Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Nobel Prize in Physics 2025

nobelprize.org

Post reply on HN
Print view View original

71–80 of 110 posts

Re: Nobel Prize in Physics 2025

#71

Post by sbenerofe »

everdrive wrote: post #54

Dumb question: "We know that the ball will bounce back every time it is thrown at a wall. A single particle, however, will sometimes pass straight through an equivalent barrier in its microscopic world and appear on the other side. This quantum mechanical phenomenon is called tunnelling." Is the particle just failing to collide with the wall since objects are mostly empty space? Or is something more spooky or interes…

Not a dumb question at all.

The idea that a particle could pass through a wall by luckily avoiding collisions is a classical way of thinking. In that view, a particle is a tiny solid ball and a wall is just a collection of other tiny balls with space between them.

Quantum tunneling is based on a completely different concept. In quantum mechanics, the "wall" is not a physical object but a high energy barrier. Classically, a particle cannot be in a region if it doesn't have enough energy to overcome that barrier (this is why people often use the idea of a high wall and a ball that cannot make it over the wall). However, quantum mechanics treats particles as having wave-like properties. This wave is related to the probability of finding the particle at any given location. While the probability of finding the particle inside the high-energy barrier is very low, it is not zero. The wave's amplitude shrinks inside the barrier, but a small portion of it extends to the other side. This means there is a small but finite probability that if you measure the particle's position, you will find it on the other side. When that happens, we say the particle has "tunneled" through.

The surprising success of the experiments that led to the Nobel Prize today is that it wasn’t just a single particle (like an electron) that they measured tunneling through a barrier, it was a macroscopic group of particles. These particles were able to tunnel through the barrier because they were kept in a coherent state that allowed them to have a wave function that coherently extended through the barrier. This meant that they had a reasonable finite amplitude on the other side of the barrier so that a measurement could show that they tunneled through the barrier.

Re: Nobel Prize in Physics 2025

#72

Post by cvoss »

everdrive wrote: post #54

Dumb question: "We know that the ball will bounce back every time it is thrown at a wall. A single particle, however, will sometimes pass straight through an equivalent barrier in its microscopic world and appear on the other side. This quantum mechanical phenomenon is called tunnelling." Is the particle just failing to collide with the wall since objects are mostly empty space? Or is something more spooky or interes…

It's more spooky and interesting. When we switch to discussing the single particle case, the "wall" is a metaphor. You have a single particle in a low energy state at position A. There is another low energy state at position C, but the path from A to C entails (ostensibly) passing through an intermediate high energy state at position B. Without lending energy into the system, you wouldn't expect the particle to be able to move from A to C, because the particle needs a lot of energy temporarily to move from A to B (which it would give up again as it moves from B to C). Yet the particle does move from A to C, in the absence of an energy source that could explain what happened. This raises the spooky question: Did it actually pass through B on its way? It seems like it did not.

Re: Nobel Prize in Physics 2025

#73

Post by bookofjoe »

Intermernet wrote: post #12

I remember being introduced to this research when reading a weird paper on the unexpected efficiency of photosynthesis, but now I can't find that paper. Anyone got any hints?

>Quantum efficiency of photosynthetic energy conversion [1977]

https://pmc.ncbi.nlm.nih.gov/articles/PMC431568/

>Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems [2007]

https://www.nature.com/articles/nature05678

>Explaining the Efficiency of Photosynthesis: Quantum Uncertainty or Classical Vibrations? [2022]

https://pubs.acs.org/doi/10.1021/acs.jpclett.2c00538

>Reassessing the role and lifetime of Qx in the energy transfer dynamics of chlorophyll a [2025]

https://pubs.rsc.org/en/content/articlelanding/2025/sc/d4sc0...

