Thursday, October 8, 2009

Andrei Linde On Inflation

I have already quoted Alan Guth, often considered as the founding father of inflationary physics, as claiming inflation implies an eternal multiverse.  However, every cosmologist who cites Guth as proposing inflation will then immediately cite Andrei Linde.  This is because Linde's contribution to the initial inflationary models were just as important as Guth's.

This is what Linde says about the eternal nature of inflation, after doing a bunch of calculations, in his 2007 paper which has already been cited over 100 times:
The universe enters eternal process of self-reproduction. The existence of this process implies that the universe will never disappear as a whole. Some of its parts may collapse, the life in our part of the universe may perish, but there always will be some other parts of the universe where life will appear again and again, in all of its possible forms.
As I mentioned before in the above Guth post, inflation implying an eternal multiverse is just as real of a prediction that the universe is flat, produces distinct peaks observed in the power spectrum, produced scale-invariant curvature perturbations, made those perturbations Gaussian, produced a spectral index slightly less then one, and every other prediction we have verified.

I don't think it is fair to a physical theory, after seeing every other prediction is verified with flying colors, to reject the rest of the predictions as philosophy just because they may be out of our realm of detection.

This eternal multiverse coming from inflation is probably just as real as all the rest and I think people need to take that seriously.

Now, in fairness, Linde next says this:
One should be careful, however, with the interpretation of these results. There is still an ongoing debate of whether eternal inflation is eternal only in the future or also in the past.
I agree, we must be careful. I think it is very possible to read too much into all this. However, I still maintain this is more than just philosophy given that it is rooted in an underlying physical theory that on so many levels has been experimentally verified. (Admittedly, there are a few more predictions to go.)


  1. I think there is a real misunderstanding of what real philosophy is, because it is not normally under theoretical sciences, but this sciences are part of it as we can see for Descartes or Leibniz who did find E= m.v². And it is important to not make a confusion between a great philosopher who is enough general to have a real doctrine (including theory in sciences) and the cheaters who are not even philosophers but want to have this distinction.

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  3. PhD is in order to be Doctor of Philosophy, and I should precise in a part of philosophy because it is not obvious that one is a philosopher with such a degree.

  4. Cartesian,

    You are right, and it is important you brought it up. PhDs are ultimately an indication you are a Doctor of Philosophy. Scientific theories are technically as much philosophy as anything else.

    I guess sometimes people play a semantics game and label philosophy as something that can only be argued rationally, not that you can actually do some sort of concrete test. They then label science as something that can both be argued rationally but also tested in some concrete physical way.

    But this is only semantics. Technically science is a form of philosophy and so I concede you bring up a good point.

  5. Joe,
    I've said it before, but the problem I have with extrapolating to an eternal multiverse from inflation is that inflation itself relies on some totally unknown force. Anytime one has to invent a new force to make one's theory work, it will make everybody else pretty nervous about that theory and even more so about extrapolating new theories from it.

    I should mention that this goes for dark energy and dark matter as well - since we don't know what they are, it's pretty tough to anticipate any surprises they might throw our way.

  6. Nick, you have a fair point, but my defense is that inflation was not just being altered to fit the data. It made predictions about things we didn't know at the time that turned out to be correct. It was and is predictive, not just changing to fit data.

    But, your point I believe is specifically: we don't know the mechanism that drives inflation. This is true and I freely admit that. I also will admit there are some testable predictions it makes that are yet to be verified. (Hence the Planck satellite, etc...)

    However, and this is also important: every known mechanism that could possible produce a superluminal expansion of the universe throws the universe into an eternal inflation scenario. My point is regardless of the mechanism it appears this may happen.

    However, to be fair to Nick and the public in general: we don't know the mechanism and there are still a few testable predictions to go.

    I feel like a cosmologist at the time of the discovery of the CMB where I see what I feel is some real bullet proof evidence for inflation but the theory is admittedly on shaky enough ground that the public deserves to be skeptical.


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