What Are Virtual Particles? Dr. Paul Matt Sutter Helps Explain

As we’ve learned, black holes can evaporate over time thanks to the creation of virtual particles at the edge of the event horizon. Dr. Paul Matt Sutter returns to help us make sense of the science.

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Team: Fraser Cain – @fcain
Jason Harmer – @jasoncharmer
Chad Weber – [email protected]

Created by: Fraser Cain and Jason Harmer
Edited by: Chad Weber
Music: Left Spine Down – “X-Ray”

Sometimes I figure out the weak spot in my videos based on the emails and comments they receive.

One popular video we did was all about Stephen Hawking’s realization that black holes must evaporate over vast periods of time. We talked about the mechanism, and mentioned how there are these virtual particles that pop in and out of existence.

Normally these particles self annihilate, but at the edge of a black hole’s event horizon, one particle falls in, while another is free to wander the cosmos. Since you can’t create particles from nothing, the black hole needs to sacrifice a little bit of itself to buy this newly formed particle’s freedom.

But my short video wasn’t enough to clarify exactly what virtual particles are. Clearly, you all wanted more information. What are they? How are they detected? What does this mean for black holes?

In situations like this, when I know the actual Physics Police are watching, I like to call in a ringer. Once again, I’m going to go back and talk to my good friend, and actual working astrophysicist, Dr. Paul Matt Sutter. He has written papers on subjects like the Bayesian Analysis of Cosmic Dawn and MHD Simulations of Magnetic Outflows. He really knows his stuff.

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Fraser Cain:
Hey Paul, first question: What are virtual particles?

Paul Matt Sutter:
Alright. No pressure, Fraser. Okay, okay.

To get the concept of virtual particles you actually have to take a step back and think about the field, especially the electromagnetic field. In our current view of how the universe works all of space and time is filled up with this kind of background field. And this field can wibble and wabble around, and sometimes these wibbles and wabbles are like waves that propagate forward, and we call these waves photons or electromagnetic radiation, but sometimes it can just sit there and you know bloop bloop bloop, just you know pop fizzle in and out, or up and down, and kind of boil a little all on its own.

In fact all the time space is kind of wibbling/wabbling around this field even in a vacuum. A vacuum isn’t the absence of everything. The vacuum is just where this field is in its lowest energy state. But even though it’s in that lowest energy state, even though maybe on average there is nothing there. There’s nothing stopping it from just bloop bloop bloop you know bubbling around.

So actually the vacuum is kind of boiling with these fields. In particular the electromagnetic field which is what we are talking about right now.

And we know that photons, that light, can turn into particle, anti-particle pairs. It can turn into say an electron and a positron. It can just do this. It can happen to normal photons, and it can happen to these kind of temporary wibbly wobbly photons.

So sometimes a photon or sometimes the electromagnetic field can propagate from one place to another, and we call it a photon. And that photon can split off into a positron and an electron, and other times it can just wibble wobble kind of in place and then wibble wobble POP POP. It pops into a positron and an electron and then they crash into each other or whatever, and they just simmer back down. So, wibble wobble, pop pop, fizz fizz is kind of what’s going on in the vacuum all they time, and that’s the name we give these virtual particles are just the normal kind of background fuzz or background static to the vacuum.

Fraser:
Okay. So how do we see evidence for virtual particles?

Paul:
Yeah, great question. We know that the vacuum has an energy associated with it. We know that these virtual particles are always fizzing in and out of existence for a few reasons.

One is the transition of the electron in different states of the atom. If you excite the atom the electron pops up to a higher energy state. There is kind of no reason for that electron to pop back down to a lower energy state. It’s already there. It’s actually a stable state. There is no reason for it to leave unless there is little wibble wobbles in the electromagnetic field and it can giggle around that electron and knock it out of that higher energy state and send it crashing down into a lower state.