5 ms·

Of course it does. Gravity holds you to that chair because the mass of the earth is attracting the mass of you. This tells us that if you were sat on a chair on

by phaemon 13y ago

Of course it does. Gravity holds you to that chair because the mass of the earth is attracting the mass of you. This tells us that if you were sat on a chair on the moon, the hold on you would be less. Theory with prediction, see? That's what that page doesn't answer: Why do the galaxies appear to be moving away from us?

fargolime 13y ago
> Gravity holds you to that chair... You've explained how the effects of gravity can be predicted, not why gravity holds me to the chair. What is the mechanism that causes the gravity that holds me to the chair? Is it undiscovered gravitons, or what? Likewise you wish to know the mechanism that causes the galaxies to move away from one another. We already know that objects have freedom of movement in space. So why the galaxies appear to be moving away from us can be simply because they are moving away from us. There doesn't need to be a deeper explanation. If you would like to explain the observation using the expanding space paradigm then tell me why space itself is expanding, without saying "it just is". Tell me the mechanism by which it expands. Otherwise you've answered one why question by making an assumption that is left wanting for its own explanation as to why. You've traded one problem for another.
- phaemon 13y ago
  So what? You can ask "why" all the way down, but the effect of you sitting on a chair still has an explanation. I want to know why the galaxies are moving away from each other, because it appears that they should actually be attracted to each other by gravity. You've actually got two problems now: "why are the galaxies moving apart?" and "why isn't gravity working the way we thought it worked?" How is that simpler? EDIT: I forgot; third problem: "why is the sky dark at night?"
  - fargolime 13y ago
    > You can ask "why" all the way down, but the effect of you sitting on a chair still has an explanation. Trading one problem for another doesn't really solve anything. You take issue with the blog post for not answering your question but neither does current cosmology answer your question, except by raising another question. So the blog post doesn't have the disadvantage over current cosmology that you suggested. > "why isn't gravity working the way we thought it worked? Objects can move away from one another other even as they are attracted to one another by gravity. Are you thinking of how the galaxies are thought to be accelerating away from one another (dark energy)? > "why are the galaxies moving apart?" Physics doesn't need to answer that. Why isn't our Moon larger than it is? It's enough for physics that it's possible in principle for the galaxies to be moving apart from one another. If something we observe is thought to be impossible in principle, then physics should change to address that. So maybe you're thinking of accelerating cosmic expansion here (dark energy). > "why is the sky dark at night?" That's Olber's Paradox. It's already explained by the redshift. The faster a galaxy moves away from us the more redshifted it is. At some degree of redshift our eyes receive only 1 photon per century on average, or less. So that spot in the sky is dark.
    - phaemon 13y ago
      > Trading one problem for another doesn't really solve anything. Yes it does. You might as well say, "No-one knows why I'm stuck to this chair and invoking a complicated 'gravity' theory just trades one problem for another". It clearly does have an advantage though: it answers not just that specific point on chairs, but why rocks fall and how planets orbit and allows you to work out how these things would behave in different environments. A "it just is" theory does none of these things. A "we don't know, but we'll try and find out" theory is much better. > Objects can move away from one another other even as they are attracted to one another by gravity. No they can't, unless some external force is applied at some point. You don't just levitate out of your chair at random intervals for no reason. What was the external force applied to the galaxies? Let's leave the other stuff. If we aren't agreed on the simple things, there's no real point discussing anything more complex.
      - fargolime 13y ago
        > A "it just is" theory does none of these things. Sure. But the physics to predict the behavior for galaxies or other objects moving away from one another is already covered by a theory of gravity. When the blog post removes the expanding space paradigm as superfluous, nothing worse results. > What was the external force applied to the galaxies? Now that question makes more sense to me. Because once they're moving there's no mystery. The galaxies are currently attracted to one another by gravity, we can assume, even as they move away from one another. I don't know what caused the galaxies to start moving away from one another. Let's suppose observations instead showed them to be moving toward one another. Would you then ask what started them doing that? Since they'd be moving in some fashion regardless, the only mystery I see is that they are mostly all moving away from one another. Let's suppose the expanding space idea solves the mystery. Well it's not a very good solution because it immediately raises another question: what causes space itself to expand? It also leads to the flatness problem, a major problem of physics. If it's superfluous and its removal solves the flatness problem, physics would be advanced by removing it, even if that mystery remains.
        phaemon 13y ago

