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
Related Stories
Theoretical physicist Eric Verlinde has finally published his much anticipated article on the nature of gravity. In a 2010 New York Times article Verlinde already stated: gravity is an illusion. His theory goes beyond the concept of gravity as envisioned by both Isaac Newton and Albert Einstein. It will be very interesting to see other scientists sink their teeth into this.
Abstract of his article:
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional 'dark' gravitational force describing the 'elastic' response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton's constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional 'dark gravity force' explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
Heck, I'm not even going to pretend I grok any of this: I shine shoes for a living and just hope that my understanding of gravity-as-we-know-it is sufficient to catch the coins customers drop into my weary hand.
(Score: 0, Troll) by Anonymous Coward on Wednesday March 01 2017, @05:38PM (33 children)
"Gravity", as in "an inherent property of mass" has never, ever been proven.
Ever.-
Look it up, it has not. Nowhere, EVER, has it ever been demonstrated that mass attracts mass because it is mass and not because of some other factor messing it up (like electricity). NE - VER. Never! Not from Cavendish, nor from Newton, neither from those Italian dudes in 'Nature' 2015. Not once, nil, zero, nada. Please keep that in mind, and behave in a civilized fashion when engaged in relevant conversation.
(just a heads-up so you guys know your shit n avoid embarrassment if you ever find yourselves in the position of defending `Gravity')
(Score: 0) by Anonymous Coward on Wednesday March 01 2017, @05:46PM
I wish Le Sage gravity got more attention today, in attempts to address the shortcomings:
https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitation [wikipedia.org]
(Score: 0) by Anonymous Coward on Wednesday March 01 2017, @05:55PM
Calm down, it's going to be alright :)
(Score: 2, Informative) by Anonymous Coward on Wednesday March 01 2017, @06:05PM
No physical theory is "proven", and you could take your own advice about civilized discussion.
(Score: 4, Informative) by FatPhil on Wednesday March 01 2017, @06:10PM (17 children)
Actual proof, as a philosophical/mathematical concept, is *unrelated* to the "extremely unlikely to be wrong given our current knowledge" use of the term that the physical sciences have to put up with.
If you are confusing the two, then that shows a weakness in your own mind. If you think that scientists are confusing the two, then you are either listening to woo-woo "scientists", which demonstrates a weakness in your ability to select who to believe on such matters, or you are misinterpreting what those scientists are saying, which is simply again a weakness in your own mind.
Now go read some Popper, you're nearly a century behind the educated world. Actually, read some Hume first, as we need to get you out of short trousers first.
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 1, Interesting) by Anonymous Coward on Wednesday March 01 2017, @06:24PM (4 children)
I think Popper is pretty much debunked and Lakatos is the current king of philosophy of science. Basically science is about making surprising a priori predictions (that turn out to be accurate) and coming up with the least byzantine set of ad hoc explanations for the deviations from these predictions.
(Score: 2) by HiThere on Thursday March 02 2017, @12:40AM (1 child)
Popper hasn't, and can't be "debunked". You can argue with how he uses words, or whether his domains are properly specified..and at times I would, but this is far from being debunked. That's like saying Newton was debunked. I'll admit I've never read Lakatos, but you can be pretty sure that he, also, did not say the last word on the subject. He may cover a wider field than does Popper (who really only properly covers experimental sciences that have readily replicated experiments).
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 0) by Anonymous Coward on Thursday March 02 2017, @03:20AM
Falsifiability doesn't work as a criterion. The only reason it seemed to work is because scientists before that knew what they were doing and predicted something precise. Now we have NHST where everyone tries to predict whether A is correlated with B (the vaguest thing possible). That aint science, because an insane number of explanations can be easily put forward for such vague observations. Such predictions, and "tests" of them, do not help distinguish between the theories.
As lakatos put it, every theory grows in a "sea of anomalies". They are born and live falsified. It is all about making one/few precise predictions that otherwise have low prior probability.
(Score: 1) by khallow on Thursday March 02 2017, @12:51PM (1 child)
I think Popper is pretty much debunked and Lakatos is the current king of philosophy of science.
First, this is an inappropriate use of the term, "debunk". Disagreement or elaboration is not "debunking". This seems particularly common in the debate over climate change where once someone disagrees with another, it becomes a "debunk" followed by the rhetorical dismissal of the prior opinion or claim. I disagree with you, therefore I have "debunked" you and can ignore whatever it was you said. I hope readers understand the problems with that approach.
