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Comment by lidHanteyk | Hacker News Reader

Modern physics assumes symmetry and then searches for models which fit observations under the constraint of symmetry. However, we are starting to wonder whether the symmetries truly exist. Time, charge, parity, position, momentum; we hope that they have symmetries.

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That doesn't sound like a fair description. Physics doesn't simply assume symmetries exist. We've observed symmetries that hold up under all observational and experimental scenarios available to us. From that, it's quite reasonable to consider the possibility that those symmetries are truly universal, and to study models that treat those symmetries as universal. Those models have great predictive power for ordinary scenarios of the sort where we know from experience that the symmetries do hold up, and those models tend to be simpler than ones that break symmetry in exotic scenarios. When we actually find a broken symmetry (eg. space, time and momentum behaving oddly at speeds close to c), it's time to update those models, which then usually reveals a more subtle symmetry and conservation law.

But there's no big trend in physics that casts doubts on all the important symmetries in physics. Even under as-yet undiscovered theories, the symmetries we're familiar with will always remain true in the limit as the conditions approach familiar everyday circumstances. Nobody is worried that concepts like time, charge, momentum, etc. will be discovered to be a silly, unfounded idea that the universe casually disregards. We're just not adding extra terms to the equations until there's a need for them.

> Nobody is worried that concepts like time, charge, momentum, etc. will be discovered to be a silly, unfounded idea

While not overly worried, I have to confess that I'm at least somewhat worried. And somewhat convinced that our present conceptions of theses things will one "day" be turned on their head, in a way that might also seriously affect our everyday conceptions of them.

I would support adding a couple of properties to most if not all our established models; notably 1: known unknowns, and 2: unknown unknowns. It would seem a healthy antidote to the hubris that runs rampant among scientists, at least before they discover the ubiquity of these two properties (they usually do around the 50 year mark).

This is word salad in a math-heavy field.

I second this. Conserved quantities (by extension symmetries) do not compute. Car engines and refrigerators are both thermal engines, but the same conserved quantities are engineered (say programmed) to do different things.

What does it mean to "wonder whether the symmetries truly exist"?

Isn't that a question to be answered by experiment?

Perhaps "truly" also in the sense of to what precision. To the precision of measurement in experiments is usually fine :) When the theory is not measurable anymore, than it's questionable whether it's Physics or already Meta-Physics...

Is the universe expanding? How could you tell? The attempt to answer these questions has tripped up everybody since Hubble and Einstein.

Hum, the universe is both predicted and observed to expand.

> Hum, the universe is both predicted and observed to expand.

Or the universe may not be expanding and time could be contracting.

What does “time contracting” mean?

While I understand the similarity to what BoiledCabbage is saying to whackjob theories, BoiledCabbage is actually referencing real physics discussions that have occured in the past. Specifically, there is the problem of measuring the universe when you don't have anything not in the universe itself to do the measuring with. What if, for instance, the three dimensions aren't all the same size as it seems, but actually, x is five times larger than y or z and everything time things rotate, including all of your measurement apparatus, they actually grow and shrink? How would you detect such a thing? What if as you look out into the universe, all the constants actually shift in a way that time ends up running at a different speed, so instead of an expanding universe and light taking a long time to get to us, instead there is some sense in which the external universe "really is" younger, and the reason we witness ourselves in a bubble of old universe is simply the anthropic principle?

These were all very serious questions around the time of relativity being nailed down, especially since one of the implications of relativity is precisely that you don't have any absolute rulers anymore. While overall the scientific consensus is the scientific consensus, the problem still remains to a lesser degree even today. There's a recent paper questioning whether or not the universe's acceleration rate is actually expanding, because they posit a systematic error in our understanding of the standard candle supernovas used to measure it. What if the "standard candle" turns out to be more dependent on the chemical makeup of the stars than was previously understood, which as the universe gets older the stars have more non-hydrogen in them, so as you look to the younger parts of the universe you misjudge how far away they are systematically? Your ruler was bent in a way you didn't realize, so the distances don't work, so it looks like the universe's expansion has been expanding and there must be this "dark energy" that ends up making the majority of the universe, when it could just be a chimera of our inability to reference absolute measurements.

If you find a symmetry violation, you'll probably get a nobel prize. Best of luck.

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