Multiverse Opponents Claim Nature Has No Sense of Scale

Monday, 25 August 2014 - 1:36PM
Astrophysics
Physics
Monday, 25 August 2014 - 1:36PM
Multiverse Opponents Claim Nature Has No Sense of Scale

The multiverse theory essentially arose as an explanation of our universe's fine-tuning for the existence of life. Rather than accept that our universe was "designed" or is "special" in any way, scientists reasoned that it must be one of many universes in an endless sea of universes, most of which are unfit for life. Now, physicists who subscribe to the scale symmetry theory of the universe are claiming that the universe doesn't have to be special, as long as it doesn't have mass or length. According to scale symmetry, at its most fundamental level, the universe has no sense of scale. 

 

In mathematics, scale symmetry refers to the idea that if an object's size is increased, it will retain the same properties. For all situations in which the objects are large enough to be governed by gravity, scale symmetry does not hold. This is why a candle blown up to the size of a tree would immediately collapse under its own weight, or why Godzilla is too big to exist in real life. But, according to some physicists, it may apply to fundamental particles that are not governed by gravity. This theory involves leaving mass and length out of the equations intended to describe the smallest particles of the universe. According to this theory, massless particles have interactions based on properties such as their charges, whether they are matter or antimatter, etc, and then eventually these interactions cause scale symmetry to "break," and the particles spontaneously acquire mass and length. 

 

The prevailing theory has been that the Higgs field, the existence of which was seemingly confirmed by the discovery of the Higgs boson, affords particles with mass when they pass through it, and that the Higgs boson is the only particle that begins its existence with mass. But some researchers are now arguing that even the Higgs boson doesn't have mass. 

 

"We're not in a position where we can afford to be particularly arrogant about our understanding of what the laws of nature must look like," said Michael Dine, a physics professor at the University of California, Santa Cruz. "Things that I might have been skeptical about before, I'm willing to entertain."

 

Although this flies in the face of generally accepted theories, we can't be "particularly arrogant" because some of those theories' predictions have failed to come to fruition. The mass of the Higgs boson is many orders of magnitude smaller than the Planck mass, which is the predicted maximum mass for such particles. This is called the hierarchy problem, as the standard model of physics expects that the quantum contributions from other particles would make the Higgs boson much bigger.

 

The hierarchy problem:

[Credit: Nelson Hsu/Quanta Magazine]

 

The Higgs is expected to be brought up towards the Planck mass as a result of other particles trying to make it closer to the largest value in the equation, or the Planck mass. "Quantum mechanics tries to make everybody democratic," explained theoretical physicist Joe Lykken, deputy director of Fermilab. "Particles will even each other out through quantum mechanical effects." 

 

In order to explain this, physicists came up with the idea of supersymmetry, which states that all fundamental particles have a twin with the same mass and same internal quantum number called a superpartner. According to supersymmetry, if for every particle the Higgs boson encountered, it also encountered its "twin," then the effects should essentially cancel out. If this theory were true, then it would explain why the Higgs boson is protected from quantum corrections. However, after 30 years of searching, no evidence of superparticles has ever been discovered. "That's what the Large Hadron Collider has been looking for, but it hasn't seen anything," said Savas Dimopoulos, a professor of particle physics at Stanford University. "Somehow, the Higgs is not protected."

 

Supersymmetry:

[Credit: Nelson Hsu/Quanta Magazine]

 

As theorists began to lose faith in the concept of supersymmetry, the fine-tuning problem came back to haunt them. If supersymmetry doesn't exist, then the Higgs' mass is not reduced by systematic interactions between symmetrical twins, but by random interactions that are somehow perfectly coordinated to afford the Higgs with the correct mass to allow for the formation of atoms. This apparent improbability of our universe led to the multiverse theory. 

 

Scale symmetry may serve as a solution to the incompatibility between the Standard Model's Higgs boson and gravity's larger particles. Generally, when trying to reconcile the two, theorists have assumed that both equations arose from the same starting point. But according to scale symmetry, they arose entirely separately, and essentially have nothing to do with each other. "The statement that gravity might not affect the Higgs mass is very revolutionary," Dimopoulos said.

 

Scale symmetry:

[Credit: Nelson Hsu/Quanta Magazine]

 

Particle physicists Alberto Salvio of the Autonomous University of Madrid and Alessandro Strumia of the University of Pisa propose a version of scale symmetry called agravity, which asserts that the Higgs and Planck masses arose separately and dynamically, as well as formulating a hypothesis for how this formation could have led to the exponential expansion of the universe after the Big Bang.

 

Although their theory solves the aforementioned problems with the prevailing theories, it adds one significant problem; it requires the existence of ghosts. Ghost particles have either negative energies or negative probabilities of existing, which are both as problematic as they sound. "Negative probabilities rule out the probabilistic interpretation of quantum mechanics, so that's a dreadful option," said Kelly Stelle, a theoretical particle physicist at Imperial College, London.

 

In spite of the widespread disdain for theories that include ghosts, Salvio and Strumia insist that keeping an open mind is key, especially considering that more popular theories have not panned out yet. When antimatter particles were first considered in equations, they seemed like negative energy," Strumia said. "They seemed nonsense. Maybe these ghosts seem nonsense but one can find some sensible interpretation."

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