5 ms·

Related article from The Guardian: https://www.theguardian.com/science/2024/mar/09/controversial-new-theory-of-gravity-rules-out-need-for-dark-matter https://ww

Related article from The Guardian: https://www.theguardian.com/science/2024/mar/09/controversial-new-theory-of-gravity-rules-out-need-for-dark-matter https://www.theguardian.com/science/2024/mar/09/controversia...

dbacar 3y ago
Thank you, this is much more accessible for me.
boxed 3y ago
That sounds very unconvincing. Afaik there are several found galaxies with more than normal amounts of dark matter, and less. How would these fit into ANY modified gravity theory? This type of theory seems to only handle the common case, but the universe is full of edge cases...
- scotty79 3y ago
  If the base of this theory is some form of chaos you can always fit the distribution of the chaos to explain outliers with the probability they actually occur at.
  - BlueTemplar 3y ago
    Can you ? How is this different from, say, anything involving pressure and temperature, which under current theories, are statistical phenomena arising from quantum behaviour, fundamentally based on our lack of information about what is going on (aka entropy) ?
    - scotty79 3y ago
      I think technically you can. Although it's just moving the question to "why is the chaos distributed like that?". Current explanation for existence of galaxies is those are quantum fluctuations that grew large. So apparently fluctuations can explain everything if you do enough of hand waving in between. I don't think any particular quality of galaxies as we see them today can be traced to specific quantum property. But that doesn't stop us from believing in that explanation.
      - data_maan 3y ago
        Isn't that already enough to know that it is some form chaos that underlies many of the current phenomena? For any explanation X there will always be the question, "now what explains X"?
    - Vecr 3y ago
      I don't think entropy can be defined as your lack of knowledge, at least straight out. You have to be careful as under strict Bayesianism knowledge can't ever decrease, implying that entropy is monotonically non-increasing, and that's clearly wrong.
      - BlueTemplar 3y ago
        Then I'll side with Bayesianism being wrong rather than statistical physics being wrong : http://www.av8n.com/physics/thermo/entropy.html#sec-s-not-knowing http://www.av8n.com/physics/thermo/entropy.html#sec-s-not-kn... http://www.av8n.com/physics/thermo/entropy-more.html#sec-s-context http://www.av8n.com/physics/thermo/entropy-more.html#sec-s-c... http://www.av8n.com/physics/thermo/s-relevance.html#ch-s-relevance http://www.av8n.com/physics/thermo/s-relevance.html#ch-s-rel...
        Vecr 3y ago
        Bayesianism is not wrong (it more or less can't be), the main problem is exactly what you mean by "knowing" and "entropy". Obviously, an embedded agent knowing from within physics is limited, but that's not a problem with theoretical Bayesianism, and it's not a problem if you're dealing with cards.
        BlueTemplar 3y ago
        Wrong when applied in the general context of fundamental physics ?? (See also how entropy can often be approximated as an objective and property of a system, its density intensive, but in the general case that's wrong.) Speaking of, I'm somewhat puzzled, you said that "under strict Bayesianism knowledge can't ever decrease", but how does it then deal with something as simple as card shuffling ??
        Vecr 3y ago
        Depending on how you want to do it, the hypotheses that get probabilities can be represented as computer programs that predict the input the agent receives. If done correctly (perfectly if you want it to be absolute) the probability-weighted sum of the calibration metrics won't ever go down.
  - boxed 3y ago
    That makes no sense. You can't form entire stable galaxies and have them rotate cleanly in a disk for millions of years with "chaos".
- floxy 3y ago
  If a new theory fits 199,999,999,985 galaxies, you deal with the remaining 15 edge cases one at a time.
  - boxed 3y ago
    I hope that was sarcasm...
layer8 3y ago
The Guardian headline stands in contradiction to this statement from the paper’s abstract: “We caution that a greater understanding of this effect is needed before conclusions can be drawn”.
- bloopernova 3y ago
  The byline specifically says: "Exclusive: Paper by UCL professor says ‘wobbly’ space-time could instead explain expansion of universe and galactic rotation" "Could instead explain" is not a definitive statement. Their headline is "Controversial new theory of gravity rules out need for dark matter" "Controversial new" tells me that this isn't settled science, nor is the Guardian trying to say otherwise. "Rules out" by itself, out of context, could imply proven science, but not within the context of the headline and byline.