>Full microscopic simulations uncover persistent quantum effects in primary photosynthesis [2025]

https://www.science.org/doi/10.1126/sciadv.ady6751

Re: Nobel Prize in Physics 2025

#74

Post by everdrive »

sbenerofe wrote: post #71
everdrive wrote: post #54

Dumb question: "We know that the ball will bounce back every time it is thrown at a wall. A single particle, however, will sometimes pass straight through an equivalent barrier in its microscopic world and appear on the other side. This quantum mechanical phenomenon is called tunnelling." Is the particle just failing to collide with the wall since objects are mostly empty space? Or is something more spooky or interes…

Not a dumb question at all. The idea that a particle could pass through a wall by luckily avoiding collisions is a classical way of thinking. In that view, a particle is a tiny solid ball and a wall is just a collection of other tiny balls with space between them. Quantum tunneling is based on a completely different concept. In quantum mechanics, the "wall" is not a physical object but a high energy barrier. Classica…

Thanks, I'm still thinking about your answer but really appreciate your explanation. Would this mean that there is some (possibly currently unknown) maximum size for a group of particles that could be forced to maintain the correct state to pass through the wall?

Re: Nobel Prize in Physics 2025

#75

Post by chrysander »

correlator wrote: post #67
chrysander wrote: post #30

More than deserved! Both Devoret and Martinis are also highly involved in pushing quantum engineering to new levels - Devoret at Google Quantum AI and Martinis (formerly at Google) with his company, Qolab. Coincidentally, I have a close friend doing his PhD with Devoret and know someone working with Martinis. I am curious to see if they will ever see their respective supervisors again, given that the Nobel Prize atte…

Definitely agree! It's just strange seeing Devoret without Schoelkopf!

And Girvin as the third one of their Yale effort!

Re: Nobel Prize in Physics 2025

#76

Post by IAmBroom »

averne_ wrote: post #32
SiempreViernes wrote: post #26

Earlier quoted context omitted.

They discovered that the theory worked in a regime it hadn't been tested before; I'm not sure what "new physics" means in your sentence: it is a core assumption of physics that it's rules are always true, that all physics has always existed.

New physics in this context means previously unknown effects or mechanisms, or even a new theory/framework for an already understood phenomenon. Using "physics" in this way is common amongst academics.

Do you have two aliases on HN, or are you simply presuming to speak for the OP?

Re: Nobel Prize in Physics 2025

#77

Post by IAmBroom »

Roark66 wrote: post #37
Metacelsus wrote: post #23

This award involved some clever engineering to set up quantum effects in a macroscopic system, but was there any new physics involved here? (Still better than last year's award which wasn't really physics at all!)

Exactly, also in it's goal to "demonstrate quantum tunneling macroscopically" haven't we had tunneling diodes for quite a while? The device uses tunneling for its basic functionality

I thought this too, at first. Then I read the article, and discovered it was about more than Josephson gaps and Schottky diodes.

Re: Nobel Prize in Physics 2025

#78

Post by fraserphysics »

I read the NY Times article about this earlier this morning. I thought it was not very good. I came to HN to see if it had something better. It did. The linked article is also at something like a high school level, but it gave me (retired PhD Physics) a good idea of the experiment and the theory. Thanks.

Re: Nobel Prize in Physics 2025

#79

Post by qnleigh »

everdrive wrote: post #74
sbenerofe wrote: post #71

Earlier quoted context omitted.

Not a dumb question at all. The idea that a particle could pass through a wall by luckily avoiding collisions is a classical way of thinking. In that view, a particle is a tiny solid ball and a wall is just a collection of other tiny balls with space between them. Quantum tunneling is based on a completely different concept. In quantum mechanics, the "wall" is not a physical object but a high energy barrier. Classica…

Thanks, I'm still thinking about your answer but really appreciate your explanation. Would this mean that there is some (possibly currently unknown) maximum size for a group of particles that could be forced to maintain the correct state to pass through the wall?

This is another great question. It's still a matter of debate how the wave-like behavior of quantum mechanics turns into the particle-like behavior of large objects that we observe. Some people believe there should be a maximum size, some people believe that there isn't. In fact Nature did a survey a few months ago and found that physicists disagree wildly on this topic. https://www.nature.com/articles/d41586-025-02342-y

Have you heard of Schrodinger's cat, which is hypothetically dead and alive at the same time? Schrodinger described this thought experiment to argue that quantum mechanics led to absurdities if you took it too far. Ironically, many physicists now believe that such an experiment is possible in principle, though it would be extremely difficult.

Post reply on HN