# Casimir effect

#### vincenzosassone

First of all, I want to thank you all for your support that helped me to expand my knowledges. It's been a year by now that I'm here and my knowledges in astronomy greately increased from my start point (I knew little about astronomy).
Anyway, to reduce the lenght of the post that will be too long otherwise: what is the Casimir effect? I have read a thread where we were talking about it, but I didn't completely understand the whole topic...
I know the Casimir effect appears when two bodies in the vacuum space are very close to each other ( nanometers if I'm not mistaken). They eventually collide without any force applied. This is what I read and partially understand, but I have a question on it: isn't this the normal force of gravity working on them?
I know this may seem a stupid question, but I really can't understand this passage, I don't even know whether this is an example of the casimir effect or not, it's too complex this topic for me.

Catastrophe

#### Helio

First of all, I want to thank you all for your support that helped me to expand my knowledges. It's been a year by now that I'm here and my knowledges in astronomy greately increased from my start point (I knew little about astronomy).
Anyway, to reduce the lenght of the post that will be too long otherwise: what is the Casimir effect? I have read a thread where we were talking about it, but I didn't completely understand the whole topic...
I know the Casimir effect appears when two bodies in the vacuum space are very close to each other ( nanometers if I'm not mistaken). They eventually collide without any force applied. This is what I read and partially understand, but I have a question on it: isn't this the normal force of gravity working on them?
I know this may seem a stupid question, but I really can't understand this passage, I don't even know whether this is an example of the casimir effect or not, it's too complex this topic for me.
Yes, gravity doesn't go away, so it had to be taken into account to properly conduct the experiment.

So the experiment was to see if the rate at which they collided exceeded the rate that would occur after taking all normal phenomena into consideration. The hypothesis being tested was that virtual particles, if they exist, will produce more force from outside the plates than from inside the plates. This was predicted because there is more space outside the plates, which allows for a broader range of frequencies, if you like, that affect the probability of those particles coming and going, thus more would impact the outer part of the plates.

Well, that's my novice take on the experiment, so keep open to a better version of it.

#### vincenzosassone

Yes, gravity doesn't go away, so it had to be taken into account to properly conduct the experiment.

So the experiment was to see if the rate at which they collided exceeded the rate that would occur after taking all normal phenomena into consideration. The hypothesis being tested was that virtual particles, if they exist, will produce more force from outside the plates than from inside the plates. This was predicted because there is more space outside the plates, which allows for a broader range of frequencies, if you like, that affect the probability of those particles coming and going, thus more would impact the outer part of the plates.

Well, that's my novice take on the experiment, so keep open to a better version of it.
Thank you, I thought everything happened because of gravity...
This is a small but effective explanation!

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#### socratus

The Casimir effect showed that the cosmic vacuum is not empty space.

vincenzosassone

#### vincenzosassone

Yeah, if I understand correctly, the casimir effect interests a particular area where there is no matter unless two objects (two plates) close to each other about nanometers. These two plates will collide on each other ove time because of the discrepancy that is present between energy inside and outside the two plates. This discrepancy of energy must be a discrepancy of matter too thanks to Albert Einstein laws.
This energy is also interpretable as fluctuations.
well then, this is the greatest recap of the topic.

Catastrophe

#### socratus

This energy is also interpretable as fluctuations.
well then, this is the greatest recap of the topic.
cosmic vacuum fluctuations is still the great enigma of nature

vincenzosassone

#### Atlan0101

The stronger the crunch, the stronger the bulge, whichever the force. As to the one, it isn't called "electro" magnetism for no reason. Besides, "vacuum fluctuations" don't travel well. They don't do motion well. Their animation is fleeting. But there are terrific by-products to all that fleeting animation and all that fleeting animation is all over the place.

vincenzosassone

#### Catastrophe

##### "There never was a good war, or a bad peace."
Here are some videos:
PREVIEW
4:35
The Casimir Effect
6 Jun 2016

4 key moments in this video

*******

PREVIEW
16:07
The Casimir Effect
15 Jun 2012

10 key moments in this video

********

10:40
Casimir Effect & Black Holes - Sixty Symbols
20 Mar 2014

For what it's worth, I found the third 0ne easier to understand, and quicker. It also explains the Dynamic Casimir Effect, and its occurrence in black holes.

