Exactly why FTLC is impossible with entangled photons?

In summary, it is written that almost all physics books and courses state that entangled photons cannot be used for faster than light communication. The question of used entangled photons to communicate faster than light has been discussed before, but I was not able to understand why it is impossible. My goal is not to prove that many physicists and scientists are wrong about this, but to provide some superficial knowledge on quantum physics. According to my understanding, the probability for a photon to pass through a filter depends on the angle Φ between the photon and the filter polarization axis. Imagine some photons that are entangled and sent far away with Jack and Joe. They have agreed beforehand that they’ll send message to each other every 24 hours (or every 12 pm).
  • #36
Nugatory said:
Now suppose that Alice changes her angle to something else, which we'll call ##\theta##. The stream of photons reaching Bob is made up 50% of photons polarized along the angle ##\theta## and 50% polarized along the angle ##\theta+\pi/2##.

So when Alice changes her angle to Φ, and passes his photons through that filter, 50% pass through it and 50% don't. So The stream of photons reaching Bob is made up 50% of photons polarized along the angle Φ and 50% polarized along the angle Φ+1/2π.

Shouldn't it be that P=cos^2(Φ) of Alice's photons pass through his filter when he changes her angle to Φ?
 
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  • #37
Mentz114 said:
I don't understand why you two are arguing when you both must believe that a separable conditional probability ##P(xy|\alpha\beta)=P(x|\alpha)P(y|\beta)## cannot reproduce the predictions of QT ?

Beats me as well. All I am saying is the rules of normal probability theory are not respected in QM which is hardly surprising since it is a different probability model. If you want it to be like ordinary probability theory you need non-locality. But for some reason he thinks Bell has nothing to do with probability.

Thanks
Bill
 
  • #38
Karagoz said:
So when Alice changes her angle to Φ, and passes his photons through that filter, 50% pass through it and 50% don't. So The stream of photons reaching Bob is made up 50% of photons polarized along the angle Φ and 50% polarized along the angle Φ+1/2π.

Shouldn't it be that P=cos^2(Φ) of Alice's photons pass through his filter when he changes her angle to Φ?
If a photon does not pass a filter it is gone. All the photons that pass a polarizer are aligned to the polarizer angle.
 
  • #39
Karagoz said:
So when Alice changes her angle to Φ, and passes his photons through that filter, 50% pass through it and 50% don't. So The stream of photons reaching Bob is made up 50% of photons polarized along the angle Φ and 50% polarized along the angle Φ+1/2π.

Shouldn't it be that P=cos^2(Φ) of Alice's photons pass through his filter when he changes her angle to Φ?
The ones that arrive at Bob with polarization ##\phi+\pi/2## also encounter Bob's filter and contribute to the number passing through it. What is ##\cos^2(\phi+\pi/2)##?
 
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  • #40
Nugatory said:
The ones that arrive at Bob with polarization ##\phi+\pi/2## also encounter Bob's filter and contribute to the number passing through it. What is ##\cos^2(\phi+\pi/2)##?

We are talking aboit a new set of entangled photons when Alice changes his polarization filter. So almost same thing happens again.

Thanks, I think I got it if I'm not wrong.
 
  • #41
The question has been answered so its time to close it.

Thanks
Bill
 
<h2>1. What is FTLC and why is it impossible with entangled photons?</h2><p>FTLC stands for faster-than-light communication, which refers to the ability to send information or signals faster than the speed of light. This is impossible according to Einstein's theory of relativity, which states that the speed of light is the maximum speed at which all matter and information can travel. Entangled photons, which are particles of light that are connected in a special way, cannot be used for FTLC because they do not actually transmit information faster than the speed of light.</p><h2>2. How are photons entangled and why does this make FTLC impossible?</h2><p>Photons can become entangled when they are created or interact with each other in a certain way. This means that they share a special connection, even when they are physically separated. However, this connection does not allow for the transmission of information. The properties of entangled photons are only revealed when they are measured, and this measurement process does not allow for the transfer of information faster than the speed of light.</p><h2>3. Can entangled photons be used for any type of communication?</h2><p>No, entangled photons cannot be used for communication in the traditional sense. While they can be used for certain types of quantum communication, such as quantum teleportation, they cannot be used for sending messages or signals faster than the speed of light. This is because the measurement process involved in observing the entangled photons does not allow for the transfer of information.</p><h2>4. Are there any loopholes or exceptions that would allow for FTLC with entangled photons?</h2><p>No, there are no known loopholes or exceptions that would allow for FTLC with entangled photons. The laws of physics, specifically the theory of relativity, have been extensively tested and have consistently shown that the speed of light is the maximum speed at which information can travel. While there may be unknown phenomena or principles that could potentially allow for FTLC, there is currently no evidence to suggest that this is possible.</p><h2>5. How do scientists use entangled photons in their research, if they cannot be used for FTLC?</h2><p>Entangled photons are used in various fields of research, particularly in the field of quantum information and communication. They are used to study the fundamental properties of quantum mechanics and to develop new technologies, such as quantum computers and quantum encryption. While entangled photons cannot be used for FTLC, they have many other important applications in scientific research.</p>

1. What is FTLC and why is it impossible with entangled photons?

FTLC stands for faster-than-light communication, which refers to the ability to send information or signals faster than the speed of light. This is impossible according to Einstein's theory of relativity, which states that the speed of light is the maximum speed at which all matter and information can travel. Entangled photons, which are particles of light that are connected in a special way, cannot be used for FTLC because they do not actually transmit information faster than the speed of light.

2. How are photons entangled and why does this make FTLC impossible?

Photons can become entangled when they are created or interact with each other in a certain way. This means that they share a special connection, even when they are physically separated. However, this connection does not allow for the transmission of information. The properties of entangled photons are only revealed when they are measured, and this measurement process does not allow for the transfer of information faster than the speed of light.

3. Can entangled photons be used for any type of communication?

No, entangled photons cannot be used for communication in the traditional sense. While they can be used for certain types of quantum communication, such as quantum teleportation, they cannot be used for sending messages or signals faster than the speed of light. This is because the measurement process involved in observing the entangled photons does not allow for the transfer of information.

4. Are there any loopholes or exceptions that would allow for FTLC with entangled photons?

No, there are no known loopholes or exceptions that would allow for FTLC with entangled photons. The laws of physics, specifically the theory of relativity, have been extensively tested and have consistently shown that the speed of light is the maximum speed at which information can travel. While there may be unknown phenomena or principles that could potentially allow for FTLC, there is currently no evidence to suggest that this is possible.

5. How do scientists use entangled photons in their research, if they cannot be used for FTLC?

Entangled photons are used in various fields of research, particularly in the field of quantum information and communication. They are used to study the fundamental properties of quantum mechanics and to develop new technologies, such as quantum computers and quantum encryption. While entangled photons cannot be used for FTLC, they have many other important applications in scientific research.

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