Because that leads to the second observation. From what I've read, Lakatos isn't really disagreeing on Popper's approach except to say that it tends to be too aggressive in falsification, discarding models too quickly.
Basically science is about making surprising a priori predictions (that turn out to be accurate) and coming up with the least byzantine set of ad hoc explanations for the deviations from these predictions.
Notice what this sentence says. First, what is an a priori prediction which is both surprising and accurate? It's an observed falsification of the current model. That's definitely a standard Popper-style approach right there. And coming up with the "least byzantine set" of ad hoc explanations? Well, that's coming up with a new model using a vague and subjective criteria. I think there could be some room for improvement there. In actual science, there would be multiple creations of not necessarily ad hoc (models can often be reused, for example, in different fields and so may not be created for that purpose but rather a different one) models selected for a variety of subjective criteria followed by more observation and so on.
So we have a Popper-style model falsification approach combined with a perhaps peculiarly human approach to generating additional models with what I see as some modest room for improvement in the description of the process. That's not much of a deviation from Popper and thus, not much of a debunking.
(Score: 0) by Anonymous Coward on Thursday March 02 2017, @03:12PM
Well, there is Popper0, Popper1, and Popper2. Popper0 is the naive falsificationism that lay people (eg statisticians) think Popper described, Popper1 is Popper, and Popper2 is how Lakatos refers to his own ideas.
(Score: 0) by Anonymous Coward on Thursday March 02 2017, @12:17AM (11 children)
"Now go read some [..] as we need to get you out of short trousers first."
How thoughtful, I ll take that under consideration. Now, if you are done with your childish nonsense and laughable patronizing attempts, please direct your attention here as I got something special for you too: it is called a free-falling spring, and will help you understand how you have been meticulously deluding yourself into believing that 'expanding the mind' means 'quoting shit others said or wrote'.
The challenge is simple: a spring of length x and stiffness k is hanging at rest inside a gravity field g, and is released. Describe (math model) the motion of this free-falling spring.
Good Luck (you are going to need it)
(Score: 2) by HiThere on Thursday March 02 2017, @12:45AM (7 children)
That's a very simple problem. You just model the "free falling spring", and stop before it collides with anything. Of course, the shape of the spring, and how it's rotating will introduce a few complexities even before the first collision. ... When, among other things, you need to start considering the elasticity of to two surfaces (as well as the reaction of the rest of the spring). So stop first.
A fairer example would be considering how the air moves past the blades of a rotating fan. There are lots of places you can look things about that up without needing to rent time on a supercomputer.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 0) by Anonymous Coward on Thursday March 02 2017, @01:22AM (6 children)
That's a very simple problem.
Oh really? Solve it then, and report back with your solution.
Or don't, and just keep believing you know "how simple" it is.
(Score: 1) by khallow on Thursday March 02 2017, @12:57PM (5 children)
Oh really? Solve it then, and report back with your solution.
The other poster already did.
(Score: 0) by Anonymous Coward on Friday March 03 2017, @12:08PM (4 children)
The other poster already did.
Hi khallow, no, he did not, perhaps my fault for not explaining the problem better. I welcome you to give it a go: a spring of mass m and stiffness k is at rest hanging vertically inside a gravitational field g and is released. The question is to derive the equation of motion for the bottom tip of the spring as a function of the vertical distance from the ground against time, from the moment the spring is released to the moment it contacts the ground, and the answer is to be expressed this in terms of m, k and g, or any other parameter pleases you as long as you formulate it in math (differentials, a polynomial or a plot are all good) as long as you can justify your derivation.
(Score: 1) by khallow on Friday March 03 2017, @03:08PM (3 children)
Hi khallow, no, he did not, perhaps my fault for not explaining the problem better. I welcome you to give it a go: a spring of mass m and stiffness k is at rest hanging vertically inside a gravitational field g and is released. The question is to derive the equation of motion for the bottom tip of the spring as a function of the vertical distance from the ground against time, from the moment the spring is released to the moment it contacts the ground, and the answer is to be expressed this in terms of m, k and g, or any other parameter pleases you as long as you formulate it in math (differentials, a polynomial or a plot are all good) as long as you can justify your derivation.
You should have said that in your original demand. But even so, the process for deriving the solution was laid out. But having said that, I'd use the Lagrange approach:
L = K - V.
Here, K and V are the kinetic and potential energy of the spring. There are a variety of possibilities depending on how the mass and potential energy are distributed. In general, you can always find a solution computationally, even with complex three dimensional dynamics or if the spring can break or other sort of "memory" (where the current behavior of the spring depends on what happened to it in the past).