Cat

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#### Helio

Thanks Cat, that confirms and adds to my understanding of that experiment. "Not all infinities are equal" (more real numbers than integers) is worth quoting in the future.

#### Catastrophe

##### "There never was a good war, or a bad peace."
Helio: "Not all infinities are equal"

Grrrrrrrrrrrr! Now I've heard it all.

Shame he could not find some better wording.

Nevertheless, I did like the bottom video.

Cat

#### Helio

Helio: "Not all infinities are equal"

Grrrrrrrrrrrr! Now I've heard it all.

Shame he could not find some better wording.

Nevertheless, I did like the bottom video.

Cat
Yes, but it helps dealing with such things when you know that in many cases the limit to an infinite series can be shown to be a specific value, just not always.

#### Catastrophe

##### "There never was a good war, or a bad peace."
Why not just leave it at (for the purposes of that video) the suggestion that many more wavelengths are possible outside the plates than between them, because the very small distance between the plates can only accommodate a small number of complete waves. Most waves will not fit between the plates so cannot form. It is like a string between two points. You cannot have a standing wave (vibration) of 3.127 wavelengths. No need for infinities. Hence the greater number of waves outside (than between the plates) produces a pressure which pushes the plates together.

One could invoke the wave/particle nature, and say that the greater number of waves, viewed as particles produce pressure similar (by analogy) to the atoms in elementary gas laws explanations. A nice diagram would help. Convert all his wiggly lines into particles hitting the plates from outside and in.

I could probably word it more eloquently if I had the time, but I think the meaning is clear.

Cat

vincenzosassone

#### Helio

Why not just leave it at (for the purposes of that video) the suggestion that many more wavelengths are possible outside the plates than between them, because the very small distance between the plates can only accommodate a small number of complete waves. Most waves will not fit between the plates so cannot form. It is like a string between two points. You cannot have a standing wave (vibration) of 3.127 wavelengths. No need for infinities. Hence the greater number of waves outside (than between the plates) produces a pressure which pushes the plates together.
Your point is the main one. I get their clever use of infinities, but it raises questions that need not get tossed into the confusion. What does an infinitely long wavelength look like? But that isn't really what they are saying, but that there are an infinite no. of fractional values outside the plates vs. inside, though the use of "infinite" is unnecessary, and may not even be valid, because the Planck limit may produce a limit on the number of actual wavelengths.

I could probably word it more eloquently if I had the time, but I think the meaning is clear.
It's still a little unclear to me since do virtual particles last long enough to form a standing wave? Why does a standing wave need to be required?

#### Catastrophe

##### "There never was a good war, or a bad peace."
Helio, you know that I am no expert, and try to help by clarifying some issues as best I can. I am not the greatest fan of quantum matters, but I think the point he is trying to make is that the number of wavelengths between the two plates is limited because they have to go back and forth between the two plates. OK, standing waves may not be the best expression, but I think he is suggesting that if you did not have a wavelength corresponding to whole values they would not reflect between the plates as 'whole' waves. Wavelengths have to be integral fractions of the distance between the plates. Once it is established that the number of wavelengths fitting between the plates is limited compared with outside the plates, the pressure difference follows, and the effect explained.

Cat

Helio

#### Helio

Helio, you know that I am no expert, and try to help by clarifying some issues as best I can. I am not the greatest fan of quantum matters, but I think the point he is trying to make is that the number of wavelengths between the two plates is limited because they have to go back and forth between the two plates. OK, standing waves may not be the best expression, but I think he is suggesting that if you did not have a wavelength corresponding to whole values they would not reflect between the plates as 'whole' waves. Wavelengths have to be integral fractions of the distance between the plates. Once it is established that the number of wavelengths fitting between the plates is limited compared with outside the plates, the pressure difference follows, and the effect explained.
[I realized I hadn't dug into this....]

Here is a site that may simplify things.

"Casimir realised that between two plates, only those virtual photons whose wavelengths fit a whole number of times into the gap should be counted when calculating the vacuum energy."

So, in a tiny gap between plates, only tiny wavelengths (short wave photons that serve to push outward) are allowed, whereas outside the plates all wavelengths are allowed (the full spectrum of photons pushing the plates inward).