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# phone use at speed of light

Afaceinthematrix
Theoretically, if you were traveling in a space ship at or near the speed of light going away from planet Earth, and you were somehow able to make a phone call to someone on earth, how would that work? Since you're getting farther away from Earth (c*time), would the amount of time that you've spent traveling be equal to the amount of time that it takes the signal to reach earth (assuming the waves from the phone travel at the speed of light)? Also, if someone was observing this, so time dilation was occurring, and you talked to that person on the phone, how would that work out? I've been spending a lot of time thinking about this lately and I thought I would ask people who know more about science than me...
jsarnold
This is easy.

Assuming that your speceship is travelling at L x the speed of light, and Earth is moving at J miles per hour in a direction which is D degrees in relation to your ship, and that the destination phone is at position X, Y, Z on the surface, then the cost of making the call would be exactly twice the amount of money in the universe, and so you would be unable to make a connection.
Hogwarts
Wow. You're good at this :O

On a more serious note, this'd be impossible unless you were somehow able to make something go above the speed of light or somehow alter time.

Both of which, if even possible, would be really, really hard to do.
Bikerman
Simple answer is you can't travel at c. If you could then time would stop for you (a photon does not 'experience' time).
More detailed answer is that as the ship moves towards c the local time on the ship (as measured from earth) is slower and slower.
rockstar
A slight variation on this.......And as there seem to be a few bright sparks here......

Travel at the speed of sound, whilst once in the teritory of science fiction, has been a reality for quite a few decades now.

If two people are travelling in the same aircraft which is moving faster than the speed of sound, how come they can still speak to each other, without the sound being left somewhere behind?
jsarnold
For the same reason that all the passengers inside the aircraft are not blown up against the back wall and pinned there by the roaring gust of wind. The air inside the aircraft is moving at the same speed, and so the sound waves behave as normal.
rockstar
Ah, I see. So I guess thats the reason its pressurised.

Cheers
jsarnold
Actually no, it's not the reason. The air at 35,000 feet is at such a low pressure that humans would suffocate. The air inside is kept at as close a pressure as normal to allow for normal breathing. The shell of the airplane is therefore built to withstand the enormous pressure difference between the inside and the outside.

Even if the air inside was the same as the pressure outside, sound would travel normally, and you would still not be thrown against the back wall.
rockstar
Ah. I see. Thank you.
Afaceinthematrix
 Bikerman wrote: Simple answer is you can't travel at c. If you could then time would stop for you (a photon does not 'experience' time). More detailed answer is that as the ship moves towards c the local time on the ship (as measured from earth) is slower and slower.

Well I know that. That's why I said theoretically. But to at least make it possible, let's say that your traveling in a space ship heading away from Earth at 2.98x10^8 m/s... so very close to the speed of light... Would it basically just start taking an extremely long time for the waves from the phone to reach Earth? I'm not sure what the speed that they travel is at... this isn't my best area, which is why I'm asking...
jsarnold
Well first of all, radio waves generated from a mobile phone are much the same as light, simply oscillating at a different frequency - therefore the difference between the speed of light and the speed of radiowaves is a theortetical one.

But - on a more interesting note, a scientist appears to have managed to force mobile phone radiowaves to travel faster than the speed of light. Eistein's theory said that no information or particles can travel faster than light, but radiowaves are another thing entirely. This scientist has not only made radiowaves travel faster than the speed of light, but has demonstrated the equivalent of a sonic boom. All very interesting.

Therefore, if you are travelling away from Earth at just under the speed of light, and it was possible to send the mobile phone radio waves at just over the speed of light, then the signal would eventually get through, but obviously the sheer distance would cause a delay preventing real time conversation.

Here's a link to the full story if you're interested:

Afaceinthematrix
^^ Nice, thanks for the link. That was interesting. I'll have to look more into that. It seems like it can turn into a useful technology.
SonLight
 rockstar wrote: A slight variation on this.......And as there seem to be a few bright sparks here...... Travel at the speed of sound, whilst once in the teritory of science fiction, has been a reality for quite a few decades now. If two people are travelling in the same aircraft which is moving faster than the speed of sound, how come they can still speak to each other, without the sound being left somewhere behind?

Ignoring the other answers you received, which are insufficiently obscure IMHO, let me remind you that whereas the Michelson-Morley experiment tried to find an "ether" -- a hypothetical substance in which electromagnetic waves vibrated -- and failed to find it, there is an analog (analogue if you're British) of ether for sound waves. Sound waves vibrate the air and move with the air. Light waves vibrate independently of any medium, and as a result time itself varies for different observers, making the situation evan more difficult to understand intuitively than this obfusticated post.
bigt
 Afaceinthematrix wrote: Theoretically, if you were traveling in a space ship at or near the speed of light going away from planet Earth, and you were somehow able to make a phone call to someone on earth, how would that work? Since you're getting farther away from Earth (c*time), would the amount of time that you've spent traveling be equal to the amount of time that it takes the signal to reach earth (assuming the waves from the phone travel at the speed of light)? Also, if someone was observing this, so time dilation was occurring, and you talked to that person on the phone, how would that work out? I've been spending a lot of time thinking about this lately and I thought I would ask people who know more about science than me...

