Weakless Universe
Encyclopedia
The Weakless Universe is a hypothetical universe
that contains no weak interaction
s, but is otherwise very similar to our own universe.
In particular, the Weakless Universe is constructed to have nuclear physics
and chemistry
identical to standard nuclear physics and chemistry. The dynamics of the Weakless Universe includes a period of big bang
nuclear synthesis
, star
formation, stars that burn for billions of years, stellar nuclear synthesis of heavy elements and also supernova
e that distribute the heavy elements into the interstellar medium.
. A theory should ideally explain why the weak interaction is 32 orders of magnitude stronger than gravity; this is known as the hierarchy problem
.
There are various models that address the hierarchy problem in a dynamical and natural way, for example, supersymmetry
, technicolor
, warped extra dimensions
, etc. An alternative approach to explaining the hierarchy problem is to invoke the anthropic principle
. Within this approach one assumes that there are many other patches of the Universe (or Multiverse
) in which physics is very different. In particular one can assume that the "landscape" of universes contains ones where the weak force has a different strength compared to our own. In such a scenario observers would presumably evolve wherever they can. If the observed strength of the weak force is then vital for the emergence of observers, this would explain why the weak force is indeed observed with this strength. It was indeed argued by Barr and others that if one only allows the electroweak symmetry breaking scale to vary between universes, keeping all other parameters fixed,
atomic physics would change in ways that would not allow life as we know it.
Anthropic arguments have recently been boosted by the realization that string theory has many solutions, or vacua, dubbed the string landscape, and by Weinberg
's prediction of the cosmological constant by anthropic reasoning.
The hypothetical weak interaction-less universe is meant to serve as a counter example to the anthropic approach to the hierarchy problem. In the weakless universe other parameters are varied as the electroweak breaking scale is changed.
Indeed, string theory implies that the landscape is very big and diverse. The seeming habitability of the Weakless Universe implies that one cannot explain the hierarchy problem by anthropic reasoning alone, and that one must make strong assumptions about the available vacua in the landscape.
to helium, which proceeds through strong interactions. The high initial deuterium/hydrogen ratio (~ by mass) is arranged by simply reducing the overall baryon/photon ratio, which allows the BBN deuterium to be produced at a lower temperature, where the Coulomb barrier then protects it from immediate fusion into .
Another potential problem for a Weakless Universe is that supernova explosions are necessarily neutrinoless. The resulting efficiency of production and dispersion of heavy elements (in particular, oxygen) into the interstellar medium for subsequent incorporation into habitable planets has been questioned by Clavelli and White (see below).
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
that contains no weak interaction
Weak interaction
Weak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
s, but is otherwise very similar to our own universe.
In particular, the Weakless Universe is constructed to have nuclear physics
Nuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
and chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
identical to standard nuclear physics and chemistry. The dynamics of the Weakless Universe includes a period of big bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
nuclear synthesis
Nucleosynthesis
Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
, star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
formation, stars that burn for billions of years, stellar nuclear synthesis of heavy elements and also supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
e that distribute the heavy elements into the interstellar medium.
Motivation and Anthropics
The strength of the weak interaction is an outstanding problem in modern particle physicsParticle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
. A theory should ideally explain why the weak interaction is 32 orders of magnitude stronger than gravity; this is known as the hierarchy problem
Hierarchy problem
In theoretical physics, a hierarchy problem occurs when the fundamental parameters of some Lagrangian are vastly different than the parameters measured by experiment. This can happen because measured parameters are related to the fundamental parameters by a prescription known as renormalization...
.
There are various models that address the hierarchy problem in a dynamical and natural way, for example, supersymmetry
Supersymmetry
In particle physics, supersymmetry is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known as superpartners...
, technicolor
Technicolor (physics)
Technicolor theories are models of physics beyond the standard model that address electroweak symmetry breaking, the mechanism through which elementary particles acquire masses...
, warped extra dimensions
Randall-Sundrum model
In physics, Randall–Sundrum models imagine that the real world is a higher-dimensional Universe described by warped geometry...
, etc. An alternative approach to explaining the hierarchy problem is to invoke the anthropic principle
Anthropic principle
In astrophysics and cosmology, the anthropic principle is the philosophical argument that observations of the physical Universe must be compatible with the conscious life that observes it. Some proponents of the argument reason that it explains why the Universe has the age and the fundamental...
. Within this approach one assumes that there are many other patches of the Universe (or Multiverse
Multiverse (science)
The multiverse is the hypothetical set of multiple possible universes that together comprise everything that exists and can exist: the entirety of space, time, matter, and energy as well as the physical laws and constants that describe them...
) in which physics is very different. In particular one can assume that the "landscape" of universes contains ones where the weak force has a different strength compared to our own. In such a scenario observers would presumably evolve wherever they can. If the observed strength of the weak force is then vital for the emergence of observers, this would explain why the weak force is indeed observed with this strength. It was indeed argued by Barr and others that if one only allows the electroweak symmetry breaking scale to vary between universes, keeping all other parameters fixed,
atomic physics would change in ways that would not allow life as we know it.
Anthropic arguments have recently been boosted by the realization that string theory has many solutions, or vacua, dubbed the string landscape, and by Weinberg
Steven Weinberg
Steven Weinberg is an American theoretical physicist and Nobel laureate in Physics for his contributions with Abdus Salam and Sheldon Glashow to the unification of the weak force and electromagnetic interaction between elementary particles....
's prediction of the cosmological constant by anthropic reasoning.
The hypothetical weak interaction-less universe is meant to serve as a counter example to the anthropic approach to the hierarchy problem. In the weakless universe other parameters are varied as the electroweak breaking scale is changed.
Indeed, string theory implies that the landscape is very big and diverse. The seeming habitability of the Weakless Universe implies that one cannot explain the hierarchy problem by anthropic reasoning alone, and that one must make strong assumptions about the available vacua in the landscape.
Weakless stars
Perhaps the biggest obstacle for a habitable Weakless Universe is the necessary existence of stars. Our sun works through burning two protons to deuterium, which proceeds through weak interactions. In the Weakless Universe of Harnik, et al. (see below) this is overcome by ensuring a high primordial deuterium/hydrogen ratio during Big Bang Nucleosynthesis (BBN). This permits long-lived stars fueled by direct deuterium-proton burningDeuterium burning
Deuterium burning is a nuclear fusion reaction that occurs in stars and some substellar objects, in which a deuterium nucleus and a proton combine to form a helium-3 nucleus...
to helium, which proceeds through strong interactions. The high initial deuterium/hydrogen ratio (~ by mass) is arranged by simply reducing the overall baryon/photon ratio, which allows the BBN deuterium to be produced at a lower temperature, where the Coulomb barrier then protects it from immediate fusion into .
Another potential problem for a Weakless Universe is that supernova explosions are necessarily neutrinoless. The resulting efficiency of production and dispersion of heavy elements (in particular, oxygen) into the interstellar medium for subsequent incorporation into habitable planets has been questioned by Clavelli and White (see below).
External links
- Looking for Life in the Multiverse - Alejandro Jenkins, Gilad Perez - Scientific American Dec. 2009