F a transmiter for arguments sake, fitted in a satalite orbiting the earth

  • Context: High School 
  • Thread starter Thread starter wolram
  • Start date Start date
  • Tags Tags
    Earth
Click For Summary

Discussion Overview

The discussion revolves around the behavior of signals transmitted from satellites, specifically focusing on the interference of waves that are 180 degrees out of phase. Participants explore whether such signals would cancel each other out upon meeting and whether this principle applies to all types of waves.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions if two transmitters sending identical signals 180 degrees out of phase would cancel each other at the point of meeting, suggesting this might apply to all waves.
  • Another participant asserts that the signals would continue independently and would not cancel each other out, emphasizing the low probability of interaction between photons over large distances.
  • Some participants argue that light waves can interfere with each other and suggest that interference applies to all types of waves, including sound and ocean waves.
  • A participant raises the idea that distance is a significant factor in interference, questioning how far apart transmitters would need to be to avoid interference.
  • One participant introduces the concept of using lasers to demonstrate interference, noting that it is easier to achieve with sound due to longer wavelengths compared to light.
  • Another participant mentions the GPS system, explaining that it uses signals from multiple satellites and that while interference occurs, each signal remains unaffected after points of interference.
  • A reference is made to a quantum mechanical effect related to light sources being in phase, suggesting that even distant sources can combine their light effectively.
  • A hypothetical scenario is posed regarding two laser beams focused at a perfect reflector, questioning whether there would be any reflected light if they are out of phase.

Areas of Agreement / Disagreement

Participants express differing views on whether signals can cancel each other out and the conditions under which interference occurs. There is no consensus on the implications of distance or the specific mechanics of interference in various contexts.

Contextual Notes

Participants note that the interaction of light waves and the conditions for interference can be complex, with factors such as distance and wavelength playing significant roles. The discussion includes hypothetical scenarios that may not fully account for practical limitations or assumptions.

wolram
Gold Member
Dearly Missed
Messages
4,411
Reaction score
551
im not sure how to pose this question, my ist try.
if a transmiter for arguments sake, fitted in a satalite orbiting the Earth sent a 1mgh sgnal say for 10 secs and an identicle transmiter some distance away transmited an identicle signal but 180 deg phase difference would they cancel each other at point of meeting, if ansewer is yes then is this true for all waves ?
please exuse non formalities.
 
Last edited by a moderator:
Physics news on Phys.org


Originally posted by wolram
im not sure how to pose this question, my ist try.
if a transmiter for arguments sake, fitted in a satalite orbiting the Earth sent a 1mgh sgnal say for 10 secs and an identicle transmiter some distance away transmited an identicle signal but 180 deg phase difference would they cancel each other at point of meeting, if ansewer is yes then is this true for all waves ?
please exuse non formalities.
No, each would continue on, independent of the other.
 


Originally posted by Labguy
No, each would continue on, independent of the other.
Why not? Light waves are certainly capable of interfering with each other. I think they WOULD cancel each other out.

And yes, interference works for all waves. Light, sound waves, waves on the ocean, waves on a string, etc.
 


Originally posted by russ_watters
Why not? Light waves are certainly capable of interfering with each other. I think they WOULD cancel each other out.

And yes, interference works for all waves. Light, sound waves, waves on the ocean, waves on a string, etc.
The odds of photons (or any EMR) transmitted miles away from each other actually interacting is "astronomically" small. Imagine how our radios would sound if they did. Also, the "folded" optical paths in some telescope designs would see what? Black?
 
please elaborate labguy russ
 
Originally posted by wolram
please elaborate labguy russ
My "elaboration" is easy. There would be no "point of meeting", and the odds of photon interaction would be virtually nil.
 
now i see distance is major factor, in a confined space there could be interferance but how far away from each other would trasmiters have to be to guarantee no interferance? transmiters rated at 100W.
 


Originally posted by Labguy
The odds of photons (or any EMR) transmitted miles away from each other actually interacting is "astronomically" small. Imagine how our radios would sound if they did. Also, the "folded" optical paths in some telescope designs would see what? Black?
It was a hypothetical, Labguy. Of course the possibility is small. Maybe a better hypothetical would be using a laser. That way you have a LOT of photons traveling in the same direction. Shine another laser in the same direction out of phase and they WOULD cancel out.

now i see distance is major factor, in a confined space there could be interferance but how far away from each other would trasmiters have to be to guarantee no interferance? transmiters rated at 100W.
Distance isn't really much of an issue. The issue is can you make the beams cross out of phase? Its a piece of cake with sound, since the wavelengths are pretty long, but its tough for light since the wavelenghts are very small.
 
Isn't this idea the basis for the GPS system? You recive signals from 3 separate satilites, compare the phases and determine your postion.

Yes, the signals would interfer but, each signal would continue uneffected after the point or points of interference. At any point is space where the phase of the signals differ by 180deg there will be distructive interference, at points where the signals are in phase the signals will reinforce each other.
 
  • #10
There is something rather similar

I read in the Feynman lectures, but I couldn't find it in the index. I believe it's called the Hadley_Twiss_Brown Effect (delightfully British name) that says that if two light sources are located a small angular distance apart at the receiver, even though they may be far apart in space, the example used a street lamp and a star, the combined light will tend to be in phase. It's strictly a quantum mechanical effect due to the fact that photons are bosons.
 
  • #11
off to the Physics forum this goes!
 
  • #12
so, if 2 laserbeams one 180 degrees out of phase with the other are focused at a point one wave lengh in front of a perfect reflector, would there be no reflected light?
 
  • #13
Originally posted by Integral
Isn't this idea the basis for the GPS system? You recive signals from 3 separate satilites, compare the phases and determine your postion.

Yes, the signals would interfer but, each signal would continue uneffected after the point or points of interference. At any point is space where the phase of the signals differ by 180deg there will be distructive interference, at points where the signals are in phase the signals will reinforce each other.
I don't think GPS uses actual interference patterns, but instead compares coded signals. Similar, but not quite the same.

And your second part is correct. I didn't mean to apply that the waves would cancel and then cease to exist.