In the piece, the author includes this quote by Sean Carroll:
“Whether or not we can observe [extra dimensions or other universes] directly, the entities involved in these theories are either real or they are not. Refusing to contemplate their possible existence on the grounds of some a priori principle, even though they might play a crucial role in how the world works, is as non-scientific as it gets.”
and sums it up as this:
Thus, for Carroll, even if a theory predicts entities that can’t be directly observed, if there are indirect consequences of their existence we can confirm, then those theories (and those entities) must be included in our considerations.
I have several problems with this:
- We can’t really “confirm” anything in the sense that we can show it to be true. We can show that our measurements are consistent with theoretical predictions.
- Referring to direct and indirect observations without defining them makes that a meaningless statement. To be fair, Sean Carroll mentions direct observations and the author uses similar language. What would it even mean to directly observe something? In HEP we identify particles by their effects on the materials in our detectors. We can’t just grab a particle and ask it what it is. For particles that decay quickly, such as the W and Z bosons, we can only infer their existence from a statistical analysis of data. We can’t look at an event and say that it includes a Z. We can only say that it is consistent with a Z. Furthermore, particles like gluons and quarks are even more complicated to find, but we still accept their existence.
- After reading the linked essay by Carroll, I don’t think that’s a great quote to use to talk about his position. In the case of string theory, he mentions that string theories (i.e. the specific theories allowed in the general string theory framework) can make very specific predictions, most of which are inaccessible due to technological limits. String theories are in principle falsifiable. The multiverse is not necessarily falsifiable, but according to Carroll does make real predictions that can inform our understanding of the universe (and our empirical data). I think the point on string theory is not very controversial, but the point on the multiverse (i.e. the multiverse doesn’t need to be falsifiable to be scientific because it can affect how we interpret our data) probably is.
Anyway, after writing this and rereading the previous post, I definitely get the feeling that the NPR blog post isn’t giving a great explanation of what this debate is actually about. It’s summarizing things too much and losing a lot of the nuance in everyone’s positions.