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posted by Fnord666 on Wednesday March 01 2017, @05:21PM   Printer-friendly
from the seemed-like-a-hack-anyway dept.

The dominant Lambda-CDM model is the standard model of physical cosmology, and it has proved reasonably successful. It does, however, have problems, such as dark matter, whose true nature remains elusive. Dutch physicist Erik Verlinde has, in a recent paper, proposed that gravity might not actually be a fundamental interaction at all, but rather an emergent property of spacetime itself, and as such, what current cosmological theory considers dark matter is really an emergent gravity phenomenon. Sabine Hossenfelder has an article about several recent tests of Verlinde's theory, which show that the idea might have promise.

Physicists today describe the gravitational interaction through Einstein's Theory of General Relativity, which dictates the effects of gravity are due to the curvature of space-time. But it's already been 20 years since Ted Jacobson demonstrated that General Relativity resembles thermodynamics, which is a framework to describe how very large numbers of individual, constituent particles behave. Since then, physicists have tried to figure out whether this similarity is a formal coincidence or hints at a deeper truth: that space-time is made of small elements whose collective motion gives rise to the force we call gravity. In this case, gravity would not be a truly fundamental phenomenon, but an emergent one.

[...] Verlinde pointed out that emergent gravity in a universe with a positive cosmological constant – like the one we live in – would only approximately reproduce General Relativity. The microscopic constituents of space-time, Verlinde claims, also react to the presence of matter in a way that General Relativity does not capture: they push inwards on matter. This creates an effect similar to that ascribed to particle dark matter, which pulls normal matter in by its gravitational attraction.

[...] So, it's a promising idea and it has recently been put to test in a number of papers.

[...] Another paper that appeared two weeks ago tested the predictions from Verlinde's model against the rotation curves of a sample of 152 galaxies. Emergent gravity gets away with being barely compatible with the data – it systematically results in too high an acceleration to explain the observations.

A trio of other papers show that Verlinde's model is broadly speaking compatible with the data, though it doesn't particularly excel at anything or explain anything novel.

[...] The real challenge for emergent gravity, I think, is not galactic rotation curves. That is the one domain where we already know that modified gravity – at last some variants thereof – work well. The real challenge is to also explain structure formation in the early universe, or any gravitational phenomena on larger (tens of millions of light years or more) scales.

Particle dark matter is essential to obtain the correct predictions for the temperature fluctuations in the cosmic microwave background. That's a remarkable achievement, and no alternative for dark matter can be taken seriously so long as it cannot do at least as well. Unfortunately, Verlinde's emergent gravity model does not allow the necessary analysis – at least not yet.

Previously:
Emergent Gravity and the Dark Universe


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  • (Score: 2, Disagree) by Grishnakh on Wednesday March 01 2017, @09:53PM (7 children)

    by Grishnakh (2831) on Wednesday March 01 2017, @09:53PM (#473556)

    This is a far cry from theology, which is primarily human speculation about unobservable entities.

    No, theology goes well beyond just that. It attempts to use logic and rationality to make sense of unobservable entities, by basically assuming that various anecdotes and hearsay over the course of millennia are incontrovertible evidence, and then attempting to reconcile all that.

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  • (Score: 2, Disagree) by HiThere on Thursday March 02 2017, @12:52AM (6 children)

    by HiThere (866) Subscriber Badge on Thursday March 02 2017, @12:52AM (#473645) Journal

    Most theology cannot be justified by appeals to logic, rationality, or any similar construct. It postulates unobservable entities, and then claims that observable happening that have no logical or rational connection to those entities are nevertheless caused by those entities. There are parts of theology that do not follow this pattern, but they are rare and unusual. What theology tends to depend on is appeals to authority, usually an authority that is not in a position to retort that it is being misrepresented.

    --
    Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
    • (Score: 3, Insightful) by Grishnakh on Thursday March 02 2017, @02:08AM (5 children)

      by Grishnakh (2831) on Thursday March 02 2017, @02:08AM (#473672)

      Most theology cannot be justified by appeals to logic, rationality, or any similar construct.

      I disagree. From what I've seen of it, it attempts to look rational, but it's based on "evidence" that is hearsay at best, and quite possibly utter fiction. Basically they take some personal testimony by various people (usually long dead), assume it to be 100% true, and then derive stuff from that.

      Just look at Mormons: they have not only the Book of Mormon (as dictated by Joseph Smith from some golden plates that no one's ever seen), they also have the Book of Abraham [wikipedia.org]. This is actually a real ancient Egyptian text, which is actually a funerary text, but Smith "translated" it as something entirely different, which modern Mormons stridently defend even though every Egyptologist sees them as funerary texts and Joseph Smith knew nothing about Egyptian heiroglyphics. According to Smith's writing, this book says, among other things, that God lives nearest to a star named Kolob. It also says that humans exist in spirit form before being born on Earth, and various other such things. So the LDS church accepts this as 100% true, despite all evidence that Smith's "translation" is pure BS, and then logically deduces various other things from this.