But let's suppose the simplest case where the mass of the frictionless spring is all concentrated in a single point with height x - larger means higher, the potential energy of the spring follows Hooke's law, and the gravitational field is constant. Then
K = 1/2 mv^2 (v = dx/dt, m is the constant mass of the spring concentrated at point x) and
V = 1/2 k(x_0 - x)^2 + mgx where k is a stiffness coefficient (not necessarily your stiffness coefficient, g is the acceleration due to the gravity field). The potential energy of the spring is just the sum of the potential energy of the spring and the potential energy of the mass in the gravitational field.
The key trick to using the Lagrangian L is that the partial derivative of L with respect to x is equal to the normal derivative with respect to time of the partial derivative of L with respect to v = dx/dt. Hmmm, let's call it
\dee L/ \dee x = d/dt( \dee L/ \dee v).
Then
k(x - x_0) + mg = m dv/dt.
Still looks pretty simple to me.
(Score: 0) by Anonymous Coward on Friday March 03 2017, @05:12PM (2 children)
The question is for the bottom of the spring, so the spring has to be considered at least as a one-dimensional 'physical' object; no point masses.
k(x - x_0) + mg = m dv/dt.
Again, it is the bottom of the spring that is concerned as a function of time: does x here represent the bottom of the spring?
(Score: 1) by khallow on Friday March 03 2017, @06:34PM (1 child)
The question is for the bottom of the spring, so the spring has to be considered at least as a one-dimensional 'physical' object; no point masses.
If you're assuming that the mass distribution is distributed along the spring, then we'll have to do something different. Let's suppose uniform distribution of mass. x(a) (actually x(a) := x(a;t)) is the position of the spring where fraction a mass is on one side (as parameterized by the coefficient a) at given time t. Overlapping of the spring is allowed. Kinetic energy and the potential energy due to gravity do not change much:
K = 1/2 m integral{a=0 to 1} dx(a)/dt da, and
P_{grav} = mg integral {a=0 to 1} x(a) da.
The potential energy due to the spring is now proportional along the length of the spring to the square of change in parameter a from a default rest state spring with no force acting on it. P_{spring} = 1/2 k integral{a=0 to 1} (dx(A)/da - b)^2 da. And fix the initial parameters of the spring (x(a; t=0). b happens to be the at rest length of the spring without tension (so b is your "x"). Now, we have a variational equation. We still can use the Lagrangian:
d/dt \delta L/ \delta (dx(a)/dt) = \delta L / \delta x(a). Solving the math becomes either a matter of a computer model, or getting all your integrals in terms of the variation of x(a), not various derivatives of the variation of x(a) (there's a second derivative of time t, which needs to be reexpressed in terms of a Kronecker delta function, and a first derivative of parameter a, which can be transformed via some integration by parts manipulation, as integrals of some function of x(a) and its derivatives collectively times a single counter-factor, the variation of x. The first factor thus has to be identically zero resulting in a differential equation. I feel there's little point to going that far though. Notice that while there is a lot of it, the math has come through via a variety of simple rules.
And as HiThere noted, once you have the model, you just use the model to compute the position of the spring. That remains simple as expected. Once we have the basic equation of motion, we can then add other effects such as your interaction with a solid surface, internal friction of the spring, etc. While that may look very hard from our very limited viewpoint it doesn't actually change the computational complexity of the problem that much.
(Score: 0) by Anonymous Coward on Friday March 03 2017, @07:37PM
If you're assuming that the mass distribution is distributed along the spring
I am,
And as HiThere noted, once you have the model, you just use the model to compute the position of the spring.
No dispute there: only I do not have such a model, and it is not trivial to produce. Your honest analysis may change that, so I guess I can treat it as homework, implement a model and see what happens.
(Score: 2) by FatPhil on Thursday March 02 2017, @10:27AM (2 children)
Why are you asking a pure mathematician an applied maths question? How will that help you grasp metaphysics?
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 1) by curril on Thursday March 02 2017, @11:20PM
Sorry, that's not correct. The instant the spring is released, the top the spring will start moving down, releasing tension and the bottom of the spring will start falling (albeit slower than the top). The center of mass of the spring will fall strictly by the acceleration of gravity g at that point, while the ends of the spring will oscillate about the center of mass according to Hook's Law and simple harmonic oscillation. Of course, if the length of the spring is such that g can't be assumed to the same at the ends of the spring, then spring will also experience tidal forces that change the frequency of oscillation over time.
