The Quantum Universe

Arrows of Time
As far as we know, the fundamental dynamical laws are time neutral --- preferring no direction of time over another. Yet our universe exhibits a number of `arrows of time' --- general phenomena that distinguish directions in time. There is the thermodynamic arrow of time --- the fact that presently isolated systems are mostly evolving towards equilibrium in the same direction of time. There is the electromagnetic arrow of time --- electromagnetic radiation is retarded. 

There is the psychological arrow of time --- we remember the past, experience the present, and predict the future. There are the arrows of time supplied by the expansion of the universe and the growth of inhomogeneity. And then, there is the quantum mechanical arrow of time defined in Copenhagen quantum mechanics by the direction in time the wave function of a subsystem is reduced on measurement. The papers below in various ways show how arrows of time arise in quantum cosmology from asymmetries in quantum conditions that specify our universe even though the dynamical laws are time neutral.   READ MORE...

Our Preordained Universe

Was there ever any choice in the Universe being as it is? Albert Einstein could have been wondering about this when he remarked to mathematician Ernst Strauss: “What I’m really interested in is whether God could have made the world in a different way; that is, whether the necessity of logical simplicity leaves any freedom at all.”

US physicist James Hartle, who died earlier this year aged 83, made seminal contributions to this continuing debate. Early in the twentieth century, the advent of quantum theory seemed to have blown out of the water ideas from classical physics that the evolution of the Universe is ‘deterministic’.

Hartle contributed to a remarkable proposal that, if correct, completely reverses a conventional story about determinism’s rise with classical physics, and its subsequent fall with quantum theory. A quantum Universe might, in fact, be more deterministic than a classical one — and for all its apparent uncertainties, quantum theory might better explain why the Universe is the one it is, and not some other version.  READ MORE...

Exploring the Quantum Universe

After a multi-year review, the U.S. particle physics community has announced its vision for research spanning the next five to ten years. The various projects could, if funded, help researchers develop a much better understanding of the laws of nature.

The recommendations were released in a report called “Exploring the Quantum Universe: Pathways to Innovation and Discovery in Particle Physics.” It was written by the Particle Physics Projects Prioritization Panel (P5), a sub-panel of the High Energy Physics Advisory Panel (HEPAP), and will be submitted to funding agencies like the U.S. Department of Energy Office of Science and the Natioce Foundation to guide their funding decisions over the next decade.  READ MORE...

Quantum Universe Inside an Atom

In many ways, the quest for what's truly fundamental in our Universe is the story of probing the Universe on smaller scales and at higher energies.

By going inside the atom, we revealed the atomic nucleus, its constituent protons and neutrons, and the quarks and gluons inside, plus many other spectacular features.

It's through this investigation of the subatomic world that we've revealed the elementary building blocks of our Universe and the rules that allow them to bind together to compose our cosmic reality.

If you wanted to uncover the secrets of the Universe for yourself, all you’d have to do is interrogate the Universe until it revealed the answers in a way you could comprehend them. 

When any two quanta of energy interact — irrespective of their properties, including whether they’re particles or antiparticles, massive or massless, fermions or bosons, etc. — the result of that interaction has the potential to inform you about the underlying laws and rules that the system has to obey. 

If we knew all the possible outcomes of any interaction, including what their relative probabilities were, then and only then would we claim to have some understanding of what was going on. Being quantitative in precisely this fashion, asking not only “what happens” but also “by how much” and “how often,” is what makes physics the robust science that it is.

Quite surprisingly, everything that we know about the Universe can, in some way, be traced back to the most humble of all the entities we know of: an atom. 

An atom remains the smallest unit of matter we know of that still retains the unique characteristics and properties that apply to the macroscopic world, including the physical and chemical properties of matter. And yet, an atom is a fundamentally quantum entity, with its own energy levels, properties, and conservation laws. 

Moreover, even the humble atom couples to all four of the known fundamental forces. In a very real way, all of physics is on display, even inside a single atom. Here’s what they can tell us about the Universe.   READ MORE...