A New Test for Quantum Gravity

some people dream of meeting Albert Einstein I wonder what Einstein might have been dreaming of he famously said that God does not row dice to express his dislike of anything related to quantum physics and this makes me suspect that one of his nightmares must have been that his theory of gravity would also be turned into a quantum theory this nightmare seems to be inching closer and closer but not in the way that Einstein might have thought Einstein was very much a theoretical physicist but after trying their hands at developing a theory of quantum gravity and failing physicists are now trying to measure the effects of such a theory there are several proposals for experiments around now and just last week we had a strong newcomer let's have a look as a student I was fascinated by this problem that even Einstein couldn't solve how do we make gravity compatible with with quantum physics the problem isn't all that hard to understand you see a Quantum particle can be in two places at once it's not like the particle splits and half of it is in one place and the other half elsewhere the particle is both entirely in one place and in another at the same time but what happens with its gravitational pull you'd think that this has to go to both places at the same time too but in Einstein's theory of gravity this can't happen happen because it doesn't have Quantum properties so what gives for a long time physicists thought that quantizing gravity was a question of mathematics not experiment they thought that if they could just figure out how they could deduce the right solution but it's become increasingly clear that this just doesn't work with that Focus has shifted to experiment which I think is a very good development the idea is to experimentally test quantum gravity can roughly be classified into two categories in one category are those which want to look at the situation when gravity is strong but for this you need to be inside a black hole or at the Big Bang or you need to have a collider the size of the Milky Way it's very difficult when gravity is weak it's much easier to measure its Quantum effects still not easy but easier because you can actually create these cases in the laboratory but then you have to find find a way to Tel aart the case when gravity is quantum in nature and when it's not and then you need to be able to measure it precisely enough previously we had two different proposals for how to do this and now we have a third the first one is to use what's called an entanglement witness the idea is to take two masses that interact only gravitationally then you show that they have become entangled entanglement can only be created by an interaction that itself has Quantum properties so this had show that gravity must also have Quantum properties the problem I see with this idea is that it will be basically impossible to prove the entanglement wasn't caused by anything else there are several groups working on this now nevertheless for example at the University of Warick and at the University of groing and in the Netherlands the second idea is to directly measure the effects of the gravitational pull on a test m and see how large the uncertainty is suppose you have a Quantum particle that flies left to right as it flies it spreads out because that's what Quantum particles do now suppose you have another object that is in two places at once and much more massive so it'll gravitationally attract the first but how it does so depends on whether gravity has Quantum properties if the gravitational pool does not have Quantum properties and is instead smeared up out over these two places then that has the same effect as if half of the mass was here and the other half there this will cause some spread of the particle that passes by but if the gravitational pull goes to two places at once each with the full mass of the object that'll spread the particles directions even further to measure this you want to take an object that's as heavy as possible and bring it into a Quantum super position there are people working on this now for example in Vienna the new paper now comes up with a third idea that I hadn't heard previously it's to measure what Quantum systems do when you don't look at them concretely they use two masses connected by a rod and suspended from a wire this is known as a torsion pendulum they're commonly used to measure small gravitational attractions because say you put a mass nearby this thing then the ulum will turn and you can measure this from The Twist of the wire which is very practical they now say we set up those masses so that two of the pendular coupled together but you know this is quantum physics so nothing ever sits entirely still everything always Wiggles a bit and the question is how the wiggling of each pendulum affects the wiggling of the other one so you set up the pendular wait for a bit and let them wiggle and interact measure what they're doing and then you repeat this a billion times in the paper they've calculated that if gravity itself has Quantum properties then there are many more possible outcomes than If gravity is not Quantum basically more things can happen this is a very promising approach because it's easier than measuring entanglement and one doesn't need to bring the objects in strongly delocalized States what could all of this be good for is it just putting the finishing touches on Einstein's Masterwork I think it's much more than this solving this problem will quite possibly also help solve other problems like the nature of dark energy or dark matter or what's going on in a measurement in quantum mechanics so stay tuned and um one thing my agency says that few of you have turned on notifications for this Channel and I'm supposed to tell you to do it so please turn on notifications because otherwise they'll make me repeat this watching science videos is all well and fine and I don't mean to complain you're doing it but it's not a good way to actually learn something new if you want to learn something new you need to actively engage with the topic a free and easy way to do this is on brilliant.org who've been sponsoring this video on brilliant you find courses on a large variety of Topics in science computer Science and Mathematics I even have my own course there that's an introduction to Quantum Mechanics and all their courses are interactive with visualizations and follow-up questions brilliant really makes learning easy fun and also convenient because you can do it whenever and wherever you like and of course I have a special offer for viewers of this channel if you use my link brilliant.org Saina you'll get to try everything brilliant has to offer for free for 4 30 days and you'll get 20% off an annual premium subscription links in the description below so go and check those out thanks for watching see you tomorrow

Channel: Sabine Hossenfelder

Views: 174,187

Keywords: science without the gobbledygoook, hossenfelder, science news sabine, science news, science humor, quantum, quantum gravity, Einstein, Einstein’s theory of gravity, mathematics, entanglement witness, quantum properties, physics, physics news, science short video, science news short, science news daily, science news 2024

Id: I0uaZvvgPTo

Length: 7min 45sec (465 seconds)

Published: Thu May 16 2024