Why the Universe may be Inherently Unstable

"The Cosmic Soup": An impressionist artist's view of the Cosmic Microwave Background (CMB) Radiation at the edge of our Local Universe. Artwork:: NaturPhilosophie

Exploring Vacuum Instability

Scientists are currently exploring the concept of vacuum instability.  What does this mean?  Well, they believe there is a chance that…  Billions of years from now, a new universe could open up into the present one and replace it.  It all depends on some very precise numbers related to the Higgs boson particle that researchers are currently trying to pin down.

If the calculation on vacuum instability holds, it would revive the old idea that the ‘Big Bang’ Universe we can observe today, is merely the latest version in a permanent cycle of events… 

 

Before the Planck Time

Nowadays, the fundamental interactions of Nature are still imperfectly described using two separate and mutually incompatible theories: the Standard Model of Particle Physics and General Relativity.  But it is worth noting that it may not always have been the case.

A branching diagram showing how the four fundamental forces of the Universe might have once originally been only one force.It is broadly theorised that before the Planck time, barely 10-43 seconds after the initial ‘Big Bang’ event, the strength of all four fundamental interactions must have been similar and that gravity would have played a significant role in particle interactions.

 

The Planck epoch is an era in traditional (non-inflationary) Big Bang cosmology during which the temperature is high enough that the four fundamental forceselectromagnetism, gravitation, weak nuclear interaction, and strong nuclear interaction — are all unified in one fundamental force.  Little is understood about physics at this temperature, and different theories propose different scenarios.

Traditional big bang cosmology predicts a gravitational singularity before this time, but this theory is based on General Relativity and is expected to break down due to quantum effects.

 

A diagram explaining the evolution of the Universe with cosmic times indicated.
Timeline of Universal Evolution (NASA Image)

The Universe So Far…

At an early time, the content of the Universe would have been made up of all the quarks and leptons, as well as their antiparticles.  Photons would have been present to mediate the fundamental interactions, and dark matter, including a slight excess of matter over antimatter.

In the first few hundred seconds, the physical conditions were such that they enabled nuclear fusion reactions, leading to the nucleosynthesis of primordial elements.

The Cosmic Microwave Background radiation (or CMB) observed at the present time, is the fossil light that was last scattered at a redshift z ~ 1100 (equivalent to a time t ~ 3-4 x 105) years.

The radiation originates from the last-scattering surface at this redshift value.  It displays intrinsic anisotropies in temperature at a level of a few parts in 105, resulting from density variation in the early Universe.  The observed high degree of uniformity of the CMB to the Horizon Problem, in which regions of last-scattering surface more than about 2º apart could not possibly have come into thermal equilibrium by the time that last scattering occurred…

 

Friedmann-Robertson-Walker Models of the Evolution of the Universe

At the heart of cosmological modelling, the Friedmann-Lemaître-Robertson-Walker metric is an important mathematical tool for understanding the possible evolution of the Universe: an exact solution to Einstein’s field equations of General Relativity.

It relies on the Cosmological Principle, which assumes a homogeneous and isotropic distribution of energy and momentum on the large scale.  It follows that the curvature of space must be uniform.

So far so good, it’s easy to comprehend, but…

Unlike what we perceive daily under the spatial constraints of our Euclidian minds, geometrical constructs can take on a whole new life.  In a three-dimensional space of positive curvature, space has a finite total volume.

Straight lines close back upon themselves, pairs of nearby parallel lines do converge and perhaps eventually meet.

 

Any plane triangle has interior angles that sum up to more than 180°.

The circumference of any circle is less than 2π times its radius!

Whereas in a space of negative curvature…  Uh…? !!

 

The FLRW metric describes an either expanding or contracting universe.  It contains a scale factor, which describes how the size of the Universe changes over time.

With the help of high-tech instrumentation such as Chandra X-Ray Observatory and the Planck Mission, observational measurements demonstrate that the temperature T of the CMB at any time t is inversely proportional to the scale factor at that particular time.

Thus,

T \propto {\frac {1}{R(t)}}

 

 

The FLRW models of possible ultimate fates of the Universe includes a range of cases that are:

  • closed,

  • critical,

  • open,

  • accelerating.

 

The FLRW models provide a natural interpretation of the redshifts of distant galaxies as cosmological redshifts caused by the stretching of light waves as they move through an expanding space.  The Einstein and de Sitter models are special cases.

 

A curve diagram explaining the different possible scenarios for the future of the Universe.Heat Death

Generally considered  the most likely, the “heat death” scenario occurs if the universe continues expanding as it has been.  Over a time scale of order 1014 years or less, existing stars burn out, stars are no longer created.

