Death By Vacuum

As an astrophysicist, this has GOT to be one of my favorite ‘fringe’ topics in physics. There’s a long preamble story behind it, though!

The discovery of the Higgs Boson with a mass of 126 GeV, about 130 times more massive than a proton, was an exciting event back in 2012. By that time we had a reasonably complete Standard Model of how particles and fields operated in Nature to create everything from a uranium atom and a rainbow, to lighting the interior of our sun. A key ingredient was a brand new fundamental field in nature, and its associated particle called the Higgs boson. The Standard Model says that all fundamental particles in Nature have absolutely no mass, but they all interact with the Higgs field. Depending on how strong this interaction, like swimming through a container of molasses, they gain different amounts of mass. But the existence of this Higgs field has led to some deep concerns about our world that go well beyond how this particle creates the physical property we call mass.

In a nutshell, according to the Standard Model, all particles interact with the ever-present Higgs field, which permeates all space. For example, the W-particles interact very strongly with the Higgs field and gain the most mass, while photons interact not at all, remain massless.

The Higgs particles come from the Higgs field, which as I said is present in every cubic centimeter of space in our universe. That’s why electrons in the farthest galaxy have the same mass as those here on Earth. But Higgs particles can also interact with each other. This produces a very interesting effect, like the tension in a stretched spring. A cubic centimeter of space anywhere in the universe is not at all perfectly empty, and actually has a potential energy ‘stress’ associated with it. This potential energy is  related to just how massive the Higgs boson is. You can draw a curve like the one below that shows the vacuum energy  and how it changes with the Higgs particle mass:

Now the Higgs mass actually changes as the universe expands and cools. When the universe was very hot, the curve looked like the one on the right, and the mass of the Higgs was zero at the bottom of the curve. As the universe expanded and cooled, this Higgs interaction curve turned into the one on the left, which shows that the mass of the Higgs is now X0 or 126 GeV. Note, the Higgs mass represented by the red ball used to be zero, but ‘rolled down’ into the lower-energy pit as the universe cooled.

The Higgs energy curve shows a very stable situation for ‘empty’ space at its lowest energy (green balls) because there is a big energy wall between where the field is today, and where it used to be (red ball). That means that if you pumped a bit of energy into empty space by colliding two particles there, it would not suddenly turn space into the roaring hot house of the Higgs field at the top of this curve.

We don’t actually know exactly what the Higgs curve looks like, but physicists have been able to make models of many alternative versions of the above curve to test out how stable the vacuum is. What they  found is something very interesting.

The many different kinds of Higgs vacuua can be defined  by using two masses: the Higgs mass and the mass of the top quark. Mathematically, you can then vary the values for the Higgs boson and the Top quark and see what happens to the stability of the vacuum. The results are summarized in the plot below.

The big surprise is that, from the observed mass of the Higgs boson and our top quark shown in the small box, their values are consistent with our space being inside a very narrow zone of what is called meta-stability. We do not seem to be living in a universe where we can expect space to be perfectly stable. What does THAT mean? It does sound rather ominous that empty space can be unstable!

What it means is that, at least in principle, if you collided particles with enough energy that they literally blow-torched a small region of space, this could change the Higgs mass enough that the results could be catastrophic. Even though the collision region is smaller than an atom, once created, it could expand at the speed of light like an inflating bubble. The interior would be a region of space with new physics, and new masses for all of the fundamental particles and forces. The surface of this bubble would be a maelstrom of high-energy collisions leaking out of empty space! You wouldn’t see the wall of this bubble coming. The walls can contain a huge amount of energy, so you would be incinerated as the bubble wall ploughed through you.

Of course the world is not that simple. These are all calculations based on the Standard Model, which may be incomplete. Also, we know that cosmic rays collide with Earth’s atmosphere at energies far beyond anything we will ever achieve…and we are still here.

So sit back and relax and try not to worry too much about Death By Vacuum.

Then again…

 

Return here on Wednesday, February 22 for my next blog!

3 thoughts on “Death By Vacuum”

  1. Feynman, in six not so easy pieces, stated that the equations of relativity were consistent with the concept that mass was enhanced at relativistic velocities, although this concept was regarded as not generally accepted, as it is easy to obtain the Lorentz contraction factor by geometry and by assuming c is constant. But, wild thought for the day, suppose the mass enhancement is real and is due to the velocity with which the particle travels through the Higgs field, which, being uniform in all directions, is effectively having the property of the luminiferous aether relativity was supposed to get rid of.

    Back to more standard thinking, if the Higgs mass changes as the Universe expands, wouldn’t the masses of the elementary particles change? I apologise if (a) that is too simple and I just overlooked something, or (b) it is too complicated.

    1. Hi Ian! At my age I do not have time anymore to entertain ‘non standard’ theories that are not Lorentz-invariant. The Higgs field does not vary with the expansion because that idea has been tested by looking at quantum systems since shortly before the era of nucleosynthesis to the present time, with no significant variation in elementary particle masses during this time. Although the Higgs field is a scalar field just like the ‘dark energy field’ seems to be, it does not behave the same way, apparently. DE is only seen at cosmological or galactic scales. The Higgs field is present everywhere, and we can create Higgs particles from it at will and study their interactions. DE may not really be a field at all, but simply a non-zero vacuum energy contribution that is not exactly compensated by other ‘zero-point’ fields. We don’t really know, but for the Higgs we know quite a lot.

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