Can a Photon be thought of as a bit?

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Discussion Overview

The discussion revolves around the conceptualization of a photon in relation to information theory, specifically whether a photon can be considered a bit or a qubit. Participants explore the implications of a photon's speed and the nature of time in this context, touching on quantum states and the intrinsic properties of photons.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants suggest that since a photon travels at the speed of light, it exists in a state of emission or absorption, potentially making it a type of bit or qubit.
  • Others argue against this notion, stating that a photon has wavelength, which cannot be represented as a binary quantity.
  • One participant emphasizes that emission and absorption are not quantum states, challenging the idea that a photon can be in both states simultaneously.
  • Concerns are raised about the oversimplification of the statement "time does not exist for a photon," with references to intrinsic properties of photons that are observable.
  • Some participants question the meaningfulness of discussing time from a photon's perspective, noting that a photon does not have a rest frame and thus cannot have a defined proper time.
  • References are made to spacetime diagrams and the concept of null intervals, indicating that the behavior of photons is fundamentally different from that of particles with rest frames.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of photons and their relationship to time and information. The discussion remains unresolved, with no consensus on whether a photon can be considered a bit or qubit.

Contextual Notes

Participants highlight limitations in understanding the nature of time for photons, the dependence on definitions of quantum states, and the implications of spacetime intervals. These factors contribute to the complexity of the discussion.

hankaaron
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A photon is emitted and then absorbed. And since a photon travels at the speed of light, time does not exist. So that should mean that a photon is in either a state of emission or a state of absorption.

Doesn't that make a photon a type of bit?

Furthermore - if there is no time involved then would it be correct to say that a photon ican be in both states (Emission and Absorption) at the same time? Wouldn't it also make a photon a Qbit?
 
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Absolutely not. A photon has wavelength and that can't be represented as a binary quantity.
 
hankaaron said:
Furthermore - if there is no time involved then would it be correct to say that a photon ican be in both states (Emission and Absorption) at the same time? Wouldn't it also make a photon a Qbit?

Emission and absorption are not quantum states.

You should also not attempt to transform to the photon frame to arrive at the conclusion that a photon has "no time involved".

Zz.
 
And since a photon travels at the speed of light, time does not exist

If you recall intrinsic properties of photons, such as charge, mass and spin, ARE observables...as with matter particles...so that is an indicator 'time does not exist' is an oversimplification ...Somebody even said 'Eternity is not time at all for a photon.' Better to say time is not defined.

Doesn't that make a photon a type of bit?

Well, no, but the presence of a photon IS different than the absence or a photon...so THAT information is encoded as with all particles.

if there is no time involved then would it be correct to say that a photon ican be in both states (Emission and Absorption) at the same time? Wouldn't it also make a photon a Qbit?

nice try but alas, as you can probably tell, no...that would be too easy...

I kept a mathematical explanation of 'time does not exist for a photon' posted in these forums, but alas I cannot find it...I will look tomorrow...was from PeterDonis, I believe.
 
hankaaron said:
And since a photon travels at the speed of light, time does not exist.
For a photon, time does not exist? Tell that to the photon that took 8 minutes traveling at the speed of light from the sun to get here. Tell that to the photon that was emitted in the Big Bang and is just now being absorbed 13.8 billion years later. :biggrin:
 
Bill_K said:
For a photon, time does not exist? Tell that to the photon that took 8 minutes traveling at the speed of light from the sun to get here. Tell that to the photon that was emitted in the Big Bang and is just now being absorbed 13.8 billion years later. :biggrin:

Relatively- would it seem like 8 minutes or 13.8 billion years to the photon?
 
hankaaron said:
Relatively- would it seem like 8 minutes or 13.8 billion years to the photon?
What things might "seem like" to a photon is meaningless. A photon does not carry a pocket watch.

The quantity called proper time can be defined for particles - it's the time that elapses between two events in the particle's rest frame. But a photon does not have a rest frame, and proper time for a photon can't be defined.

What does have meaning is the coordinate time in some inertial frame. Yes, it's relative. :rolleyes: But the elapsed coordinate time between the photon's emission and absorption is what serves to separate the two events.
 
Related to Bill_k's comment:
But a photon does not have a rest frame, and proper time for a photon can't be defined.

is this, from a prior discussion alluding to spacetime diagrams:

The interval of a photon…is called a null interval because it is inherently different that either a timelike spacetime interval or a spacelike spacetime interval. We can neither measure it with either a clock or a ruler, neither can we characterize as either timelike or spacelike.

or equivalently,
The four momentum of the photon is a null vector.
says Roger Penrose in THE ROAD TO REALITY

Yes, here is the quote I referred to above which I like:
PeterDonis:
...photon worldlines contain multiple events. You can't use proper time to label the events, but you can use other affine parameters; and the fact that you can't use proper time to label the events does *not* mean that "they all happen at the same time".
 

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