      It's quite possible to come up with all kinds of crazy things logically, when your base assumptions are completely faulty or even wrong.

      • (Score: 1) by khallow on Thursday March 02 2017, @01:06PM (4 children)

        by khallow (3766) Subscriber Badge on Thursday March 02 2017, @01:06PM (#473833) Journal

        I disagree.

        Wouldn't that require actual disagreement? Your stated evidence doesn't show this alleged disagreement. Unless somehow "hearsay", "utter fiction", "long dead personal testimony", "assume 100% true", etc justifies an appeal to logic, rationality, etc.

        • (Score: 2) by Grishnakh on Thursday March 02 2017, @02:46PM (3 children)

          by Grishnakh (2831) on Thursday March 02 2017, @02:46PM (#473874)

          Yes, because you haven't proven your point. For some reason, you seem to think that "logic" necessarily involves starting with a base assumption that's true. It doesn't. You can start out with any assumption you like, and then construct a totally logical system around that assumption. For instance, let's assume there's a god and he hates some groups of people X and Y. He has also said that he wants these people destroyed. There's another group of people, Z, who are close allies of X and Y. Is it logical, then, to infer that it's OK to invade people Z and murder them? Absolutely. It's a perfectly logical thing to do, given those assumptions. Of course, the assumptions are completely wrong, but that's irrelevant. You can derive logical conclusions from wrong assumptions.

          Basically, you seem to have a big problem with understanding exactly what logic *is".

          • (Score: 1) by khallow on Friday March 03 2017, @04:26AM (2 children)

            by khallow (3766) Subscriber Badge on Friday March 03 2017, @04:26AM (#474261) Journal

            For some reason, you seem to think that "logic" necessarily involves starting with a base assumption that's true.

            Er no. Maybe the flat Earther guy?

            You can start out with any assumption you like, and then construct a totally logical system around that assumption.

            Rationality deals with that one. Remember it was "appeals to logic, rationality, or any similar construct".

            • (Score: 2) by Grishnakh on Friday March 03 2017, @04:25PM (1 child)

              by Grishnakh (2831) on Friday March 03 2017, @04:25PM (#474414)

              "Appeals to" is not the same as "firmly grounded in". Religious people I've met really do believe their beliefs are rational. They just don't get that their fundamental assumptions are erroneous and usually baseless.

              • (Score: 1) by khallow on Friday March 03 2017, @05:40PM

                by khallow (3766) Subscriber Badge on Friday March 03 2017, @05:40PM (#474458) Journal

                "Appeals to" is not the same as "firmly grounded in".

                Doesn't have to be. I still don't see the basis for your alleged disagreement with HiThere.

                Religious people I've met really do believe their beliefs are rational.

                With of course, a discussion of the reasoning or logic that followed the assumptions being the basis of the assertion that their beliefs are rational, ie, an appeal to logic, rationality, or any similar construct. HiThere makes an important point however, in that a lot of this supposed logic and reasoning isn't even that. Further what does the belief in one's rationality have to do with the rationality of one's beliefs? If I believe you are a jackalope [wikipedia.org] does that make you one? Somehow I think this is yet another place where belief doesn't quite measure up to reality.

                For a famous example, the 11th century work, The Incoherence of the Philosophers [wikipedia.org] claims among other things that philosophy is deeply flawed because it can't disprove the existence of two god and that things happen only because God wills it. The former is just one of those absurdities that make no sense. Why should philosophy be able to do that, and why do we care if there's one or two such gods? I doubt the author, al-Ghazali's assumptions cover that.

                The second is more subtle. The idea fundamentally is that the dynamics of reality are an illusion and thus, that we shouldn't be interested in them. To use Wikipedia's example, fire doesn't burn cotton when brought together. Instead, God burns the cotton and makes it look like the fire is. al-Ghazali is completely disinterested in why God chooses to fake it that way or in the peculiar consistency of the patterns of God's decisions (if God always burns cotton when it comes too close to fire, that sounds like something we can use, say to prevent ourselves from becoming one of the things that God chooses to burn that day).

                There's no reason his explicit assumptions should force us to be incurious about God's behavior or apparent physical rules. And I doubt al-Ghazali wanted us to be so incurious about the world that we ignore obvious harmful behavior (like ignoring that God burns us fairly consistently when we stick our hands in a fire). But what has gone on is that al-Ghazali warped his arguments irrationally to counter a rival belief system without any concern with the consequences.

                And this is particularly instructive because we can see al-Ghazali making a huge claim in the introduction [newbanner.com] that his beliefs are rational and logical while those of the purported philosophers are not (among a variety of other evils). But the appeals to such things can't cover for the folly that follows.

                They just don't get that their fundamental assumptions are erroneous and usually baseless.

                Again not seeing the basis for your disagreement.