(Score: 0) by Anonymous Coward on Friday March 03 2017, @12:38PM
was under gravity/tension equilibrium before it was dropped, and therefore remains stationary until the tension disappears [..] where the neutral extension is totally collapsed, the spring will simply collapse, base unmoving
Are you proclaiming the slingy a special case spring that exactly cancels out it stiffness with gravity so its bottom always stays put until the top collapses, even when its mass or stiffness is messed with? If so, please math it up (express it as a function of time)
Why are you asking a pure mathematician an applied maths question?
Sorry, you lost me: who is the applied mathematician?
How will that help you grasp metaphysics?
Where did that one come from? Would you mind if we settle the math part of the discussion first?
(Score: 1, Insightful) by Anonymous Coward on Wednesday March 01 2017, @06:44PM (9 children)
Is this more electric universe crap?
"Magnetism", as in "an inherent property of mass" has never, ever been proven.
Ever.-
Look it up, it has not. Nowhere, EVER, has it ever been demonstrated that charge attracts charge because it is electromagnetic and not because of some other factor messing it up (like gravity). NE - VER. Never! Not from Maxwell, nor from Faraday, neither from those Italian dudes in 'Nature' 2015. Not once, nil, zero, nada. Please keep that in mind, and behave in a civilized fashion when engaged in relevant conversation.
(just a heads-up so you guys know your shit n avoid embarrassment if you ever find yourselves in the position of defending `Magnetism')
Fuckin' magnets. How do they work?
(Score: 1) by khallow on Thursday March 02 2017, @01:16PM (8 children)
Is this more electric universe crap?
Or it could be our resident flat Earther rearing [soylentnews.org] to strike. A NASA/Freemason conspiracy to fake the Moon landing for Satan is more real than gravity.
(Score: 0) by Anonymous Coward on Friday March 03 2017, @01:16PM (7 children)
Or it could be our resident flat Earther
'flat Earther' in lack of a better description, yes- I like this forum a lot. I could open an account I guess and observe to what amount 'flamebait' and 'troll' is a reflex to my posts, whether I have ever spread enough hate, fear and division to actually deserve those designations, and what sorts of AC flak I ll be receiving, assuming I don't get straight out banned from the start and can get an account in the first place.
(Score: 1) by khallow on Friday March 03 2017, @03:23PM (6 children)
"Gravity", as in "an inherent property of mass" has never, ever been proven.
We have yet to observe mass that doesn't have gravity of the appropriate extent for the mass. So sure, it looks like an inherent property which is the point of empiricism, looking at things to determine their properties.
Nowhere, EVER, has it ever been demonstrated that mass attracts mass because it is mass and not because of some other factor messing it up (like electricity).
And there's a fair number of theories that propose that there's really just one force, it just decomposes nicely into four pieces in our situation.
whether I have ever spread enough hate, fear and division to actually deserve those designations
Don't forget ignorance which is a key attribute of your posts. Let's throw out three considerations:
1) If Earth is not a round ball-like object, then how is it shaped?
2) Why isn't the Earth uniformly lit or dark?
3) Why is the shadow of Earth when cast on the Moon, always round?
(Score: 0) by Anonymous Coward on Friday March 03 2017, @04:26PM (3 children)
Different AC here. These questions are actually key to calculating the size of the 33 C greenhouse effect:
1) A concave disk facing the sun.
2) It is uniformly lit, thus the concavity.
3) The earth is disc-shaped.
This is all climate science 101. http://www.atmos.washington.edu/~davidc/ATMS211/articles_optional/Hansen81_CO2_Impact.pdf [washington.edu]
(Score: 1) by khallow on Friday March 03 2017, @06:41PM (2 children)
These questions are actually key to calculating the size of the 33 C greenhouse effect:
Just like assuming for a physics problem that cows are spherical and frictionless makes them so? The paper you linked provides zero support for your assertion. Even worse for the Earth, it used a one-dimensional model not the conditions you asserted. That must have hurt.
(Score: 0) by Anonymous Coward on Friday March 03 2017, @07:16PM (1 child)
How does a one dimensional object have a radius?
(Score: 1) by khallow on Friday March 03 2017, @07:45PM
How does a one dimensional object have a radius?
I can think of a variety of ways it could and couldn't be done. Every one of them is irrelevant to this discussion.
(Score: 0) by Anonymous Coward on Friday March 03 2017, @08:09PM (1 child)
I guess I called it then, eh?
