Is There a Mirror World?

In case you are already puzzled, the above image is a logarithmic representation of the observable universe. Notable astronomical objects are annotated. Distance from Earth increases exponentially from center to edge. Celestial bodies were enlarged to appreciate their shapes. Rendered specially for Wikipedia.org by Pablo Carlos Budassi.

The Hubble Constant isn’t

What seemed a certainty when I was a physics undergrad has become less certain in the many intervening years.

The Hubble Constant (H0) is more like the Hubble Variant, with two precisely measured values which differ significantly depending on the technique used.

…the true value of the Hubble constant remains up for debate. Based on the fundamental physics that scientists believe has driven the evolution of the universe, the Hubble constant should be around 68 km/s/Mpc — but this doesn’t match up to observations of the actual stars and galaxies astronomers see around us. UChicago astronomer Wendy Freedman led a team that made a landmark measurement in 2001, which found a value of 72. — University of Chicago

That’s a difference of 5.9% and enough to make cosmologists quake.

That disparity has now reached a statistical significance of 5σ, which means that the disagreement is unlikely to be a chance fluke. Recently, Adam Riess at the Space Telescope Science Institute in Baltimore, US, and colleagues have established a Hubble-constant value of 73.04 ± 1.04 km/s per megaparsec (Mpc) via local observations. Meanwhile, data from the CMB, courtesy of the European Space Agency’s Planck satellite, instead yield 67.49 ± 0.53 km/s/Mpc. — Physics World

Which value is correct?

Pass.

Now recent research has floated the idea that the difference could be explained if the universe contains what is known as a mirror world dark sector.

The posited mirror world would contain copies of all existing fundamental particles. These would interact with each other through “mirror” versions of the known force particles, but with different masses and coupling strengths.

The new research relies on re-scaling at all points on the cosmic timescale both the cosmic expansion rate and the rate of photon scattering (essential for the generation of the cosmic microwave background radiation). This would have the effect of re-scaling the lengths and timescales needed resolve the range of values of the Hubble Constant.

It does however leave other problems unresolved, for example the rate of photon scattering.

The gravity problem

Gravity is considered to be much weaker than the other known fundamental forces and this has been an ongoing puzzle for many years — gravity cannot be included within the Standard Model of particle physics.

Each fundamental force has its own associated force-carrying particle called bosons. Specific kinds of bosons are responsible for the weak force, electromagnetic force and strong force.

In theories of quantum gravity, the graviton is the hypothetical quantum of gravity, an elementary particle that mediates the force of gravitational interaction. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity.

That’s the conundrum. From the point of view of symmetry, the graviton should exist. That would be neat and tidy and make me happy.

A hole

And that’s where we fall into a hole:

Gravity is the only fundamental force that physicists can currently describe without using force-carrying particles — space.com

Could this new research explain the problem?

They do not address it in their paper other than to suggest that the mirror set of standard-model-like particles would interact gravitationally with conventional matter.

KISS

I like to think of the universe as an elegant and basically simple entity. We seem to be developing ever more bizarre explanations.

The deeper we dig, the more complexity we uncover. I have a problem with the singularity of the Big Bang theory. And I believe — yes, belief, an unsupported idea — in symmetry. The mathematical complexity we have developed embraces symmetry: matter/antimatter, energy/dark energy, matter/dark matter and so on.

Wherefore art thou, graviton?

In its current form, the proposed scaling solution will not be the final explanation of the problem, as it incorrectly predicts the Universe’s relative abundances of deuterium and helium. The team says that solving that issue should be easier than solving the puzzle of the Hubble ‘Constant’.

I can’t help feeling that physics has gone down a rabbit hole and entered a warren.

There must be someway outta here…

The new research is published in Physical Review Letters.

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Canonical: This story was first published in Medium on 7 June 2022 edited, youtube link added.