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Comment by markus_zhang | Hacker News Reader

Just curious but why?

Quantum Physics and General Relativity make different predictions in specific circumstances which are beyond our ability to test to figure out which one is wrong. They can't both be perfectly correct. But in every test we can make, both seem to model reality really well.

The best place to look for new data where we might find reality disagreeing with either model is in the extreme parts of the universe, like black holes. If there was even a hint in this photo that General Relativity wasn't perfectly accurate, we might be able to take the discrepancy and build a new model that solves the disagreement.

Whoever does that gets a Nobel Prize and has their name as immortalized as "Einstein".

Relatedly, before general relativity, people already knew something was wrong with Newton's theory of gravity from observing the orbit of Mercury, which didn't follow the theory accurately. At that time Mercury, being so close to the Sun, was an extreme condition that showed the flaws in the theory.

The fact that general relativity continues to hold up to every observation we can make is remarkable.

Could it happen that the universe simply never provides us with the required evidence? Eg if there's an anomaly but only when something that never happens happens. Like a large enough mass/charge/etc or some flavor of unlikely coincidental occurrence, like an eclipse is a bit of a coincidence.

I've heard it said as "The universe is under no obligation to make sense to us". It's possible that the events where the two theories diverge will always be out of reach for us to observe.

I'd be willing to bet that the discrepancy is something that we generally consider invariant but in reality should be a ratio between two things that are very large, but get bigger or smaller at _slightly_ different rates depending on the scale or distances you're working with.

Granted, I only ever got as far as E&M physics in college so I could be way off here but that scenario has turned up so many times in history.

GR and quantum field theory don't work together, so at least one of them is wrong, and it would be good to figure out which and how.

so at least one of them is wrong

This is a semantic nitpick, but I don’t think it’s useful to think of these theories as “wrong”. They are both models that make predictions about physical phenomena that, when tested, are extremely accurate. They provide incomplete and inconsistent predictions of what happens at the very edges of physical reality, and they need reconciled.

You're saying this team has proven neither of them wrong in that their findings agree with GR, is that correct? Essentially, nothing new has been learned about these two theories?

GR and QFT essentially have to meet at black holes and this is where you’d expect to find an anomaly with ought to help open doors to new physics, but what we see here is that this observation seems to still obey GR just fine and a a closer look will be necessary to find any anomaly.

It might just not be possible to see anything odd without having a black hole right there to study, but there’s always hope that the next new observation will provide a clue as the previous ones repeatedly have not.

Thanks. Can you please point me to some popular science article that explains why the two do not agree with each other?

Here are a few that might help:

https://gizmodo.com/why-cant-einstein-and-quantum-mechanics-...

https://www.theguardian.com/news/2015/nov/04/relativity-quan...

https://en.wikipedia.org/wiki/Problem_of_time

https://physics.stackexchange.com/questions/387/a-list-of-in...

For a good general source if you want to learn a lot more from a good popular science point of view (but one that takes great care to not accidentally mislead by oversimplification as often happens with popular science) about general relativity and quantum mechanics, try PBS Space Time, especially after Dr. Matt O'Dowd took over as host and main writer.

https://www.youtube.com/c/pbsspacetime

Brian Greene's "The Elegant Universe" does a very good, completely non-technical, job of explaining the conflict between the two theories. It then goes on to explain why String Theory is one possible solution to the problem.

There's also a Nova documentary version if parent would prefer to watch something: https://www.pbs.org/wgbh/nova/series/the-elegant-universe/

I'll add an additional recommendation: Stephen Hawking - The Theory Of Everything

Perfect! Thank you.

I liked Sean Carroll's take on this with Steven Strogatz in the recent episode of Joy of Why.

https://www.quantamagazine.org/where-do-space-time-and-gravi...

tl;dr they don't conflict with each other, they conflict with a third assumption that particles have zero size. GR suggests they would be black holes, and those have mathematical difficulties. String theory is an attempt to model particles of finite size and thus eliminate black holes.

Why would that matter at this scale ?

Black holes are extreme enough to be one of the places where both can matter.

Scale was not the right word - maybe I meant distance or resolution. Does QM make a prediction that could be falsified at this resolution?

They want an exciting disruption to current theory.

Side note: Einstein didn't believe in black holes, at least initially.

Black holes are a solution to the general relativity equations, but Einstein thought they were just a mathematical quirk, and that in real life, they wouldn't have been able to form.

So ever time someone says "Einstein was right" when talking about black holes, then no. He was right about general relativity, but he was wrong about the existence of black holes.

Basically they're bored/want mysteries to solve.

We're kind of at a dead end between both leading theories. A counterexample to either of them would mean that we got it wrong somewhere, and might help us figure out where, potentially unlocking more later.

You wouldn't be surprised if your door opened just as usual when you put your key in the lock. The day it starts jamming however, you get very interested.

tbf, there is already a mystery to solve. This just means we have no new information to help us solve it.

Sometimes physicists like the theories--especially the battle-tested ones--proven wrong so that those theories needs to be refined or reevaluated. Something related to the joy of problem solving.

Many papers/authors postulating something different to what Einstein did?

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