That said of course whatever quantum gravity would bring it'll need to reduce to match known physics. However at the fringes of known physics what will happen as you get nearer to the singularities in special relativity? Generally speaking in the past singularities in physics have been due to incomplete knowledge of the physics in these regions.

- We have not found any evidence for it.

- Some predictions have been made from it that weren't found (e.g. no supersymmetric particles in the LHC).

- It can be tuned to fit almost fit any universe and any observation, which doesn't really make it scientific.

- The reasons for inventing it might have been misguided or flawed. (universe must be beautiful / simple / etc).

The lack of results are turning a growing part of the scientific community off, while there is still a core amount of scientists holding on to it.

What would be your estimate of disagreement with her other takes?

Personally my biggest question would be why didn't we observe anything FTL in the Universe yet. But it could be, just like with many scientific discoveries, what has been a great data point has been dismissed as some measurement problem.

What is at stake is "Some scientists should consider FTL travel possible, and give it a go." for such a statement, the argument definitely holds water.

If something was FTL, and we need light to see things, how could anything FTL be seen, as light could not move fast enough to reach it then reach our eyes. Further, assuming we could travel FTL, while traveling we'd be nearly blind, and anything we did see wouldn't make any sense.

Basically you'd see the same thing from multiple locations, as the light emitted closest to you will hit you at the same time light emitted in the past from further away reaches you. It would construct as two objects going in opposite directions.

Just because something is moving faster than the speed of light doesn't mean the light reflected from it never reaches our eyes.

I think another way to perceive it is as if you have a buffer that is beginning to overflow because you can't empty it faster than the speed of light. That overflow is how I'd imagine you'd detect FTL objects. It's like the visual equivalent of a sonic boom. Again idk what I'm talking about, but it was nice to think about :)

We have observed at least one FTL phenomenon -- sort of. We know entangled particles communicate with each other FTL because of the Bell inequality. We just don't have any influence on what message they communicate (and we probably never will).

This could be the case in reality. But its utterly useless information, because it doesn't really give you a direction in which you can even begin to investigate it. Saying that something is possible in this regard is saying that our knowledge of our reality has holes, and "anything" can be in those holes, nothing about the specifics of what could be in those holes.

One of SH's hobbyhorses is that the Universe has no obligation to conform to the most elegant symmetrical theory. (See C/P/T symmetries.)

I enjoyed her talk. She pointed out the subtle flaws in the commonly held view that the speed of light is an absolute limit.

At no point does she say this means it is not a limit, only that this conclusion is not fully warranted from the theory we have now, which we also know to be incomplete.

That isn't to say that Hossenfelder's bold prediction is necessarily true. But that by double-checking the rudiments themselves, we might find _better_ rudiments.

Consider the axiom of choice. We know it can't be constructed from ZF alone, and so we just throw it in sometimes. But - ZF's axioms are constructed for practical purposes as well. While they are taken as basic principles, they have been carefully studied and analyzed to avoid inconsistencies and paradoxes. The axioms provide a stable foundation for set theory that has effectively served as the groundwork for modern mathematics. But that is a construct made from necessity for rigor - not necessity for the "true" model.

That last bit about "true" models delves into philosophy territory. But the point isn't that Hossenfelder is right or wrong. It's that studying these rudiments and finding holes in them can sometimes be the correct place to go looking for new theory.

And also, I think it's abundantly clear from her tone and choice of words that her bold "prediction" is designed to get you thinking about this stuff in that frame of mind and not something she would actually bet millions on. If I had to guess, she probably feels more akin to Knuth does on P vs NP - that if P does equal NP, it will still have no bearing in practice for other quite interesting reasons.

And absolute confidence that this is the correct take.

Now, I understand that the experimental evidence underpinning modern astrophysics is very, very sound. But if that is truly the end, and no further discoveries of any note are ever to be had beyond Solvay 1927… well, perhaps the modern astrophysics community should just collectively hang it up and start a landscaping business.

