## Physics Questions People Ask Fermilab

Vacuum

You wrote:

I'm Stephen and I moderate a theoretical physics forum at physicsforums.com.

Is it possible to increase the probability that virtual particles will appear in a vacuum?

I was posed this question from a member and i do not have a definite answer in my reference materials. I would greatly appreciate any response as to how/why if the question has a yes answer.

Thank you for your time.

Regards,
Stephen J Hall, Theoretical Physics moderator

PS. if you are ever browsing the net and want to interact with some nice people who are all about learning, I'd like to cordially invite you to Physics Forums - Black Holes to the Speed of Light .

Dear Stephen:

Your question refers to the fact that "vacuum is not empty." As long as the properties of the vacuum are not violated (total electrical charge zero, etc), particles can appear for a short period of time and exist as so called virtual particles, just to disappear again within a time frame specified by Heisenberg's uncertainty principle. The typical process is pair production, in which a particle and its corresponding antiparticle appear; for example, an electron and its antiparticle called positron. (Since they have opposite electrical charges, the total zero charge of the vacuum is preserved.) The antiparticle is considered to be a negative energy state, a hole that the particle left in the "sea of unseen particles" that constitutes the vacuum.

You are wondering whether scientists can stimulate the production of virtual particles in vacuum. The answer is: No. Not without introducing particles into the vacuum.

All parameters that control the pair production in vacuum are beyond our control: the mass of the particles (the uncertainty principle favors the pair production of light particles rather than heavy ones), their interaction strengths, Planck's constant (which is essential in computing the probability how long the virtual particles will exist) and other related particle properties and physical constants.

We cannot heat a vacuum (heat requires the presence of real, not virtual particles) and have no other means of stimulating the production of virtual particles IN VACUUM. However, sending beams of particles into the vacuum (hence, destroying the vacuum) increases virtual pair production. Creating powerful collisions of particle beams, the chance of producing real and virtual particles greatly increases. (A real particle is a particle that doesn't violate any energy conservation rules, etc, and theoretically can exist forever. If an unstable particle, it may decay into lighter particles.)