Yes,
We have yet to observe mass that doesn't have gravity of the appropriate extent for the mass.
You speak as if you already know for a fact that mass gravitates, and you are expecting to falsify that by observing mass that doesn't. I have never observed mass that gravitates, either within or outside of 'established parameters' (big G). Where have you observed mass to gravitate, and how?
1) If Earth is not a round ball-like object, then how is it shaped?
According to a testimony of the first man to see it from the stratosphere, Auguste Piccard, it looks like a dish with an upturned surface, horizon at eye level. He did not manage to see the whole Earth.
2) Why isn't the Earth uniformly lit or dark?
Water is transparent, why can't you see the bottom of the ocean?
3) Why is the shadow of Earth when cast on the Moon, always round?
I pay attention to such predicted events and have seen the moon get dark in different ways. If you want to claim that what darkens a globular moon is the shadow of a globular Earth cast on it I must tell you that I see inconsistencies with that idea. Eclipses differ a lot. So it is more efficient if you refer to eclipses per eclipse, as they are becoming more and more documented and are easy to refer to.
Having said that, at which eclipse did you observe the shadow of the Earth being round and cast on the moon?
(Score: 1) by khallow on Friday March 03 2017, @09:12PM
You speak as if you already know for a fact that mass gravitates, and you are expecting to falsify that by observing mass that doesn't. I have never observed mass that gravitates, either within or outside of 'established parameters' (big G). Where have you observed mass to gravitate, and how?
I have observed 5-10 kg masses gravitate. I used a similar setup to the Cavendish experiment [wikipedia.org] in a college physics lab. One pair of the heavy weights swung freely from a tether suspended from the ceiling. The other pair, which was placed very closed to the first could be swung on a pivot in the same axis as the tether so that second pair was just a little offset rotationally of the first pair in the circle of rotation, either clockwise or counterclockwise. That is, the weights of the free-swinging beam could be pulled clockwise or counterclockwise by the second beam which allowed one to pivot between the two modes. One significant deviation was to attach a mirror to the wire of the oscillating masses and project a laser beam down a fairly long hallway to get a very accurate measure of the deflection of the beam.
So for example, you could wait till all oscillation had ceased, then pivot the second pair of weights so that their pulled on the first pair in the opposite direction and measure over time the deflection of the tether's rotation at the other end of the hallway. This gave you both the net deflection and as in the original Cavendish experiment, the period of oscillation of the tether gave you an estimate of the stiffness of the tether as a spring. The combination allowed you to estimate the net force change acting on the free swinging weights. Then from estimates of the distance between the weights and how gravity acts between non-point masses, my estimate was within 20% of the measured force acting on the weights. That's pretty good for an undergrad lab.
According to a testimony of the first man to see it from the stratosphere, Auguste Piccard, it looks like a dish with an upturned surface, horizon at eye level. He did not manage to see the whole Earth.
If it is dish-shaped, then where is the edge of the dish? If there is no edge, then that both strongly restricts what sort of shape the Earth can be (I'll note here that the Earth is finite in extent, that plus no holes means the Earth would be topologically equivalent to a sphere, that still allows for some weird shapes, but maps could still be projected without loss or overlap onto a globe) and leads to the question of why would there be large dimples?
Water is transparent, why can't you see the bottom of the ocean?
Because water is opaque on the scale of kilometers. The Sun doesn't significant change in size as it moves across the sky and we see it move below the horizon from our point of view - so there isn't a lot of moving back and forth and hence, opportunity for the Sun's light to be obscured from my position). Further, anyone with a cell phone can verify, by calling people elsewhere in the world, that the Sun is in a different position in a consistent way. For example, until the end of my season this week, I worked at Yellowstone National Park. At one point, a coworker had called a significant other with video who was currently residing in the Philippines, I believe around 9pm Mountain time. The real time image clearly showed the significant other in daylight, even though Yellowstone had been in darkness for some time.
So the shape of Earth has to be something that allows the Sun to shine on parts of the Earth while not shining on other parts of the Earth in a very predictable and consistent way, day after day.
I pay attention to such predicted events and have seen the moon get dark in different ways. If you want to claim that what darkens a globular moon is the shadow of a globular Earth cast on it I must tell you that I see inconsistencies with that idea. Eclipses differ a lot. So it is more efficient if you refer to eclipses per eclipse, as they are becoming more and more documented and are easy to refer to.
