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In your articles you defend the recently proposed theory that gravity is an entropic force, driven by the increase in information. Based on that, what would be the fundamental constituents of the Universe?
Gravity can be understood as an entropic force, provided our universe is holographic in nature. And for that to be the case, the fundamental degrees of freedom need to be much sparser than one might expect based on standard quantum field theory. These holographic degrees of freedom are manifest in space-time in the form of causal influences. In loose terms one can think of these as discrete ray paths which fill space-time due to their direction being somewhat uncertain.
What exactly is your view on space-time? You seem to think it is discrete rather than continuous?
Space-time is emergent in a way we do not understand. Some causal structure must be the foundation from which space-time emerges. I am convinced this causal structure is discrete in nature. It has to be for the emergent space-time to have holographic properties.
In one of your articles you defend the possibility of a theory of everything. Does that imply the possibility of truth? I. e. of knowing something for a fact about the Universe?
Hawking and many others have claimed that Gödel’s undecidability theorems prevent a theory of everything. That is a wrong conclusion. Gödel does not prevent us to construct a theory of everything, but he does prevent us to turn this theory into a crystal ball. If we have a theory of everything, we will still not be able to predict the outcome of a coin flip, let alone predict tomorrow in all its details. So a theory of everything is possible, but it is a misnomer.
Now what does such a theory imply in terms of truth? Truth in this context is nothing more than the recognition of a consistent description that correctly describes measurement outcomes. So yes, I guess we will know truth – in an operational way – when we have a theory of everything.
What is your take on the Stephen Hawking-God issue?
An absolute non-issue. An old message really. With the gravitational energy of the universe balancing the mass-energy content, the total energy of the universe adds up to zero. So, energy-wise, the universe can emerge out of nothing, and quantum physics tells us that what can happen, will have a finite probability amplitude of happening. That’s all there is to it. Hawking’s publisher has made a clever marketing move by playing the god card. Yet, from a physics perspective the whole claim ‘god not needed’ is empty.
Being a physicist, you’ve learned the deterministic (albeit chaotic) theory of Newton, then jumped to the probabilistic (when making a measurement) Quantum Mechanics. Do you think free will is compatible with either of those world-views? Or is it just an illusion of our minds?
We have no clue whatsoever what is free will and how it emerges. What we do know is that our physical theories are deterministic, but that does not mean these leave no room for free will. Key concept in this is Turing’s idea of uncomputability. Newcomb’s paradox disappears and free will gets free reign when we take uncomputability into account. In this context it is important to realize that gravity profoundly deepens Turing’s concept of uncomputability. Gravity limits the size of the computation that can be accommodated in our universe. The universe itself is the ultimate computation, any larger computation will disappear behind causal horizons. So there is no way to predict what will happen other than to create a universe to make it happen. That concept leaves a lot of room for unpredictability, free will if you like.
However, all of this doesn’t tell us why you and I seem to have this thing we call free will and a stone apparently not. When it comes to issues like free will and consciousness, physics simply has no answers.
Lately -over the last 50 years- the world has seen the rise of currents of thought such as constructivism, still very popular in social science circles, which place their emphasis in questioning the role and explanatory power of science. Similarly, disciplines like homeopathy are starting to be taught in universities and funded by governments, despite their repeated failure to show any real results. Nowadays, it is becoming increasingly popular to say things like “everything is relative” or “there is no truth”. Why do you think this is happening? What can scientists do to reverse this trend?
I noticed on my weblog that articles that carry titles that may be interpreted as critical towards science attract hugely more readers than other articles. In bookshops the shelves labeled ‘metaphysics’ extend far beyond those labeled ‘physics’. It seems fashionable to question scientific results and to deny science its power to brush aside and eliminate irrational fantasies.
On the other hand, has this ever been different? These days irrationality has a strong voice, particularly so on the Internet. But that does not mean irrationality is increasing. I am an optimist at heart, and would like to believe that science awareness and interest in science, if anything, are increasing. But things you do not understand can come across as threatening. And there is undeniably a wide gap in science understanding. There is a clear task for scientists to communicate with an audience far wider than fellow specialists. That is not easy, but it must be done. There is a huge appetite for science blogs. I am happy to play an active role in this area, and I hope more scientists will liberate time to do so. Also, science needs to become more open, and results funded by tax payers need to become fully public. Sites like Arxiv are a blessing, but still too many articles are not freely available.
Finally and on a lighter note, what is the meaning of life?
To live it to the fullest.