Physics experts helps me out here, too, before I get back to you on that one

 

~moo

Edited June 17, 2009 by mooeypoo
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[cperkinson]

I am most definately going to have to disagree. NOTHING travels as fast as light.

[cameron marical]

I think that It would come out jumbled since you are going against the direction of the waves near their speed. I dont think that It would come out faster because your right, the c is c, but I think that once they move the electrons in the antenna to the device etc... it would come out in jumbled and sound like nonsense, though I may be wrong. I am not really sure.

 

I think that relativity would just make the ride for you faster vs earths time, and the brodcasts you would zoom by, hence the jumbled radio. getting to earth you would be younger than say... if you had a twin {twins paradox}.

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I am most definately going to have to disagree. NOTHING travels as fast as light.

 

Radio waves are the same thing as light mate. their electromagnetic waves, just at different frequencys, so we register them differently or not at all. Their really the same thing in different versions.

Edited June 17, 2009 by cameron marical
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[mooeypoo]

I am most definately going to have to disagree. NOTHING travels as fast as light.

You shall have to review your physics, then, and disagree in your existing threads in the Pseudoscience/Speculations forum.

 

Nothing *WITH MASS* travels as fast as the speed of light, cperkinson.

 

Visible light is an electromagnetic wave with a certain frequency. Increase that frequency, and you get radio waves. Increase the frequency further, and you get all kinds of radiation. All of these are travelling at the speed of light.

 

See these:

http://en.wikipedia.org/wiki/Radio_waves

http://en.wikipedia.org/wiki/Electromagnetic_radiation

http://en.wikipedia.org/wiki/Electromagnetic_spectrum

 

And, please, if you have further questions about this, please continue this in your thread in P&S, seeing as this is starting to move away from conventional physics, which is what the Physics/Relativity threads are supposed to stick to.

 

At the very least open a new thread asking about the speed of electromagnetic waves, so we can continue this thread on topic and in accordance to the rules of the forum.

 

~moo

[cperkinson]

HMM while they may initially travel at the same speed, i dont believe radiowaves carrying information would travel the same speed as light. The information encoded within the waves would slow them down. RIGHT? And henseforth i would like to further state that in accordance to the origonal post that if radiowaves dont travel at the speed of light then the reworking of the question of how the radiowaves will sound will have to be rethunkified

[ajb]

The opening question is really "what happens to the frequency of EM radiation as measured by an observer moving relative to the source? "

 

See relativistic Doppler effect.

[axeman]

if you are having trouble with the fact that they're radio waves, try picturing it as viewing a car moving at a constant speed on earth instead.

 

I agree that it may be the doppler effect allowing the broadcast to play twice it's normal speed without the waves exceeding the speed of light. I might have to know how radio waves carry information to fully understand this question.

[swansont]

The observer pops into his Gamma100 spaceship which travels at .995c (so gamma=100). The trip takes him 3.65 days by his own clock, and a 366.8 days by the earth observer's clock. From ajb's link, the frequency shift is about a factor of 20 — he has to change his radio electronics. If the transmission was at 100 MHz, now he has to listen at ~2 GHz.

 

And he will get the entire (earth) year's worth of transmissions in that time. Nothing will have traveled faster than c.

[axeman]

I see, thanks.

[cperkinson]

1+2=3=2+1=3=1+2 say it however you want, it all still means the same thing

[ajb]

1+2=3=2+1=3=1+2 say it however you want, it all still means the same thing

 

I don't see your point or understand the attitude.

 

The opening question has been answered viz the relativistic Doppler effect.

[cperkinson]

The questions asked on this site are all related. And the answers are all similar in that they deal with physics in some way shape or form. And physics laws are based upon infinancy. "For every action there is an equal and opposite reaction."

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And if someone would like to argue the fact that not all questions are physics related. That is true. Not all questions are directly related, but are indeed related in some shape or form.

[mooeypoo]

You really need to stop expecting us to guess teh relationship of the logic you're using, cperkinson, and start showing us that relationship.

 

That said, I am INFORMING YOU, cperkinson, that your insistance that you're right is wrong, and that the subject you're leading this thread into is off-topic. I am thereby telling you to open your own thread about whatever you want to argue about the wrong speed of light of the wrong waves, and not hijack this thread, as it is against the rules.

Please go over our rules.

 

Let's return back on topic on this question, please.

 

~moo

[swansont]

HMM while they may initially travel at the same speed, i dont believe radiowaves carrying information would travel the same speed as light. The information encoded within the waves would slow them down. RIGHT?

 

Wrong.

 

How would you differentiate between EM radiation that carried information and one that didn't, anyway? I can send you a photon that represents a "1" in a digital transmission, and I can send you an identical photon that doesn't. Why would the "1" photon travel slower?

[SH3RL0CK]

For that matter, the presence (or absence) of the photon itself could be the information. When I send the photon, it cannot know whether I am just sending it and not expecting someone to see it, or if there is an observer waiting for it as his signal to go do something.

[Jacques]

mooeypoo:

Visible light is an electromagnetic wave with a certain frequency. Increase that frequency, and you get radio waves.

Radio waves have lower frequency than light

Electromagnetic spectrum

 

Also I want to add to Swanson reply that not only the Gamma100 passenger will need to tune is radio to 20 time the earth radio station frequency, but the information will comein 20 time faster.