I don't. I too make a fair bit of such observations and the umbral shadow is consistently very circular. For examples, the September 16, 2016 lunar eclipse which turned out quite nice from Yellowstone and a 1993 or 1994 lunar eclipse which I observed from western North Carolina. I recall it as being a partial eclipse only which would make it the May 25, 1994 one. It's also worth noting the predictability of these events which can be predicted decades out (well actually much further out than that, but who would wait for an eclipse millennia from now?).
(Score: 4, Funny) by maxwell demon on Wednesday March 01 2017, @08:14PM
Yeah, intelligent falling is the only reasonable explanation.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 1, Informative) by Anonymous Coward on Wednesday March 01 2017, @08:27PM
Wording suggestion: "Gravity is an observed phenomenon that follows a known simple model on a smaller scale, but not on a larger, galactic scale."
This doesn't require explaining or giving the mechanism of gravity. It's described merely as an observed pattern in nature.
And, I use "known" because perhaps there is a simple model that works on ALL observable scales, but we simple haven't found/devised it yet.
(Score: 0) by Anonymous Coward on Wednesday March 01 2017, @05:39PM (34 children)
If we were actually figuring things out, the universe would be getting simpler and more comprehensible. Instead you need to dig through denser and denser math to figure out what they are talking about, with more and more bizarre interpretations.
(Score: 1, Insightful) by Anonymous Coward on Wednesday March 01 2017, @05:54PM (8 children)
That increasing body of mathematics is what comprehensibility looks like.
What you are actually experiencing is not an increasing incomprehensibility, but rather an improving perception of your own incompetence.
(Score: 0) by Anonymous Coward on Wednesday March 01 2017, @06:04PM (7 children)
I don't think it has to do with my incompetance. I mean no one actually uses GR or QM for anything practical because the calculations are too hard, with little benefit to show for it. Unless you mean the incompetence of humanity in general?
(Score: 0) by Anonymous Coward on Wednesday March 01 2017, @06:21PM (6 children)
For instance, GPS wouldn't work without an understanding of general relativity.
(Score: 0) by Anonymous Coward on Wednesday March 01 2017, @06:28PM (5 children)
GPS doesn't use GR. These use a post-Newtonian approximation (ie calculate the Newtonian result, then add some correction factor). Without GR, people would just add some other correction factor that approximates the correct result. No one uses GR for anything practical because it is too difficult to deal with.
(Score: 0) by Anonymous Coward on Wednesday March 01 2017, @06:43PM (1 child)
"It isn't GR... it's an approximation of GR!"
What?! Any student of Newtonian mechanics will tell you that half the solutions involve making "simplifying" approximations of the underlying problem; I guess nobody uses even Newtonian mechanics for anything practical. Bish, please.
(Score: 0) by Anonymous Coward on Wednesday March 01 2017, @06:55PM
Usually this is stuff like "treat the earth like a sphere" though. Not changing the fundamental assumptions (speed of gravity doesn't change between instantaneous to the speed of light, etc). You will still see some form of F = G*m1*m2/r^2 because what is to simplify? Ok, they use GM* since that is closer to what can be measured, but that is not equivalent.
*https://en.wikipedia.org/wiki/Standard_gravitational_parameter
(Score: 1) by khallow on Friday March 03 2017, @03:32PM (2 children)
These use a post-Newtonian approximation
Which readily comes from GR. As you note, they could needed some other approximation, but they would need to justify the correction, if they did so. And that would mean coming up with a model that wasn't current GR.
You see this with a variety of complex equations. Two common examples are the Navier-Stokes equations and the corresponding equations for magnetohydrodynamics (plasma fluid dynamics). The two equations are bulky (and fundamentally broken at the subatomic level, which sometimes can bite you at far larger spatial scales) so they routinely use approximations where various terms of the equations are set to zero rather than merely be very small.
(Score: 0) by Anonymous Coward on Friday March 03 2017, @04:59PM (1 child)
(Score: 1) by khallow on Friday March 03 2017, @07:48PM
But was there a pre-existing extremely simple model that was 99.99% correct in those cases?
What does 99.99% correct mean?
(Score: 4, Touché) by sgleysti on Wednesday March 01 2017, @06:21PM (20 children)
What makes you think the universe should be easily comprehensible to human beings?
(Score: 1, Funny) by Anonymous Coward on Wednesday March 01 2017, @07:07PM
A cosmetologist adviser to Trump told me it was true.
(Score: 0) by Anonymous Coward on Wednesday March 01 2017, @07:17PM (18 children)
Because that is the whole principle behind science, which has been very successful? Cultures that deviate from that get wiped out by those who stick to it.
