3 ms·
The reason one is called static and involves 3d space and the other is called dynamic and involves time has nothing to do with stealing particles from the futur
by pudquick 15y ago
The reason one is called static and involves 3d space and the other is called dynamic and involves time has nothing to do with stealing particles from the future or creating a perpetual motion/energy machine.
What differs in these effects (in space and in time) is the electromagnetic modes of the vacuum near the mirror(s).
http://en.wikipedia.org/wiki/Normal_mode#Quantum_mechanics http://en.wikipedia.org/wiki/Normal_mode#Quantum_mechanics
It's all about creating a differential - and the effect this has for static vs. dynamic is different for each.
In the static effect, a differential is created in 3d space: two mirrors are perfectly placed in parallel to each other with a gap less than that of a photon's wavelength. In the vacuum fluctuation of space, virtual photons and anti-photon pairs are created and annihilate each other all the time - but this tiny gap keeps them from appearing between the mirrors. The end result is a difference in the modes between the mirrors (total lack of any activity) and outside them (normal vacuum fluctuations) which results in a pressure differential (in 3d space) pushing the plates together (the static effect).
In the dynamic effect, a differential is created due to a change over time: a mirror is moved at a velocity significantly close to the speed of light (in this case, around 5%). Around the mirror, as always, the vacuum contains photon and anti-photon pairs coming into existence and annihilating each other. With a fast enough moving mirror, the mirror can change the ability of the particles to annihilate each other. This represents a change in time over the nature of the vacuum / space where the particles appear.
Thought example: Prior to pair formation, there is no mirror at coordinate XYZ. Proton and anti-proton pair appears - and mirror is moving so fast, it is now present at point XYZ, between the proton and anti-proton, faster than the two could reach and annihilate each other. Now, instead of annihilation, the proton is reflected by the mirror.
This is the dynamical Casimir effect. It is a change, over time, in the nature of vacuum.
Yes, photons are being reflected ("created from nothing") in this effect - but so are anti-photons, which quickly find some other photon to interact with and annihilates the pair of them. There is no net gain of energy here - in fact quite a bit is spent keeping the mirror moving at high speeds.
- Karmadragon 15y agoThank you for your summary! It makes much more sense than the original article. It does leave me with a few questions, though. When you say the virtual particles are reflected, but quickly find another pair and annihilate each other, are they pairing wth normal photons? And because of the lack of anti-particles in our universe, isn't it more difficult for the photons to pair, meaning that if this experiment was scaled exponentially, the virtual photons would have an increasingly harder time pairing, becoming more abundant and living longer?
- ars 15y agoHis explanation is partially wrong, which is why you have questions. There is no such thing as an anti-photon, and if there was, then a photon anti-photon pair would annihilate to produce - more photons! Time in the quantum world is not completely logical, essentially these virtual particles (they are not real particles!!) can not appear unless they already managed to annihilate and vanish (i.e. the order of operations is not one way). The reason these photons do manage to exist is that the experiment provided the energy necessary before the particles appeared. The "anti-photon" is not a real particle, and does not need to find another photon to annihilate with. It's more of a concept of energy, what it represents is missing energy, which needs to be provided in order for the partner (the regular photon to exist). The "missing/extra" energy pair can exist only for a short time, below the Heisenberg uncertainty limit. If, in some way, you disrupt the annihilation of missing and extra energy, the particles would not appear in the first place (that's that out of order business I was talking about). But since the experiment provided energy, the particles can appear, and then be split, and the "anti-photon" uses the energy of the experiment to not exist. You have probably heard of the momentum/location uncertainty pair - but there is another: it's time/energy. So the more exactly you know how much energy there is, the less you know about when it existed - that's why the particle can have this out of order behavior - time itself is not properly defined for it.
- adavies42 15y agoum, did you mean electrons and positrons? afaik photons are their own antiparticles....