**Warning: Crazy talk ahead.** Some of you may remember that I wrote about inflation and why its alternatives fail awhile back. Apparently, Louise Riofrio didn’t get the memo. When there’s misinformation about cosmology out there, it’s up to me to set the record straight. (And I am not alone.) Let me first remind you about one of the alternatives to inflation I debunked last month:

Add defects and vary the Speed of Light.This one’s out. Why? Because we would see defects in the Cosmic Microwave Background, and we don’t. The constancy of the speed of light is highly supported by experiments, but there is a theoretical disaster if it turns out that either c (the speed of light), G (the Gravitational constant), or h (Planck’s constant) changes: energy is no longer conserved in the Universe! It’s possible, but… yeesh!

Now, it is very important to consider alternatives to our cosmological model, and to test them as best as possible, both experimentally and observationally, as well as theoretically for consistency.

So let’s remember what inflation does for us: gives us a flat Universe, with the same temperature everywhere, without defects or ultra-high-mass relic particles, and the observed spectrum of fluctuations. Well, Louise comes out with this graph, which I assume comes from a popular science magazine:

Now, I’m not an expert on inflation, but I’m pretty adept with it. Inflation does *not* give a unique prediction like that for the angular correlation function. Each individual model of inflation does, but we don’t know what that model is. How do we figure it out? Measure the scalar and tensor indices, as well as other cosmological parameters, and then reconstruct the model of inflation from that. What’s Louise’s solution? Vary the speed of light and change the age of the Sun, Earth, and Universe. That could be why her work isn’t published in peer-reviewed scientific journals.

There is crazy out there, folks. Even from people with Ph.D. degrees, sadly. Does inflation solve everything? No. But is the speed of light constant? Well, we can place limits on its variation from two major sources:

**1. Quasar Absorption Lines**: These can be used to measure the time variation in the speed of light, as the frequency of the absorbers are highly dependent on whether the speed of light stays the same or not. (For those of you who are experts, this is the same experiment that measures variations in the fine-structure constant.) The results for this place limits on the variation of the speed of light, c, to change by less than 0.24% over the last 10-12 billion years. (Remember, if you will, that the Universe is only 13.7 billion years old.)

**2. Natural Nuclear Reactors**: the Oklo Nuclear Reactors have been going strong for nearly 2 billion years. By measuring the rate of radioactive decay and isotope abundances, we can determine how much the fine structure constant, and therefore how much the speed of light, has changed. The limits from this are that over the last 1.7 billion years, the speed of light has changed, at most, by 0.02%.

Now what is Louise’s prediction? That the speed of light, c, changes as the age of the universe to the minus-one-third power (i.e., c ~ t^{-1/3}). Over the same time as Oklo (where t changes from 12.0 billion years to 13.7 billion years), that would correspond to a change in the speed of light of 4.5%, or *over 200 times what is observed*.

Verdict? Inflation, valid. This alternative? Invalid. Very, very invalid. And don’t let anyone, even the Carnival of Space (which I love, is great this week, and you should check out), tell you different. You’ve got the info, now, and you know better.