More on the string thing

Leonard Susskind, “the” Professor of Theoretical Physics at Stanford University in California, is interviewed by New Scientist on the demise of String Theory. Some startling quotes:

The mathematics are rickety, but that's what inflation implies: a huge universe with patches that are very different from one another. The bottom line is that we no longer have any good reason to believe that our tiny patch of universe is representative of the whole thing.

...where “our tiny patch” is billions of light-years across...

What finally convinced you?

The discovery in string theory of this large landscape of solutions, of different vacuums, which describe very different physical environments, tipped the scales for me. At first, string theorists thought there were about a million solutions. Thinking about Weinberg’s argument and about the non-zero cosmological constant, I used to go around asking my mathematician friends: are you sure it’s only a million? They all assured me it was the best bet.

But a million is not enough for anthropic explanations — the chances of one of the universes being suitable for life are still too small. When Joe Polchinski and Raphael Bousso wrote their paper in 2000 that revealed there are more like 10⁵⁰⁰ vacuums in string theory, that to me was the tipping point.

...then we start getting seriously metaphysical...

The great hope was that some deep mathematical principle would determine all the constants of nature, like Newton’s constant. But it seems increasingly likely that the constants of nature are more like the temperature of the Earth — properties of our local environment that vary from place to place. Like the temperature, many of the constants have to be just so if intelligent life is to exist. So we live where life is possible.

...then get an interesting definition [bracketed comments in the original]...

There is a philosophical objection called Popperism that people raise against the landscape idea. Popperism [after the philosopher Karl Popper] is the assertion that a scientific hypothesis has to be falsifiable, otherwise it’s just metaphysics. Other worlds, alternative universes, things we can’t see because they are beyond horizons, are in principle unfalsifiable and therefore metaphysical — that’s the objection. But the belief that the universe beyond our causal horizon is homogeneous is just as speculative and just as susceptible to the Popperazzi.

...and he finishes with this guaranteed gold-plated argument-starter:

If we do not accept the landscape idea are we stuck with intelligent design?

I doubt that physicists will see it that way. If, for some unforeseen reason, the landscape turns out to be inconsistent — maybe for mathematical reasons, or because it disagrees with observation — I am pretty sure that physicists will go on searching for natural explanations of the world. But I have to say that if that happens, as things stand now we will be in a very awkward position. Without any explanation of nature’s fine-tunings we will be hard pressed to answer the ID critics. One might argue that the hope that a mathematically unique solution will emerge is as faith-based as ID.

No wonder some quite intelligent people regard String Theory as confusing and frightening. Worse than Hawking and his random objects materialising near a singularity.