5 ms·

> In your explanation, I think we'd expect to see some very distant, very slow-moving galaxies moving toward us Thank you, but I suppose I'm not really questio

> In your explanation, I think we'd expect to see some very distant, very slow-moving galaxies moving toward us Thank you, but I suppose I'm not really questioning the big bang piece. My question was mostly in regards to the continued acceleration piece. Feel free to disregard the "in random directions" part of my original post. I'm picturing more of an explosion in empty space. A firework or granade of sorts. Any individual dust/shard of the explosion still sees all other objects moving away from it and the rest of my question stands. But I suppose this would imply a "center" to the explosion, which I've also heard is not the case. Theres a few other comments offering more clarity to the acceleration piece. Thank you everyone!

pdonis 3y ago
> I'm picturing more of an explosion in empty space. No, that's not what the big bang is. > this would imply a "center" to the explosion, which I've also heard is not the case That's correct. The big bang does not work like anything ordinary that you are used to imagining. The math is straightforward and unambiguous, but there is no good ordinary language description that corresponds to the math.
- alexb23 3y ago
  I find helpful this analogy of the space-time (4-dimension) expansion from the big bang: the surface (2D) of an expanding bubble. YMMV.
- lp4vn 3y ago
  As I understand it, before the big bang the whole observable universe was contained in a small sphere and then it started to expand metrically. Is this interpretation correct? Another thing: suppose I point a laser beam to the space and by chance this laser beam never finds any kind of matter in its way, where is this laser going to? To an infinite void? Is it correct to say that stars radiate energy to the infinite then?
  - pigpang 3y ago
    It's just an interpretation. Your interpretation is similar to the Big Bang model of visible Universe expansion. If you can convince us that your model is better than other models, then we will use your model, but nobody can prove than a model is correct, unless we will find a hidden recorder somewhere which was turned on for few dozens of billion years. Photon will hit something, or will travel until it will be redshifted to obvilion, or will travel until end of the medium (photon is a wave, so it waves something).
    - denton-scratch 3y ago
      > (photon is a wave, so it waves something) That sounds suspiciously like postulating the 'ether'. Surely what a photon 'waves' is the electromagnetic field, which is not a medium, and which fills the whole of spacetime. There is no 'end of the medium'.
      - pigpang 3y ago
        "Field" means 3d array of numbers. Spacetime means 4d array of numbers. You are talking about mathematical model of Universe, while I'm talking about physics. Mountain is not just an excitement in a height field. If photon is not waving something, then it's not a wave. Physicists prove that photon is a wave.
        michaelsbradley 3y ago
        > If photon is not waving something, then it's not a wave. No, you’ve simply hit the limits of needing/wanting to understand something in terms of something else similar or more familiar. Makes the same point on a related matter: https://youtu.be/Q1lL-hXO27Q https://youtu.be/Q1lL-hXO27Q
    - pdonis 3y ago
      > It's just an interpretation No, it's not, it's our best current model's description of the actual physical reality of our universe. > nobody can prove than a model is correct That's true, but it's also true that we can show models to be incorrect, as in, falsified by the data. For example: > Photon will hit something, or will travel until it will be redshifted to obvilion, or will travel until end of the medium For the scenario that was posed, a laser beam that never hits anything, none of your statements here are true. The first is ruled out by the scenario; the second is known to be false because there is no "gravitational redshift" of light in the universe as a whole (because models in which there would be such a redshift are known not to correctly model our data on the universe as a whole), and there is no "end of the medium" (again, models in which there would be an "end of the medium", i.e., where the universe stopped containing matter and started being just vacuum, are known not to correctly model our data). I have described what actually happens in my own response to the GP upthread. > (photon is a wave, so it waves something). Light is an electromagnetic wave; what "waves" is the electromagnetic field. (If you use a "photon" model, you are using the quantum electromagnetic field as opposed to its classical approximation.) There doesn't have to be any other "medium"; the electromagnetic field is present everywhere.

pdonis 3y ago

> I'm picturing more of an explosion in empty space. No, that's not what the big bang is. > this would imply a "center" to the explosion, which I've also heard is not the case That's correct. The big bang does not work like anything ordinary that you are used to imagining. The math is straightforward and unambiguous, but there is no good ordinary language description that corresponds to the math.

alexb23 3y ago
I find helpful this analogy of the space-time (4-dimension) expansion from the big bang: the surface (2D) of an expanding bubble. YMMV.
lp4vn 3y ago
As I understand it, before the big bang the whole observable universe was contained in a small sphere and then it started to expand metrically. Is this interpretation correct? Another thing: suppose I point a laser beam to the space and by chance this laser beam never finds any kind of matter in its way, where is this laser going to? To an infinite void? Is it correct to say that stars radiate energy to the infinite then?
- pigpang 3y ago
  It's just an interpretation. Your interpretation is similar to the Big Bang model of visible Universe expansion. If you can convince us that your model is better than other models, then we will use your model, but nobody can prove than a model is correct, unless we will find a hidden recorder somewhere which was turned on for few dozens of billion years. Photon will hit something, or will travel until it will be redshifted to obvilion, or will travel until end of the medium (photon is a wave, so it waves something).
  - denton-scratch 3y ago
    > (photon is a wave, so it waves something) That sounds suspiciously like postulating the 'ether'. Surely what a photon 'waves' is the electromagnetic field, which is not a medium, and which fills the whole of spacetime. There is no 'end of the medium'.
    - pigpang 3y ago
      "Field" means 3d array of numbers. Spacetime means 4d array of numbers. You are talking about mathematical model of Universe, while I'm talking about physics. Mountain is not just an excitement in a height field. If photon is not waving something, then it's not a wave. Physicists prove that photon is a wave.
      - michaelsbradley 3y ago
        > If photon is not waving something, then it's not a wave. No, you’ve simply hit the limits of needing/wanting to understand something in terms of something else similar or more familiar. Makes the same point on a related matter: https://youtu.be/Q1lL-hXO27Q https://youtu.be/Q1lL-hXO27Q
  - pdonis 3y ago
    > It's just an interpretation No, it's not, it's our best current model's description of the actual physical reality of our universe. > nobody can prove than a model is correct That's true, but it's also true that we can show models to be incorrect, as in, falsified by the data. For example: > Photon will hit something, or will travel until it will be redshifted to obvilion, or will travel until end of the medium For the scenario that was posed, a laser beam that never hits anything, none of your statements here are true. The first is ruled out by the scenario; the second is known to be false because there is no "gravitational redshift" of light in the universe as a whole (because models in which there would be such a redshift are known not to correctly model our data on the universe as a whole), and there is no "end of the medium" (again, models in which there would be an "end of the medium", i.e., where the universe stopped containing matter and started being just vacuum, are known not to correctly model our data). I have described what actually happens in my own response to the GP upthread. > (photon is a wave, so it waves something). Light is an electromagnetic wave; what "waves" is the electromagnetic field. (If you use a "photon" model, you are using the quantum electromagnetic field as opposed to its classical approximation.) There doesn't have to be any other "medium"; the electromagnetic field is present everywhere.