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Comment by n4r9 | Hacker News Reader

I agree that most physicists believe that an external reality exists.

I agree that physical theories aim to describe how it works.

But I disagree that it follows that our physical reality has a mathematical structure. My objections are:

- There is no compelling reason to think that "purely abstract" mathematics any less anthropocentric than human language;

- Even if mathematics transcends humanity, there is no compelling reason to think that there is a single overarching mathematical structure of the universe, despite being able to predict the outcomes of our interactions to greater and greater accuracy as our physical theories develop.

It may be that Tegmark addresses these points in his "full strength" version, but given the way he glosses over these hidden assumptions in this paper, I'm not inclined to dig in and find out.

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Tegmark believes (pardon me if I have this wrong) that all conceivable realities exist that can be described by equations, not only this reality. The reality we have access to is the one in whose equations we are ourselves locked up, so to speak.

I'm basically with Tegmark. For one thing, what has physics ever come up with but equations, and improved equations to replace those, and so on? Everything so far has been math.

So, going forward, either everything in physics will always be rooted in math, or else some "non-math stuff" has to be discovered. (The very idea of "non math stuff" being at the root of reality seems absurd.) What kind of thing would that be? I think if we discover the ultimate equations then that's all there will be: those equations, and mysterious constants embedded in them that just are. The only explanation for those constants will be the anthropic principle: if those constants were different, we wouldn't be here to contemplate why they are, and in some other universe there are beings completely different from us also wondering why their constants and equations are they way they are.)

For reference, the poorly named "standard model" which is the quantum theory of all forces except gravity, cannot really be called equations in the usual sense. This is because the kind of mathematical model that would describe the standard model (nonperturbative QFT) can't currently be done rigorously. It can only be done for simpler models in lower dimensions. The standard model is a very complex sort of approximation to a theory that is assumed to exist.

This might be a mere detail to some but to me it is a sign that physics is complex in all kinds of ways, and can't really be described as "choosing the right equations". Even if you think that this is what physics is fundamentally, I think you would have to admit that it wasn't possible to describe what the meaning of "equation" was before qft was developed, and the same may be true about future theories that unify the standard model and gravity.

I don't think this really addresses my objections. The fact that physics is described mathematically could be an artefact of how mathematics is the most "agreeable" way for humans to come to a consensus. It seems to me inescapable that mathematics is inherently anthropocentric.

I think this is a false dichotomy:

> ...either everything in physics will always be rooted in math, or else some "non-math stuff" has to be discovered.

I can imagine a plethora of other possibilities. For example, there may be nothing "at the root " of reality, no ultimate equations. We might get better and better at predicting and manipulating the universe around us, but never close down on some ultimate truth.

> For one thing, what has physics ever come up with but equations, and improved equations to replace those, and so on?

Observations of nature and rational explanation of those in terms of old but also new concepts. Equations are just one of technical artifacts to help us think in a precise way. If we had computers sooner, there might have been physics without differential equations.

What observations are made in physics experiments which don't end up expressed as a cluster of floating-point numbers?

I think you're missing my point. Physics did not give us merely equations, it is also gave us concepts such as force, temperature, energy and physical principles such as principle of conservation of energy, principle of relativity etc. (Floating-point number is a concept referring to implementation of rational numbers in computer engineering. I do not think it is relevant here.)

I think the previous comment was getting at concepts like "the laws of physics are the same in all inertial reference frames". It doesn't directly refer to any mathematics, although of course it can only be tested via the quantitative predictions that follow from it.

I understand the statement "the laws of physics are the same in all inertial reference frames" as referring to correspondences and invariances among some math under a coordinate transformation.

Tegmark is explicit about his assumptions elsewhere. For an overview, see https://en.wikipedia.org/wiki/Mathematical_universe_hypothes....

Indeed, it's not the only productive line of thinking in physics.

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