dbacar 3y ago

Thank you, this is much more accessible for me.

boxed 3y ago

That sounds very unconvincing. Afaik there are several found galaxies with more than normal amounts of dark matter, and less. How would these fit into ANY modified gravity theory? This type of theory seems to only handle the common case, but the universe is full of edge cases...

scotty79 3y ago
If the base of this theory is some form of chaos you can always fit the distribution of the chaos to explain outliers with the probability they actually occur at.
- BlueTemplar 3y ago
  Can you ? How is this different from, say, anything involving pressure and temperature, which under current theories, are statistical phenomena arising from quantum behaviour, fundamentally based on our lack of information about what is going on (aka entropy) ?
  - scotty79 3y ago
    I think technically you can. Although it's just moving the question to "why is the chaos distributed like that?". Current explanation for existence of galaxies is those are quantum fluctuations that grew large. So apparently fluctuations can explain everything if you do enough of hand waving in between. I don't think any particular quality of galaxies as we see them today can be traced to specific quantum property. But that doesn't stop us from believing in that explanation.
    - data_maan 3y ago
      Isn't that already enough to know that it is some form chaos that underlies many of the current phenomena? For any explanation X there will always be the question, "now what explains X"?
  - Vecr 3y ago
    I don't think entropy can be defined as your lack of knowledge, at least straight out. You have to be careful as under strict Bayesianism knowledge can't ever decrease, implying that entropy is monotonically non-increasing, and that's clearly wrong.
    - BlueTemplar 3y ago
      Then I'll side with Bayesianism being wrong rather than statistical physics being wrong : http://www.av8n.com/physics/thermo/entropy.html#sec-s-not-knowing http://www.av8n.com/physics/thermo/entropy.html#sec-s-not-kn... http://www.av8n.com/physics/thermo/entropy-more.html#sec-s-context http://www.av8n.com/physics/thermo/entropy-more.html#sec-s-c... http://www.av8n.com/physics/thermo/s-relevance.html#ch-s-relevance http://www.av8n.com/physics/thermo/s-relevance.html#ch-s-rel...
      - Vecr 3y ago
        Bayesianism is not wrong (it more or less can't be), the main problem is exactly what you mean by "knowing" and "entropy". Obviously, an embedded agent knowing from within physics is limited, but that's not a problem with theoretical Bayesianism, and it's not a problem if you're dealing with cards.
        BlueTemplar 3y ago
        Wrong when applied in the general context of fundamental physics ?? (See also how entropy can often be approximated as an objective and property of a system, its density intensive, but in the general case that's wrong.) Speaking of, I'm somewhat puzzled, you said that "under strict Bayesianism knowledge can't ever decrease", but how does it then deal with something as simple as card shuffling ??
        Vecr 3y ago
        Depending on how you want to do it, the hypotheses that get probabilities can be represented as computer programs that predict the input the agent receives. If done correctly (perfectly if you want it to be absolute) the probability-weighted sum of the calibration metrics won't ever go down.
- boxed 3y ago
  That makes no sense. You can't form entire stable galaxies and have them rotate cleanly in a disk for millions of years with "chaos".
floxy 3y ago
If a new theory fits 199,999,999,985 galaxies, you deal with the remaining 15 edge cases one at a time.
- boxed 3y ago
  I hope that was sarcasm...

layer8 3y ago

The Guardian headline stands in contradiction to this statement from the paper’s abstract: “We caution that a greater understanding of this effect is needed before conclusions can be drawn”.

bloopernova 3y ago
The byline specifically says: "Exclusive: Paper by UCL professor says ‘wobbly’ space-time could instead explain expansion of universe and galactic rotation" "Could instead explain" is not a definitive statement. Their headline is "Controversial new theory of gravity rules out need for dark matter" "Controversial new" tells me that this isn't settled science, nor is the Guardian trying to say otherwise. "Rules out" by itself, out of context, could imply proven science, but not within the context of the headline and byline.