It is really amazing how quickly people want to jump back into theology just to keep believing what they were taught in school. It requires constant vigilance to stay on the right track.
(Score: 2, Disagree) by sgleysti on Wednesday March 01 2017, @08:07PM (8 children)
I believe that constructive empiricism
https://en.wikipedia.org/wiki/Constructive_empiricism/ [wikipedia.org]
https://plato.stanford.edu/entries/constructive-empiricism/ [stanford.edu]
is a good philosophical description of how science operates. Scientists construct theories about how the universe operates, and the goal is to adequately describe empirically observable reality. Acceptance of a scientific theory only extends to those parts of it which affect observable entities.
This is a far cry from theology, which is primarily human speculation about unobservable entities.
(Score: 2, Disagree) by Grishnakh on Wednesday March 01 2017, @09:53PM (7 children)
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.
(Score: 2, Disagree) by HiThere on Thursday March 02 2017, @12:52AM (6 children)
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.
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(Score: 3, Insightful) by Grishnakh on Thursday March 02 2017, @02:08AM (5 children)
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)
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)
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)
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)
"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
"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.
(Score: 1, Insightful) by Anonymous Coward on Wednesday March 01 2017, @08:09PM (6 children)
No, the whole principle behind science is to make observations and construct models to try to understand the workings of physical law. Simplicity is not a requirement; it is a desirement. It is more a philosophically driven attitude than anything else. Given two models where one has symmetric central forces and mathematically beautiful equations, and one that is teetering on stability where you have large offsetting terms barely holding together numerical stability, you go with the first one. Why? A belief that Nature is governed by simple and/or beautiful laws is a big reason, but that is more a philosophical stance than anything else. Plus, history has also shown that large, complicated models break down or become too burdensome (e.g., epicycles), and aren't able to make future predictions.
Back on point, the fact that one cannot understand the mathematics behind something does not imply that something is wrong. Mathematics, and higher level mathematics can be quite beautiful to those who understand it. A lot of string theory work is like that. Forcing your models of physical law to conform to the requirement that they must be expressed at a high school calculus level is what I would consider a theological approach to bend nature to your understanding and not the other way around.
(Score: 0, Disagree) by Anonymous Coward on Wednesday March 01 2017, @08:42PM (1 child)
If you believe the universe is incomprehensible then this effort is misguided.
It isn't a matter of understanding, it is a matter of time/effort. As mentioned, just running a computer program that does the calculations (w/o any understanding) is not something that is done because the model is so damn complicated.
(Score: 3, Informative) by tangomargarine on Wednesday March 01 2017, @09:02PM
If you believe the universe is incomprehensible then this effort is misguided.
He didn't say that.
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by HiThere on Thursday March 02 2017, @12:56AM
The very concept of "physical law" is a problem. If you had said "observed regularity" I'd have no problem, but the concept of law involves an implicit assumption that "this is the truth, the whole truth, and nothing but the truth", which is probably impossible, and which I have certainly never seen.
Science is about modeling observed regularities in a way that allows accurate predictions to almost always be made. (When the predictions aren't accurate, you try to refine the model.)
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(Score: 1, Flamebait) by aristarchus on Thursday March 02 2017, @07:09AM (2 children)
it is a desirement. It is more a philosophically driven attitude than anything else. Given two models where one has symmetric central forces and mathematically beautiful equations, and one that is teetering on stability where you have large offsetting terms barely holding together numerical stability, you go with the first one. Why? A belief that Nature is governed by simple and/or beautiful laws is a big reason, but that is more a philosophical stance than anything else.
It is called "Ockham's Razor", and it will cut you bad, unless you have an alternative? The most unstable, unlikely, crazy theory is more likely to be the correct one? We call that the "jmorris razor", followed by the "khallow correlary", and further backed up by "Runaway1956". It's just "Runaway", he is a force of confusion all by hisself, without being a razor, a law, or even a corrolary. No, Ockham's razor has stood the test of time, in the face of all the crazy, and was even cited by Jodie Foster in "Contact", co-written by Carl Sagan.
(Score: 1) by khallow on Friday March 03 2017, @03:35PM (1 child)
(Score: 2) by aristarchus on Friday March 03 2017, @04:34PM
I disagree with *your* overly simplistic opinion about my comment!