You'd have to use a sub-space transmission.. lol. or else you're going to be saying "can you hear me now?"

But seriously, I think this probably would be great to have; especially since we'd be able to travel at or near light speed.
Parkour_Jarrod
i believe that all phone calls are at the speed of light how else would you explain the possibility of me being able to talk to someone on the phone 5000KM away and the time it taking me to say something and them to hear it being a split second, that is faster than the speed of sound because going on the rule of sound it should take.... 2.7 hours (approx) for the speach to get their.
Indi
 Afaceinthematrix wrote: Well I know that. That's why I said theoretically. But to at least make it possible, let's say that your traveling in a space ship heading away from Earth at 2.98x10^8 m/s... so very close to the speed of light... Would it basically just start taking an extremely long time for the waves from the phone to reach Earth? I'm not sure what the speed that they travel is at... this isn't my best area, which is why I'm asking...

The signal would travel at c from the ship to Earth, no matter which way the ship was heading. So to figure how long it will take the signal to reach Earth, all you need to do is divide the distance by the speed of light.

But the signal would be distorted by relativistic effects - it would sound very, very slow. To calculate how distorted, you need the relative speed difference between Earth and the ship.

 jsarnold wrote: Here's a link to the full story if you're interested: http://www.santafenewmexican.com/HealthandScience/LANL_scientist_makes_radio_waves_travel_faster_than_light

Is this a joke? Seriously, this is the stupidest science article i have read in months (that wasn't on the Onion).
Bikerman
 Indi wrote: Is this a joke? Seriously, this is the stupidest science article i have read in months (that wasn't on the Onion).

LOL...that was my reaction. I'm presuming that the article is supposed to be about phase velocity of an em signal (in which case the article is so badly written it deserves the nearest junk pile).
Gagnar The Unruly
Hooray for science reporting!
Indi
You know what? i will grant mixing up the phase, group and signal velocities of a photon - that's just normal incompetence.

But this....

 Quote: Einstein predicted that particles and information can't travel faster than the speed of light — but phenomenon like radio waves? That's a different story, said Singleton, a Los Alamos National Laboratory Fellow.

Radio waves are a "different story" to light?!?!

And this:

 Quote: And other effects have also shown the possibility of phenomenon traveling faster than light, but Singleton's experiment has taken that to a new level, Singleton said. "If you take a laser and shine it on the moon and swing it rather gently, for example, the spot on the moon travels faster than the speed of light," Singleton said.

And this guy is a Fellow at LANL?!?!

No, we've left the realm of normal incompetence here. We are now in the twilight zone of incompetence - a dimension not of not only of incompetent sight and sound but of incompetent mind.
Bikerman
Yep - I was assuming that he was either misquoted or taken out of context, but if those are indeed his words then something is very badly wrong...
Gagnar The Unruly
Bad journalists take a lot of liberties, and I think it's way more likely that the physicist is being misrepresented than that he doen't know what he's talking about.
Indi
 Gagnar The Unruly wrote: Bad journalists take a lot of liberties, and I think it's way more likely that the physicist is being misrepresented than that he doen't know what he's talking about.

Well, i do grant the comment about radio waves being "a different story" to light is very likely the journalist misunderstanding the scientist.

But that comment about shining a laser on the moon was apparently a direct quote. It's hard to imagine how that could be taken out of context.
joostvane
The guys of Stargate Atlantis drop out of hyperspace to send out subspace radio signals.
SonLight
Indi wrote:
 Gagnar The Unruly wrote: Bad journalists take a lot of liberties, and I think it's way more likely that the physicist is being misrepresented than that he doen't know what he's talking about.

Well, i do grant the comment about radio waves being "a different story" to light is very likely the journalist misunderstanding the scientist.

But that comment about shining a laser on the moon was apparently a direct quote. It's hard to imagine how that could be taken out of context.

I think there may be a context issue here. I assume the physicist is giving an example of an experiment that could be misinterpreted as "moving faster than light". The movement of the light beam on the moon does not take place until after the light-time required for its cause (redirecting the beam) to occur on Earth and the effect to occur on the moon. If you look just at the light spot on the moon, though, the spot clearly can "move" "faster than light" to the new position. It is unfortunately easy to perform an experiment and misinterpret it this way. I hope the physicist was trying to point out that the example is NOT a violation of Einstein's principles of relativity.

