Life on Mars?
Mars may have been a more favorable planet for life to get started. The bombardment of the planets by asteroids and comets can eject rocks into space, providing a mechanism for microbes to be transported from Mars to Earth (or vice versa). Mars meteorites are known on Earth. Today the surface of Mars is a freeze-dried desert; any extant life would probably lie deep underground. I am investigating the plausibility of the above scenario, and seeking additional evidence to support the "Mars first" hypothesis. This subject forms the central theme of my book The Fifth Miracle / The Origin of Life.
Nature of Life
Definitions of life are notoriously contentious. I am developing a new line of attack based on the notion of life as an information processing and replicating system, i.e. stressing the software over the hardware aspects. This entails trying to understand how information processing and autonomy system can emerged in an uniformed system.
Origin of Life
This is the Big Problem, and one of the outstanding challenges to science. I have a hunch that quantum physics played a role in this transition, and I'm investigating a number of mathematical models to determine if and when quantum mechanics can play a non-trivial role. I am also using computer models of cellular automata with novel types of dynamics to try to capture the elusive notion of emergent complexity in a rigorous way.
Are We Alone? The Search for Life in the Universe
So far, there is no direct scientific evidence for any life beyond Earth. The possibility that life might be widespread in the universe hinges on how easy it is to emerge from non-life - the big unknown discussed in the foregoing section. For my own thinking, see Wild ideas I like to think about.
Our perception of time in daily life is seriously at odds with the physicist's concept of time. For a start, we experience a flow of time. The universe possesses a pervasive arrow of time, or time asymmetry that can be traced back to the cosmological initial conditions, but this makes no reference to a flow. The other problem is that time's arrow is associated with our imperfect, macroscopic notion of the world, i.e. it is derived from coarse-graining. But how can something as fundamentally important as time's arrow, with its link to the second law of thermodynamics, rest on an essentially subjective criterion?
The Laws of Physics and Emergence
The status of the laws of physics - what are they and where do they come from? - is an old philosophical problem that has received a new twist with modern scientific ideas like string theory and the multiverse. I am developing a new slant on this problem by investigating whether the laws of physics might be emergent, rather than absolute, universal and Platonic. (See my paper for more about this topic). I have suggested a link between the way the laws of physics operate and the large scale properties of the universe. This opens the way to the possibility of hitherto unknown "higher level" emergent laws, such as biological principles of organization, that are consistent with, but not reducible to, the traditional laws of physics. In connection with this project, I am trying to sharpen the concept of "downward causation", where wholes have causal efficacy over parts. I am also seeking to eliminate the age-old dualism between absolute unchanging laws of physics and time-dependant contingent states of the world, and develop a notion where laws and states might co-evolve.
Quantum Mechanics and Reality
I have a longstanding interest in the emergence of classical reality from the underlying quantum world. My personal conjecture is that classicality is an emergent phenomenon associated with the complexity of a physical system. This puts me at odds with most of my colleagues. I am investigating whether cosmologically-emergent physical laws might provide a way to test this idea.
The oldest problem of philosophy is the nature of consciousness. I take a pragmatic view: consciousness exists, therefore we need to explain it scientifically. As a physicist I would like to know: (i) When is a physical system conscious? Is it a matter of complexity, the right stuff or what? (ii) How can a physical process, like swirling electrical patterns in my brain, create sensations, thoughts, images, etc.?, and (iii) How can thoughts, desires, intentions, move matter, as when I will my arm to rise? At present, I haven't a clue about any of these three posers, but I'm thinking about it.
One of the most contentious issues in fundamental physics and cosmology concerns the role of the observer. Thirty years ago Brandon Carter formulated the badly-named "anthropic principle" - that the universe necessarily contains the laws and conditions for life and observers to exist. This principle has some force if it can be demonstrated that the existence of life is highly sensitive to the precise form of the laws or cosmological initial conditions. Many scientists believe that is the case, but testing the anthropic principle isn't easy. It receives its most comprehensive treatment in connection with the multiverse. I am working on some mathematical models of the laws of physics to test the sensitivity of life to changes in the fundamental parameters of the models.
Why is Nature Mathematical?
Theoretical physics proceeds from the basis that the laws of physics are mathematical. But why should that be the case? Mathematics is, after all, a product of the human intellect, so its extreme success in describing realms such as subatomic particles or cosmology is a mystery. I believe this issue is connected to the wider problems of the nature of physical law, the emergence of life, and teleology. These are as yet only vaguely formulated ideas I am trying to sharpen.
By teleology, philosophers refer to some sort of final causes or goals or evolutionary directionality in the universe. Teleology was more or less eliminated from science following Darwin 's lead, but a residue of teleological thinking may yet have explanatory value - at least I am prepared to consider that it might. I have been developing a set of notions I call "teleology without teleology." I am searching for some sort of law of increasing complexity (i.e. a principle that the universe has a trend towards greater richness and organizational diversity), or seeing whether states that are in some sense computationally deep (e.g. life) might emerge favourably as attractors in the space of states. This might have application to the origin of life, and possibly the origin of consciousness. A preliminary skirmish with these notions can be found in my book The Cosmic Blueprint.
What is Information?
Information is playing an increasingly fundamental role in science. It crops up in very different contexts in thermodynamics (in relation to entropy), quantum mechanics (the wave function represents our knowledge of a physical system), in relativity theory (information cannot travel faster than light) and in biology (a gene is a set of instructions). I am attempting to understand how the concept of semantic, or meaningful, information, represented for example by the genetic code, can emerge from "meaningless" information of standard thermodynamics, and whether information is a deeper-level concept that matter and law. This takes inspiration from John Wheeler's "It from bit" dictum.
Ultimate Reality and God
Can science ever provide a complete and final explanation of the physical universe? If not, what is left out? Topics like ultimate reality and ultimate explanation occupy a lot of my attention, and inevitably overlap with questions about God, purpose and teleology. The thorny topic of God I discuss in myTempleton Prize address. See also my books God and the New Physics and The Mind of God.
The measurement of time in quantum mechanics is problematic. I am investigating the use of specific models of quantum clocks to obtain unambiguous answers to questions such as how long a particle takes to tunnel through a barrier and the time required for particles to fall in a gravitational field. These topics relate to the question of the conceptual consistency of quantum mechanics and relativity. Quantum clocks might also play a role in biological systems.
The application of quantum field theory to black holes shows that their horizons are a measure of entropy. This idea may be generalized to cosmological horizons for a number of expanding universe problems. I am generalizing the second law of thermodynamics to cosmological horizons as a means to place constraints on cosmological models, and to investigate the status of the so-called holographic principle.
Many cosmologists believe that the universe we observe is an infinitesimal component of a "multiverse," or ensemble of universes, with differing properties and laws. I am developing some new ideas for testing this hypothesis.