by phaemon 13y ago

fargolime 13y ago

> Gravity holds you to that chair... You've explained how the effects of gravity can be predicted, not why gravity holds me to the chair. What is the mechanism that causes the gravity that holds me to the chair? Is it undiscovered gravitons, or what? Likewise you wish to know the mechanism that causes the galaxies to move away from one another. We already know that objects have freedom of movement in space. So why the galaxies appear to be moving away from us can be simply because they are moving away from us. There doesn't need to be a deeper explanation. If you would like to explain the observation using the expanding space paradigm then tell me why space itself is expanding, without saying "it just is". Tell me the mechanism by which it expands. Otherwise you've answered one why question by making an assumption that is left wanting for its own explanation as to why. You've traded one problem for another.

phaemon 13y ago
So what? You can ask "why" all the way down, but the effect of you sitting on a chair still has an explanation. I want to know why the galaxies are moving away from each other, because it appears that they should actually be attracted to each other by gravity. You've actually got two problems now: "why are the galaxies moving apart?" and "why isn't gravity working the way we thought it worked?" How is that simpler? EDIT: I forgot; third problem: "why is the sky dark at night?"
- fargolime 13y ago
  > You can ask "why" all the way down, but the effect of you sitting on a chair still has an explanation. Trading one problem for another doesn't really solve anything. You take issue with the blog post for not answering your question but neither does current cosmology answer your question, except by raising another question. So the blog post doesn't have the disadvantage over current cosmology that you suggested. > "why isn't gravity working the way we thought it worked? Objects can move away from one another other even as they are attracted to one another by gravity. Are you thinking of how the galaxies are thought to be accelerating away from one another (dark energy)? > "why are the galaxies moving apart?" Physics doesn't need to answer that. Why isn't our Moon larger than it is? It's enough for physics that it's possible in principle for the galaxies to be moving apart from one another. If something we observe is thought to be impossible in principle, then physics should change to address that. So maybe you're thinking of accelerating cosmic expansion here (dark energy). > "why is the sky dark at night?" That's Olber's Paradox. It's already explained by the redshift. The faster a galaxy moves away from us the more redshifted it is. At some degree of redshift our eyes receive only 1 photon per century on average, or less. So that spot in the sky is dark.
  - phaemon 13y ago
    > Trading one problem for another doesn't really solve anything. Yes it does. You might as well say, "No-one knows why I'm stuck to this chair and invoking a complicated 'gravity' theory just trades one problem for another". It clearly does have an advantage though: it answers not just that specific point on chairs, but why rocks fall and how planets orbit and allows you to work out how these things would behave in different environments. A "it just is" theory does none of these things. A "we don't know, but we'll try and find out" theory is much better. > Objects can move away from one another other even as they are attracted to one another by gravity. No they can't, unless some external force is applied at some point. You don't just levitate out of your chair at random intervals for no reason. What was the external force applied to the galaxies? Let's leave the other stuff. If we aren't agreed on the simple things, there's no real point discussing anything more complex.
    - fargolime 13y ago
      > A "it just is" theory does none of these things. Sure. But the physics to predict the behavior for galaxies or other objects moving away from one another is already covered by a theory of gravity. When the blog post removes the expanding space paradigm as superfluous, nothing worse results. > What was the external force applied to the galaxies? Now that question makes more sense to me. Because once they're moving there's no mystery. The galaxies are currently attracted to one another by gravity, we can assume, even as they move away from one another. I don't know what caused the galaxies to start moving away from one another. Let's suppose observations instead showed them to be moving toward one another. Would you then ask what started them doing that? Since they'd be moving in some fashion regardless, the only mystery I see is that they are mostly all moving away from one another. Let's suppose the expanding space idea solves the mystery. Well it's not a very good solution because it immediately raises another question: what causes space itself to expand? It also leads to the flatness problem, a major problem of physics. If it's superfluous and its removal solves the flatness problem, physics would be advanced by removing it, even if that mystery remains.
      - phaemon 13y ago