3 ms·

On the Physics SE a similar cluster of questions are asked about the finiteness of the speed of light e.g https://physics.stackexchange.com/questions/230703/do-

by Jun8 7y ago

On the Physics SE a similar cluster of questions are asked about the finiteness of the speed of light e.g https://physics.stackexchange.com/questions/230703/do-we-know-why-there-is-a-speed-limit-in-our-universe https://physics.stackexchange.com/questions/230703/do-we-kno..., why the Principle of Least Action exists, and the “paradox” of size of the universe being larger than it’s age x c

ShamelessC 7y ago
The linked question on "why is C finite" is a good example. Each answer is basically just "the speed of light is finite because the field I know most about (cosmology, relativity, etc.) breaks in this specific way when it's infinite". Having said that, I do believe the correct answer is some form of "we don't know". But that would be considered a half baked answer according to the author. It's also deeply unsatisfying on an emotional level. So all the answers are basically modifying the intent of the asker in order to answer related questions which _are_ satisfying. This is compounded by the StackExchange community upvoting highly knowledgeable answers. Fortunately you can see the disputes on these answers also get upvotes in the answer's comments.
- knzhou 7y ago
  In theoretical physics, "why X" stands for absolutely nothing more than "please derive X from some other principle". Some people will use Y to derive X. Others will say that's not a real explanation, you really should use Z to derive X. And yet others will flip the derivation around and say that X really is the fundamental principle, and use it to derive Y and Z! (The route one takes depends on what one views as "more fundamental", a metaphysical notion that nobody agrees on.) It's completely fair if you don't think any of the answers were satisfying, but it's not like there's another option on the table. A lot of laypeople think that a truly satisfying answer must be mechanistic -- something like "there's an invisible jelly everywhere and it wobbles at a finite speed, and that is the speed of light" -- but the 20th century taught us that this completely natural desire is actually counterproductive, because you have to add piles of epicycles to hide the jelly's other effects.
  - ShamelessC 7y ago
    Yeah. I think answers which aren't technically correct but are highly knowledgeable and deeply related are still very useful. >"there's an invisible jelly everywhere and it wobbles at a finite speed, and that is the speed of light" As a layperson, is this analogous to "the electromagnetic field is everywhere and wobbles at a finite speed"?
    - knzhou 7y ago
      "Field" is the abstraction we use in physics to say "there is a value associated with each point, and we're just not going to say whether it's representing the displacement of some invisible jelly, or the rotational velocity of some invisible tiny gears, or if it doesn't even make sense to ask the question". When we say the electromagnetic field wobbles, we just mean some abstract value is going from positive to negative and back. I know that sounds unsatisfying, but there's good historical reason for doing this. Maxwell, for example, had a rich intuitive understanding of the electromagnetic field as a set of many invisible jellies and gears pushing on each other. His original equations were also 5x longer than the modern form and impossible for anybody else to understand, plus all the extra ingredients made tons of predictions that played poorly with relativity. The sheer butchery one needs to make intuitive pictures like this compatible with relativity is so high that we've basically collectively decided to give up. We now say fields make up real jellies and gears, they're not made of jellies and gears. They're just fields.
      - ShamelessC 7y ago
        I gotcha. Not the right way to think about it. To be clear, you're saying fields are essentially virtual mathematical notions from which emerges actual stuff? Given the premise that fields are explicitly not consisted of an "invisible jelly", I'll ask what is definitely a "half-assed question" - How and where _do_ fields "exist"? Where are they in the standard model? Intuition says maybe they reside in spacetime near particles. I have a hunch from QFT that the fields are technically "everywhere" and are merely highly excited into particles when energy transforms the field in certain spots. I doubt either of my guesses is the right answer but I'm mostly just curious how literally you mean to take the viewpoint that fields are "virtual" in nature. Since this is a half-assed question, feel free to give a half-assed answer.
- BadThink6655321 7y ago
  Isn’t the ultimate answer always “we don’t know”, “because”, or “42”? It has to be deeply unsatisfying because we don’t know what the ultimate question is, do we? We can’t stop asking.

by Jun8 7y ago

ShamelessC 7y ago

The linked question on "why is C finite" is a good example. Each answer is basically just "the speed of light is finite because the field I know most about (cosmology, relativity, etc.) breaks in this specific way when it's infinite". Having said that, I do believe the correct answer is some form of "we don't know". But that would be considered a half baked answer according to the author. It's also deeply unsatisfying on an emotional level. So all the answers are basically modifying the intent of the asker in order to answer related questions which _are_ satisfying. This is compounded by the StackExchange community upvoting highly knowledgeable answers. Fortunately you can see the disputes on these answers also get upvotes in the answer's comments.

knzhou 7y ago
In theoretical physics, "why X" stands for absolutely nothing more than "please derive X from some other principle". Some people will use Y to derive X. Others will say that's not a real explanation, you really should use Z to derive X. And yet others will flip the derivation around and say that X really is the fundamental principle, and use it to derive Y and Z! (The route one takes depends on what one views as "more fundamental", a metaphysical notion that nobody agrees on.) It's completely fair if you don't think any of the answers were satisfying, but it's not like there's another option on the table. A lot of laypeople think that a truly satisfying answer must be mechanistic -- something like "there's an invisible jelly everywhere and it wobbles at a finite speed, and that is the speed of light" -- but the 20th century taught us that this completely natural desire is actually counterproductive, because you have to add piles of epicycles to hide the jelly's other effects.
- ShamelessC 7y ago
  Yeah. I think answers which aren't technically correct but are highly knowledgeable and deeply related are still very useful. >"there's an invisible jelly everywhere and it wobbles at a finite speed, and that is the speed of light" As a layperson, is this analogous to "the electromagnetic field is everywhere and wobbles at a finite speed"?
  - knzhou 7y ago
    "Field" is the abstraction we use in physics to say "there is a value associated with each point, and we're just not going to say whether it's representing the displacement of some invisible jelly, or the rotational velocity of some invisible tiny gears, or if it doesn't even make sense to ask the question". When we say the electromagnetic field wobbles, we just mean some abstract value is going from positive to negative and back. I know that sounds unsatisfying, but there's good historical reason for doing this. Maxwell, for example, had a rich intuitive understanding of the electromagnetic field as a set of many invisible jellies and gears pushing on each other. His original equations were also 5x longer than the modern form and impossible for anybody else to understand, plus all the extra ingredients made tons of predictions that played poorly with relativity. The sheer butchery one needs to make intuitive pictures like this compatible with relativity is so high that we've basically collectively decided to give up. We now say fields make up real jellies and gears, they're not made of jellies and gears. They're just fields.
    - ShamelessC 7y ago
      I gotcha. Not the right way to think about it. To be clear, you're saying fields are essentially virtual mathematical notions from which emerges actual stuff? Given the premise that fields are explicitly not consisted of an "invisible jelly", I'll ask what is definitely a "half-assed question" - How and where _do_ fields "exist"? Where are they in the standard model? Intuition says maybe they reside in spacetime near particles. I have a hunch from QFT that the fields are technically "everywhere" and are merely highly excited into particles when energy transforms the field in certain spots. I doubt either of my guesses is the right answer but I'm mostly just curious how literally you mean to take the viewpoint that fields are "virtual" in nature. Since this is a half-assed question, feel free to give a half-assed answer.
BadThink6655321 7y ago
Isn’t the ultimate answer always “we don’t know”, “because”, or “42”? It has to be deeply unsatisfying because we don’t know what the ultimate question is, do we? We can’t stop asking.