 

But he will experience Relatisvistic time dilatation that may cancel the Doppler blue shift (or add the Doppler blue shift I am not sure...)

Edited June 17, 2009 by Jacques

[Janus]

mooeypoo:

 

Radio waves have lower frequency than light

Electromagnetic spectrum

 

Also I want to add to Swanson reply that not only the Gamma100 passenger will need to tune is radio to 20 time the earth radio station frequency, but the information will comein 20 time faster.

 

But he will experience Relatisvistic time dilatation that may cancel the Doppler blue shift (or add the Doppler blue shift I am not sure...)

 

The link ajb gave was for relativistic Doppler shift, which already takes Relativity into account.

[Jacques]

Thanks I didn't saw abj link

I copied the equation:

[math]f_o = \frac{1}{t_o} = \gamma (1-v/c) f_s = \sqrt{\frac{1-v/c}{1+v/c}}\,f_s[/math]

The wiki tell

( v is negative if the observers are moving toward each other).

If it is correct when v is .995c then [math]f_o=\sqrt{\frac{1+.995}{1-.995}}\,f_s=20f_s[/math]

OK:doh:

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Swansont

The observer pops into his Gamma100 spaceship which travels at .995c (so gamma=100).

I thinks there is an error: At .995 c I found gamma=10.

[proton]

HMM while they may initially travel at the same speed, i dont believe radiowaves carrying information would travel the same speed as light. The information encoded within the waves would slow them down. RIGHT? And henseforth i would like to further state that in accordance to the origonal post that if radiowaves dont travel at the speed of light then the reworking of the question of how the radiowaves will sound will have to be rethunkified

 

It's clear from this response that cperkinson doesn't understand what light is.

 

cperkinson - Light is an electromagnetic wave. A radio wave is also an electromagentic wave. The only difference between light and a radio wave is the frequency. This is not something that is disputed in physics. This is accepted as a well known fact and has been born out in the laboratory. This was proved by James Clerk Maxwell a very long time ago. To this point Maxwell wrote

The velocity of transverse undulations in our hypothetical medium, calculated from electromagnetic experiments of MM Kohlrausch and Weber, agrees so exactly with the velocity of light calculated from the optical experiments of Fizeau, that we can scarcely avoid the inference that light consists in the transverse undulations of the same medium which is the source of electric and magentic phenomena.

Why would you think otherwise?

Edited June 19, 2009 by proton

[cameron marical]

Ok, cperkinson. Im guessing that your around 12-17, still in high school and arent going to let anyone bring you down. I like that, I myself am 15, and am obesssed with science and engineering to the fullest. Wont let anyone tell me I cant, like you.

 

But, arguing with these people isnt the smartest thing to do, I did it in my first post and, of course, I lost, because I was wrong. Most {not all} of the people that post to questions know what they are talking about, and if they dont, someone who does know will call them on it, so your going to get true info if you listen to what these people say.

 

Dont just say that they are wrong and you are right, ask why they say your wrong. Dont just dissagree, tell them why you disagree. Word things better, instead of saying "no thats not right, say "but I thought...". It will help you out alot here, Ive learned so much stuff here, its amazing, and the stuff I didnt learn here, I learn from wikepedia links that people post here {or at school, but really, I learn more here than at school}.

i dont believe radiowaves carrying information would travel the same speed as light. The information encoded within the waves would slow them down. RIGHT?

 

Information "encoded" with things like radio waves etc... are just modulations in the frequencys and amplitudes { am and fm}, there is no mass associated with radio waves at all, So they all go the same speed {C, 186 miles per second}[roughly]

 

heres a link to a pic about that shows how it works

http://en.wikipedia.org/wiki/File:Amfm3-en-de.gif

Edited June 19, 2009 by cameron marical

[proton]

Information "encoded" with things like radio waves etc... are just modulations in the frequencys and amplitudes { am and fm}, there is no mass associated with radio waves at all, So they all go the same speed {C, 186 miles per second}[roughly]

You must be referring to rest mass. However, since light has energy it also has mass according to E = mc². Note that in this context the m in this expression is not rest mass. E is therefore not rest energy but total energy. For a photon all its energy is kinetic energy so that the mass of the photon is all from its kinetic energy.

 

Note: Some people refer to this m = E/c² as relativistic mass. Other people refer to it as inertial mass.

 

If you disagree with what someone is saying you really should provide a reason for it and not just disagree. Merely disagreeing is of no use to anyone except to convey the fact that you disagree. A solid arguement contains reasons. For example; cperkinson should have explained what he thinks light is, how it is different in nature to an electromagnetic waves, where he got such an idea, and any proof of it that he may know of.

[swansont]

Swansont

I thinks there is an error: At .995 c I found gamma=10.

 

Yes indeed. (Squaring/rooting mis-key, or I looked at the wrong calculation) v = 0.99995c

 

However, algebra aside, the concept is the important thing here. Nothing had to exceed c for this scenario to happen.

[cameron marical]

Proton;

 

Yes, I supporse I was reffering rest mass. It seemed to me that cperkinson was under the impression that a foreign particle was associated radio waves in order for their to be information.

 

I was under the impression that electromagnetic waves are usually refered to as massless. Was I wrong?

 

If you disagree with what someone is saying you really should provide a reason for it and not just disagree. Merely disagreeing is of no use to anyone except to convey the fact that you disagree. A solid arguement contains reasons.

 

Is this directed towards me?