My own thoughts as a well-learned armchair physicist is GR is the wrong model and Einstein's field equations aren't the right model allowing us to include gravity in QFT. This is what most actual physicists believe, and for good reason. Of course it's entirely possible that QFT is also the wrong model and we need a completely different model from everything we have today in order to form a theory of everything. That's what String Theory and Brane Theory attempted to do. The problem being is thus far the new models don't predict any different results than does the existing model - they all appear to be equivalent. But you can't know that unless you tried, so it's not a waste of time.

I am pretty sure 99.9% of her colleagues won't state that "this is impossible" when presented a consistent model. Why would they? Why do you do that?

None of the laws and equations hold quantitatively, also the basic objects do not exist, and the basic axioms don't hold either. All of the qualitative results, conservation laws, negative laws that forbid things are total useless.

There is a chance that relativity is wrong, there is no spacetime, there are no frames, E, m and c are useless numbers, and albeit they are definable and measurable, E=mc^2 never ever holds. (< or > holds instead)

Or the same can happen with quantum, there are no states, you can't add states together, Dirac equation never ever holds quantitatively, etc etc.

For instance, Newtonian physics wasn’t demolished by Einstein et al. It was refined, such that Newtonian physics applies very well in scenarios and scales that we would consider ordinary.

But you are completely right. When the theories are unified then people could very well be saying “you can’t just add these states together”, just like I’d often say that when talking about adding speeds together (it doesn’t convince the traffic officer). What I do think, though, is that a perfectly good response to that will be “ah, yes, that isn’t a problem though because this isn’t in the presence of a magnetic, rotating, supermassive black hole with a funny hat on, so the flopookle correction we learned about in physics 201 is negligible”

I was a little surprised by her comment but perhaps generating controversy is her actual point. It seems to me that with the long-standing and seemingly insurmountable gulf between QM and GR there needs to be more controversy—not less.

I've always considered >c discussions and arguments speculative and hypothetical and my view hasn't changed but with the QM/GR elephant in the room perhaps it's time to remind ourselves of a similar controversy. When Galileo proposed his controversial theory that likely >99.9℅ of the establishment was against him or thought him crazy.

Obviously, you meant to use the percent sign (%), but instead have used the "care of" sign (℅). This is the second time in a month I've seen this error, and I'm curious how it can occur.

I did just notice that it's possible to type it on an Android keyboard by long pressing the percent sign. That seems challenging to do by accident. I'm curious if there's another way to easily type it by accident.

Screenshot: https://ibb.co/YdGKwZd

The message was sent from the same Android phone I'm using now. Moreover, I'm still not sure how it happened because the KB app I'm using is OpenBoard and its long-press is '‰'.

I'm curious too because OpenBoard only has the one long-press option (as above) unlike GBoard which has two—the first being '‰' and the second the "care of" sign. Trouble is that GBoard is normally disabled [not just deselected] on this phone and I had to re-enable it to check.

I've noticed occasionally that I've had 'strange' characters appear that do not seem to be long-presses when I've been typing in a hurry so there must be some option for selecting them that I'm unaware of.

It's late here now so I'll investigate later and get back to you when or if I find the answer.

The only way I can see to get the "care of" character, '℅', in OpenBoard is to use the number toggle and then select the alternate list of characters. As I said this is different to GBoard which allows one the choice between '‰' and '℅' in its long-press of the percent key.

In summary I can't see how I could have entered it from the keyboard without toggling the complete change of characters for the keyboard layout I was using and I don't think I did that—but then I must have. Either that or it's the result of spurious characters arising from hitting multiple keys at once that I mentioned in my last comment.

I hope that helps but I'm still not satisfied with what I've found for the reason that I often want to use Unicode characters that are not on the default keys and I'd to extend that list but it doesn't seem possible. At present, my only solution is to use a separate Unicode app to drop the character in and that's a bit of a pain.

I don't.