QED: Force of a Vacuum Explained

In summary, the conversation discusses the Casimir effect, which arises from the ground state energy of the quantized electromagnetic field. This effect causes an attractive force between two conducting plates due to changes in the number of allowed modes in the space between them. The calculation for this force is more complicated and can be explained through virtual particles. However, the dominant contribution of the force does not require any reference to QED or the vacuum.
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nhmllr
185
1
So this is a decent series of videos introducing QED
http://www.youtube.com/watch?v=i8O_yQHxQos&feature=related
At 7:05, the host starts talking about the force that a vacuum creates, but doesn't elaborate further. What force is this? Are they attracting the plates through electromagnetism? Or is it the gravity of the antiparticles?
 
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The Casimir force is an effect that arises due to the ground state energy of the quantized electromagnetic field. Conceptually it works like this:

Each frequency mode of the electromagnetic field is treated like a quantum harmonic oscillator. So,therefore, each mode has a non zero ground state energy.

Now, let's place two conducting planes in our space. The electromagnetic field has to satisfy specific boundary conditions in the area between the plates, which alter the number of modes that are allowed to exist in that area. This changes the ground state energy of the field in a way that depends on the spacing between the plates.

Working through the calculation shows that the ground state energy gets lower as the plates are moved closer together. Since the system will want to minimize the total energy, this results in the attractive Casimir force between two conducting plates.

Of course, the calculation is a bit more complicated than this description makes it seem. Technically, the ground state energy of the electromagnetic field is infinite, so a regulator needs to be introduced, but conceptually it works as described above.
Some references for more details if you are interested:

The wiki article on the Casimir force actually runs through an outline of the calculation for two plane conductors. http://en.wikipedia.org/wiki/Casimir_effect

Also, Tony Zee's "QFT in a Nutshell" Chapter I.9. This is a short overview of the origin of the Casimir force at the level of a senior undergraduate who has had a course in quantum mechancs.

I should note that the Casimir force can also be explained in terms of virtual particles. However, I am not as familiar with that approach, so I'll let someone else give the details.
 
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The dominant contribution of the Casimir force is the standard molecular dispersion interaction, which does not require any reference to QED or the vacuum at all. See this thread:
https://www.physicsforums.com/showthread.php?t=484739
While there are some QED corrections to that force, they are tiny in magnitude and are not responsible for the presence of the force.
 

FAQ: QED: Force of a Vacuum Explained

1. What is QED and how does it explain the force of a vacuum?

QED, or Quantum Electrodynamics, is a quantum field theory that describes the interactions between particles and electromagnetic fields. It explains the force of a vacuum by showing that even in empty space, there are virtual particles that constantly pop in and out of existence, creating a fluctuating electromagnetic field that can exert a force on objects.

2. How was the force of a vacuum first discovered?

The force of a vacuum was first discovered through experiments with the Casimir effect. This effect shows that two uncharged metal plates placed very close together in a vacuum will experience a force that pushes them together. This force is caused by the fluctuating electromagnetic field between the plates.

3. Can the force of a vacuum be manipulated or controlled?

Currently, there is no known way to manipulate or control the force of a vacuum. However, scientists are constantly researching and experimenting with ways to harness the force of a vacuum for potential applications in technology and energy production.

4. Is the force of a vacuum the same everywhere in the universe?

According to current theories, the force of a vacuum should be the same everywhere in the universe. However, there are some areas of debate and ongoing research into potential variations in the force of a vacuum, particularly in extremely dense regions of space.

5. How does the force of a vacuum relate to other fundamental forces in the universe?

The force of a vacuum, or vacuum energy, is often considered to be the fifth fundamental force, along with gravity, electromagnetism, the strong nuclear force, and the weak nuclear force. However, unlike the other forces which are governed by specific laws and equations, the force of a vacuum is still not fully understood and is a subject of ongoing research and debate.

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