The Universe goes dark (Adams & Laughlin, 1997). 

Over a much longer time scale in the eras following this, the galaxy evaporates as the stellar remnants comprising it escape into space, and black holes evaporate via Hawking radiation.  In a Grand Unified Theory, proton decay after at least 1034 years will convert the remaining interstellar gas and stellar remnants into leptons and photons.  Some positrons and electrons then also recombine into photons.

Ultimately, the Universe reaches a high-entropy state consisting of a bath of particles and low-energy radiation.  Whether or not it eventually achieves thermodynamic equilibrium remains unknown (Adams & Laughlin, 1997).

Prior to the end of inflation (roughly 10-32 seconds after the Big Bang), evolutionary processes do not follow the traditional Big Bang timeline.  The Universe before the end of inflation is nearly a vacuum with a very low temperature, and it persists for much longer than 10-32 seconds.  Times from the end of inflation are based on the Big Bang time of the non-inflationary Big Bang model, not on the actual age of the Universe at that time, which cannot be determined in inflationary cosmology.

 

Big Crunch

If the dark energy density were negative or the Universe were closed, it would be theoretically possible that the expansion of the Universe could reverse.  Then, the Universe would contract towards a hot dense state.  This hot dense state is a required element of oscillatory universe scenarios, such as the cyclic model.  Although a Big Crunch does not necessarily imply an oscillatory Universe.

However, current observations appear to suggest that such a model is likely to be flawed, and that the expansion of the Universe is set to continue or even accelerate.

Observations of the CMB by the Wilkinson Microwave Anisotropy Probe suggest that the universe is spatially flat and has a significant amount of dark energy (Hinshaw et al. 2008), in which case, the Universe would continue to expand at an accelerating rate.  The acceleration of the Universe’s expansion has also been confirmed by observations of distant Type IA supernovae.

If, the dark energy is in the form of a cosmological constant, the expansion will eventually become exponential, with the size of the Universe doubling at a constant rate.

Should a ‘Big Crunch’ happen, it wouldn’t be for at least 100 billion years from now.  So, don’t worry…  The Sun and the Earth will be long gone by then.

What is really needed here is a ‘Theory of Everything’ that would account for all four fundamental interactions in a unified manner, and successfully describe the processes of the very early Universe.

 

An Oscillating Universe?

But there is a calculation that can be done under the constraints of the Standard Model, provided that the mass of the Higgs boson is known. 

Last year, a “Higgs-like” particle was first identified at the LHC (Large Hadron Collider).

Along with its energy field that pervades all space, the Higgs boson has long been sought out to help explain the existence of mass in the Universe, ultimately underpinning the workings of matter around us. 

According to Fermi Labs theoretician Joe Likken, a quantum fluctuation potentially creates a tiny bubble in the vacuum of the Universe.  And because of its lower-energy state, the bubble expands at the speed of light, sweeping everything before it.

A cyclical Universe might theoretically renew all of space every so often.

In 1931, Georges Lemaître was the first scientist to propose the expansion of the Universe was actually accelerating.  This was later confirmed observationally in the 1990s, with the observations of very distant Type IA supernova using the Hubble Space Telescope.

Such a scenario may have pleased Lemaître, who found the idea of a beginning in time “repugnant”:

“If the world has begun with a single quantum, the notions of space and time would altogether fail to have any meaning at the beginning; they would only begin to have a sensible meaning when the original quantum had been divided into a sufficient number of quanta.  If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time.”

 

A personal avatar thinking of our Universe. The caption reads: "What if the Universe is only just one wave?" Image: NaturPhilosophieThe Theory of the One-Electron Universe

As for Richard Feynman, he seemed happy to embrace another radical idea.  John Wheeler postulated in 1940 that there may exist only a single electron in the Universe, propagating through space and time in such a way as to appear in many places simultaneously.

In his 1965 Nobel Lecture, Feynman retold :

“As a by-product of this same view, I received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, “Feynman, I know why all electrons have the same charge and the same mass” “Why?” “Because, they are all the same electron!”  And, then he explained on the telephone, “suppose that the world lines which we were ordinarily considering before in time and space – instead of only going up in time were a tremendous knot, and then, when we cut through the knot, by the plane corresponding to a fixed time, we would see many, many world lines and that would represent many electrons, except for one thing.  If in one section this is an ordinary electron world line, in the section in which it reversed itself and is coming back from the future we have the wrong sign to the proper time – to the proper four velocities—and that’s equivalent to changing the sign of the charge, and, therefore, that part of a path would act like a positron.” “But, Professor”, I said, “there aren’t as many positrons as electrons.” “Well, maybe they are hidden in the protons or something”, he said”.

 

So what if…?