4 ms·

General Relativity is an inherently local theory. QM is inherently nonlocal. In decades of trying, nobody has figured out how to come up with a theory that brid

by danbruc 10y ago

General Relativity is an inherently local theory. QM is inherently nonlocal. In decades of trying, nobody has figured out how to come up with a theory that bridges them. But to add, there are at least ideas, it is not the case that we made no progress at all. I would like to highlight the ER=EPR conjecture [1] by Leonard Susskind and Juan Maldacena. It roughly states that entangled particles are connected by worm holes and that they are therefore not actually separated in space. Personally I prefer a less sensationalist sounding description, that entanglement defines what it means for points in space to be close together or far apart. This avoids constantly visualizing pairs of particle connected by glowing worm holes from science fiction movies. [1] https://en.wikipedia.org/wiki/ER%3DEPR https://en.wikipedia.org/wiki/ER%3DEPR

intrasight 10y ago
You don't need a wormhole, as there are no particles, and therefore nothing is "separated".
- danbruc 10y ago
  I have no idea what you mean, there are obviously particles, we have an entire standard model full of them.
  - intrasight 10y ago
    https://news.ycombinator.com/item?id=12377393 https://news.ycombinator.com/item?id=12377393 My understanding is that there is a growing consensus on this
    - platz 10y ago
      Just because "Particles are epiphenomena arising from fields." You are completely missing the point that the bumps in the field are what we call particles. There can be distances between the bumps/particles and that means that the bumps are "separated", because it matters whether the bumps are next to each other or far away... This is what we mean by separation. No one is saying the field itself doesn't fill all of space (which it does) Furthermore you can still speak of particles just as you can speak of atoms, because it's useful to call the bumps something other than bumps all the time.
      - intrasight 10y ago
        But there are only "bumps" when observed, right?
        platz 10y ago
        no-one knows what is really "there" when unobserved. fields don't get us out of having to interpret the wave equation (the wave equation is a whole different kind of "waviness", it's not the same thing as the field); and the wave equation only lets us calculate probabilities. so we don't know. but it's true that some things don't behave like particles when we're not looking.
    - danbruc 10y ago
      As far as I can tell, I am admittedly not a physicist, this is at least a contentious issue and probably, again as far as I can tell, a popular misconception. Those fields in quantum field theory are mathematical tools, one starts with particles and then defines fields to mathematically handle system where particles are created and annihilated. Think about it, think about all physics you have ever done, in school or wherever. You have probably never dealt with a situation where something was created or destroyed. You need variables to describe all the things you are dealing with, how do you add new variables or get rid of some old variables halfway in your calculation when something is created or destroyed? This is what those fields in Fock space are for, they are mathematical tools to keep track of the number of particles you have in specific states. You do not start with a field and discover that it has quanta behaving like particles, you start with particles and just describe them with fields in order to be able to handle particle creation and annihilation. Here is Nima Arkani-Hamed giving the Salam lectures 2012, a five day series on the state of fundamental physics. I marked [1] about 30 seconds where he is very clear about this. You can also start here [2] and watch about 10 minutes of this lecture where he quickly redevelops the ideas of quantum field theory. Even if you can not follow all the details, you should easily be able to follow the explanation where the fields come from and why. The particles vs fields issue is explicitly discussed three or four times within those 10 minutes. You may of course want to watch the entire lecture series, it is really good and is pretty non-technical in the beginning. The last day I linked to is actually the exception if I remember correctly, the first four days are mostly without math. [1] https://www.youtube.com/watch?v=tnA7bh7dTqY&t=1669 https://www.youtube.com/watch?v=tnA7bh7dTqY&t=1669 [2] https://www.youtube.com/watch?v=tnA7bh7dTqY&t=370 https://www.youtube.com/watch?v=tnA7bh7dTqY&t=370

by danbruc 10y ago

intrasight 10y ago

You don't need a wormhole, as there are no particles, and therefore nothing is "separated".

danbruc 10y ago
I have no idea what you mean, there are obviously particles, we have an entire standard model full of them.
- intrasight 10y ago
  https://news.ycombinator.com/item?id=12377393 https://news.ycombinator.com/item?id=12377393 My understanding is that there is a growing consensus on this
  - platz 10y ago
    Just because "Particles are epiphenomena arising from fields." You are completely missing the point that the bumps in the field are what we call particles. There can be distances between the bumps/particles and that means that the bumps are "separated", because it matters whether the bumps are next to each other or far away... This is what we mean by separation. No one is saying the field itself doesn't fill all of space (which it does) Furthermore you can still speak of particles just as you can speak of atoms, because it's useful to call the bumps something other than bumps all the time.
    - intrasight 10y ago
      But there are only "bumps" when observed, right?
      - platz 10y ago
        no-one knows what is really "there" when unobserved. fields don't get us out of having to interpret the wave equation (the wave equation is a whole different kind of "waviness", it's not the same thing as the field); and the wave equation only lets us calculate probabilities. so we don't know. but it's true that some things don't behave like particles when we're not looking.
  - danbruc 10y ago
    As far as I can tell, I am admittedly not a physicist, this is at least a contentious issue and probably, again as far as I can tell, a popular misconception. Those fields in quantum field theory are mathematical tools, one starts with particles and then defines fields to mathematically handle system where particles are created and annihilated. Think about it, think about all physics you have ever done, in school or wherever. You have probably never dealt with a situation where something was created or destroyed. You need variables to describe all the things you are dealing with, how do you add new variables or get rid of some old variables halfway in your calculation when something is created or destroyed? This is what those fields in Fock space are for, they are mathematical tools to keep track of the number of particles you have in specific states. You do not start with a field and discover that it has quanta behaving like particles, you start with particles and just describe them with fields in order to be able to handle particle creation and annihilation. Here is Nima Arkani-Hamed giving the Salam lectures 2012, a five day series on the state of fundamental physics. I marked [1] about 30 seconds where he is very clear about this. You can also start here [2] and watch about 10 minutes of this lecture where he quickly redevelops the ideas of quantum field theory. Even if you can not follow all the details, you should easily be able to follow the explanation where the fields come from and why. The particles vs fields issue is explicitly discussed three or four times within those 10 minutes. You may of course want to watch the entire lecture series, it is really good and is pretty non-technical in the beginning. The last day I linked to is actually the exception if I remember correctly, the first four days are mostly without math. [1] https://www.youtube.com/watch?v=tnA7bh7dTqY&t=1669 https://www.youtube.com/watch?v=tnA7bh7dTqY&t=1669 [2] https://www.youtube.com/watch?v=tnA7bh7dTqY&t=370 https://www.youtube.com/watch?v=tnA7bh7dTqY&t=370