He may well have been misquoted by the reporter. It sort of reminds me of the time my university installed a new mainframe computer, and a headline referred to it as an "electron queen".
Voodoocat
I found an article that clarifies the issue: Singleton has managed to change the polarization of radio waves faster than light, not make the wave travel faster than light. Here is the link: http://www.pi5.uni-stuttgart.de/mitarbeiter/pfau/physics-world-2008-10.pdf

Once again, you can't trust the news media to get anything right.
SonLight
 Voodoocat wrote: I found an article that clarifies the issue: Singleton has managed to change the polarization of radio waves faster than light, not make the wave travel faster than light. Here is the link: http://www.pi5.uni-stuttgart.de/mitarbeiter/pfau/physics-world-2008-10.pdf Once again, you can't trust the news media to get anything right.

Indeed, that article makes clear that no material object travels faster than light in the device, so Einstein's principles are not violated.

 Quote: Singleton’s team built and tested a proof-of- principle version of the device some five years ago (Physics World February 2003 p6). It consisted of a 2 m-long arc of dielectric with a series of electrodes that could, the researchers claim, change a pattern of polarization along the device faster than the speed of light (noting that no material object actually exceeds light speed).

The article goes on to say that nature apparently performs a similar "superluminal" feat in pulsars. The point is that a highly-focused beam can be sent, supposedly declining in intensity at the rate of 1/r (distance) instead of the ordinary 1/(r squared) decay of ordinary radio or flashlight beams.

There may be a catch though: one physicist suggests another law of nature may be violated by their proposal. If so, that would in no way invalidate the superluminal character of their devices, although it may make it useless for communications.
tukun2009manit
 Afaceinthematrix wrote: Theoretically, if you were traveling in a space ship at or near the speed of light going away from planet Earth, and you were somehow able to make a phone call to someone on earth, how would that work? Since you're getting farther away from Earth (c*time), would the amount of time that you've spent traveling be equal to the amount of time that it takes the signal to reach earth (assuming the waves from the phone travel at the speed of light)? Also, if someone was observing this, so time dilation was occurring, and you talked to that person on the phone, how would that work out? I've been spending a lot of time thinking about this lately and I thought I would ask people who know more about science than me...

optical fiber
The-Nisk
In reply to the first question regards the phonecall at near-light speed:
Indi mentioned the distortion of the signal by relativistic effects...I'm not quite sure what he meant, but I have an Idea and I think it's different to what I'm about to say (if it's the same, my bad).

Say we make a phonecall from a mobile phone at near-light speed, the signal emmited would probably be around 2.5 GHz. But since we're moving in respect to earth - the signal will be distorted by the Doppler Effect. This means that the signal being received will be of a different frequency and wavelength. And since we're traveling at the nearly the speed of light - this distortion will be massive, perhaps even incoherent to the receiver (since it will probably push either into some sort of low-frequency waves below radio waves or some very high frequency waves such as gama-radiation which could be lost amongst the background radiation. This was for emphasis purposes only, I didnt do the maths behind it so don't quote me on it)

Similar application was the red-shift of stars (or some name like that) - light that reaches us from stars moving away from us appears to be in the red-region, that was some of the evidence to sugest the expansion of the universe.

Also, phonecalls aren't necesaraly made at the speed of light - don't forget the computers on board the satelites re-routing etc.

And of course nothing can travel faster than light in this universe.
That's all. Please correct me if I was wrong, I don't mind. =]
Indi
 The-Nisk wrote: In reply to the first question regards the phonecall at near-light speed: Indi mentioned the distortion of the signal by relativistic effects...I'm not quite sure what he meant, but I have an Idea and I think it's different to what I'm about to say (if it's the same, my bad). Say we make a phonecall from a mobile phone at near-light speed, the signal emmited would probably be around 2.5 GHz. But since we're moving in respect to earth - the signal will be distorted by the Doppler Effect. This means that the signal being received will be of a different frequency and wavelength. And since we're traveling at the nearly the speed of light - this distortion will be massive, perhaps even incoherent to the receiver (since it will probably push either into some sort of low-frequency waves below radio waves or some very high frequency waves such as gama-radiation which could be lost amongst the background radiation. This was for emphasis purposes only, I didnt do the maths behind it so don't quote me on it) Similar application was the red-shift of stars (or some name like that) - light that reaches us from stars moving away from us appears to be in the red-region, that was some of the evidence to sugest the expansion of the universe. Also, phonecalls aren't necesaraly made at the speed of light - don't forget the computers on board the satelites re-routing etc. And of course nothing can travel faster than light in this universe. That's all. Please correct me if I was wrong, I don't mind. =]

No, it's correct, but you are forgetting the time dilation.

If a person on a ship travelling close to c relative to Earth calls Earth, before you consider Doppler, you have to consider the time dilation. The clocks on their ship are running slower than the clocks on Earth (according to the viewpoint of an Earth viewer). So before any signals are sent, the person on the ship will be speaking at a very slow rate, from the Earth viewer's point of view.

Then the signal gets sent, and you get Doppler effects as you describe.

Just remember to consider time dilation first (when the signal is being created) before worrying about the Doppler effect (when the signal is being sent).