A Funny Thing about Rainbows

In this month in which the symbol of the rainbow has been appropriated by, shall we say, non-traditional causes, it might be good to look at rainbows as they actually are and what they actually mean.

Rainbows are a reflection phenomenon created by dispersion. Dispersion means different frequencies of light are bent different amounts in the medium (in this case usually rain) through which the light travels. So the colors that make up the white light are separated out in the various bands that make up the rainbow.

The thing I'd really like you to notice about rainbows here is how to notice them. They usually appear when the sun is low in the sky (for example, not long after sunrise or not long before sunset) and when it's raining in the part of the sky 180 degrees away from the sun. So if it's later in the day, not many hours before sunset (i.e., sun in the west) and raining in the east, you'll see the rainbow in the east.

What this means is that rainbows usually appear in the midst of rain, or near rain. The most dramatic rainbows have a dark, stormy backdrop.

There's a moral to be had from this coincidence of rainbows and dark sky. If the rainbow appears behind you, you're leaving a stormy past. You survived. If the rainbow appears in front of you, the rainbow reminds you that the storms you're about to enter will not last forever. There is hope.

Rainbows are symbols of hope.

Apologies to Maudlin

In my last post I complained about the philosophers George Ellis recommended in Sabine Hossenfelder's book. Further research reveals that I was wrong. I have to retract my complaint, at least in the case of Tim Maudlin. I'm happy to report that Maudlin appears to have a healthy respect for Aristotle. Further, the latter part of his paper on substances and space-time is written in the style of Thomas Aquinas's replies to objections in the Summa.

Maudlin also has a very good paper on unification in physics from which I think Hossenfelder and Smolin would profit. He asks what unification means and sets out some limitations of what we can reasonably expect from unification efforts.

A young theorist friend of mine points out that people largely aren't working on grand unification schemes these days (viz., GUTs, TOEs) and that the figures interviewed in Hossenfelder's book who are working on unification are either older or somewhat marginal. (Admittedly he wasn't familiar with some of the names.) It strikes me that the people who are most concerned with unification are people like Hossenfelder and Smolin who write books on what's wrong with unification efforts. But what they really need to consider is that the possibility that unification of physics isn't possible within physics as we understand it today, but through philosophy, that is, natural philosophy (in other words, by also bringing in some methodologies more typically characteristic of metaphysics). (I wonder if Ellis was hinting in that direction.)

Discovering truth is unification, at very least bringing together reality and the mind, but also often finding commonalities in previously separate insights. The over-all tendency of a truth-discovering activity like philosophy is to unify seemingly unrelated parts of and thoughts about the universe.

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Tim Maudlin 1990 "Substances and Space-time: What Aristotle Would Have Said to Einstein," Studies in the History and Philosophy of Science 21:4, 531-561.

Tim Maudlin 1996 "On the Unification of Physics," The Journal of Philosophy, 129-144.

Sabine Hossenfelder, Lost in Math: How Beauty Leads Physics Astray (New York: Basic Books, 2018).