Smolin on “The Problem of Time”
The first lecture by Lee Smolin on “The Problem of Time in Quantum Gravity and Cosmology” is available from the new PIRSA site.
Edit: Ah, glad to see a mention of Bergson in the scheduled lecture of March 19, “History of the problem of time”. But there is no mention of Saint Augustine.
Update – Here are the presently available presentation files:
Lecture 1.
Lecture 2A.
Lecture 2B.
Update Jan 25 2008:
Update Jan 31 2008:
Lecture 4.
Lecture 4B. (appears to have been removed).
Update Feb 9 2008:
Update Feb 14 2008:
Update Feb 20 2008:
Update Mar 06 2008:
Update Mar 20 2008:
Lecture 8.
Lecture 8B.
Lecture 9.
Lecture 9B.
Update Mar 31 2008:
January 16, 2008 at 4:56 am
He’s an excellent lecturer!
January 17, 2008 at 11:18 am
What is time? Here are my propositions. As I see it, there are only 2 possibilities:
A- Time is movement.
B- Time is related to movement.
Accordingly, what would be the ontological status of time?
A’ – If A, time is necessarily an emergent phenomenon.
B’ – If B, time can be either an emergent (B1) or not an emergent (B2)phenomenon (namely, it is fundamental).
What is the ontological structure of time?
A” – If A, time is necessarily a mathematical structure.
B” – If B, time can be a mathematical structure in case B1, and it can be, in case B2, an independent entity, to which is possible to find a mathematical function able to describe “effects of movements” on other entities, but which is itself, a “nonvolatile”, permanent entity, non-mathematically describable (not a number, not a function, not an equation, etc).
Proposition: Time and inertia are intertwined entities.
To address the question of whether time exists in the first place, I believe that you would have to address the nature of inertia. Since after a moment’s thought there are only 2 possibilities for defining time: A- Time is movement. B- Time is related to movement; considering that inertia is the most “intrinsic” movement one can imagine, I strongly believe that time and inertia are intertwined entities.
The following is just a simple thought experiment that undoubtedly deserves more elaboration, but from it you’ll see what I am at.
Suppose an universe in which there exists only one spinning body or particle, which cannot access information from outside an isotropic/uniform box to which it is confined.
If inertia were a property that depended on the existence of other particles in the universe, ie, if it were not an intrinsic property of the body, the spinning particle, being completely alone in the universe, could not tell that it is spinning, and as a consequence it could not tell by any means that time exists (ie, passes). Even if the universe by itself evolved in such a way (or had some property) that could change the spin rate of the particle, the particle could not “tell” it, since it would not bulge, given that the universe was empty except for the existence of that particle, and in this case it is assumed that inertia depended on the mutual existence of other particles. If you included more and more other particles in the universe, however, the original body would bulge, and the degree of the bulge could change, e.g., by the change of the configuration of the other particles. That change would measure time.
On the other hand, if inertia were an intrinsic property of the body (did not depend on other particles in the universe, but only on the particle itself), the alone-particle-in-the-universe could in principle tell that time exists, but in order to tell it, its spinning rate would have to change, in order that its bulge changes, and that would indicate the passage of time. That would presume some property of the universe that acts as an effective torque on the particle as the universe evolves. It would then bulge, even if it were the only particle in the universe, and time would pass.
These are of course unrealistic or too simple thought experiments, but I believe there is some deep connection involving time and inertia (and both in a large-scale sense involving the nature of the universe itself). There is also, of course, quantum mechanical issues one could argue about (or even quantum gravity issues, for that matter, also involving thermodynamical issues)… Time is a great mystery.
The division between “past”, “now” and “future” is, IMHO, a human trait, which nonetheless embeds the whole construction of our theories and how we make measurements to confirm them. Whenever we move farther and farther from our common sense experiences more and more that division of time (“past-now-future”) becomes more and more peculiar. This is an indication that nature’s substratum might operate in a different manner.
Christine
January 17, 2008 at 11:26 am
My previous comment is of course a very simplistic one. I consider it just some sort of initial exercise. And of course there is a lot to be exercised… There is the statistical mechanics problem (arrow of time, etc). And many other issues. In my opinion, the notion of time is the most difficult problem to address, and I believe, like many other people, that in order to have a theory of quantum gravity, a conciliantion of the notion of time in quantum mechanics and general relativity will be required. And cosmological issues have key points in that respect as well.
Christine