(Score: 2) by maxwell demon on Thursday March 02 2017, @08:35AM (1 child)
To quote Einstein, emphasis by me:
If the universe is complex, our theories of it need to be, too. And the universe surely has to be sufficiently complicated to support life, or else we could not be there.
The universe is not constructed for us to understand. Rather, out brain has evolved to understand certain aspects of the universe that are important for survival. That this brain can go far beyond that is amazing. But we need tools for this, because our brain is not made for it. Basically, mathematics is for natural science what the airplane is for flying. We need it because we are not naturally equipped to manage the task using only our native abilities.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 1) by khallow on Friday March 03 2017, @05:43PM
Basically, mathematics is for natural science what the airplane is for flying.
The airplane is necessary for us to fly. That it works is a feature of reality. The math exists independent of our need for it. Our description of math is peculiar to us, the math itself is not.
(Score: 2) by DeathMonkey on Wednesday March 01 2017, @06:37PM
If we were actually figuring things out, the universe would be getting simpler and more comprehensible.
Why?
The Universe actually being pretty damn complicated is a hypothesis that fits the current observational data, as well.
(Score: 3, Insightful) by weeds on Wednesday March 01 2017, @09:41PM
The universe is under no obligation to make sense to you.
- Neil deGrasse Tyson
Get money out of politics! [mayday.us]
(Score: 2) by HiThere on Thursday March 02 2017, @12:47AM
Sorry, but that's not quite right. Figuring things out EITHER makes the description simpler OR lets you do more with the model. Sometimes it lets both things happen, but you sure can't count on it.
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(Score: 2) by urza9814 on Thursday March 02 2017, @06:33PM
It's all about layers of abstraction. Which most of us here on Soylent ought to understand pretty well... :)
Every scientist is like a Java developer. They just can't help it, that's the world they were born into. Humans are big (at subatomic scales...) and incapable of interpreting every single movement of every single particle. So we use higher level abstractions without even realizing it.
Now take that Java developer, and task him with understanding how a computer works. We'll be a bit nicer to the developer than the universe is to these scientists -- we'll give him a full schematic of every single transistor in the CPU and on the motherboard. And every bit of the terrabyte hard drive, and every bit burned into EPROMs and whatever else. If that PC contains nothing but a fresh install of Linux, how long do you think it's going to take that Java developer to trace every single path of every single bit to draw enough pixels to the screen to read the boot splash screen? The individual components are simple and well understood, but figuring out how they work in a combined system is a whole different challenge.
We've been building electronic computers for what, a century? And the universe has been building its abstraction layers for how many billions of years? Of course it doesn't always make sense to us, just like the idea of manual memory management won't initially make much sense to a Java developer who's used to having garbage collection.
(Score: 2) by Justin Case on Wednesday March 01 2017, @05:40PM (2 children)
There is no gravity; the Earth sucks.
There is no dark matter; black holes suck anything and they like it!
(Score: 1, Funny) by Anonymous Coward on Wednesday March 01 2017, @06:44PM (1 child)
There is no gravity; the Earth sucks.
If that was how it worked, the universe would revolve around your mom.
:D
(Score: 2) by Justin Case on Wednesday March 01 2017, @07:59PM
If that was how it worked, the universe would revolve around your mom.
I never had a mom, you insensitive clod!
(Score: 2, Insightful) by WillR on Wednesday March 01 2017, @07:49PM (1 child)
Department of Astrophysics Motto: Yes, everyone has already had the idea 'Maybe there's no dark matter - gravity just works differently on large scales!' It sounds good but doesn't really fit the data.
(Score: 2) by HiThere on Thursday March 02 2017, @01:06AM
Sorry, but this guy's theory *does* seem to fit the data. Perhaps better than the "dark matter" idea...which, remember, nobody has ever directly detected. They've seen certain effects. If this idea ALSO predicts those effects, but doesn't depend on particles that we can't find, then it may be a better idea.
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(Score: 5, Informative) by Gaaark on Wednesday March 01 2017, @10:02PM (9 children)
Mike McCulloch at
http://physicsfromtheedge.blogspot.ca/2016/11/critique-of-verlindes-gravity-1.html [blogspot.ca]
has a nice 'debunking' of Verlinde, in that some of his theory is just more "dark matter"
1) Emergent gravity predicts an anomalous effect that occurs only on large scales, and so it is falsified by the many tiny globular clusters and small satellite galaxies that show even more of an anomalous rotation effect than big galaxies (MiHsC is successful with these minnows too because it predicts anomalies at low accelerations, instead of just large scales). Emergent Gravity also cannot deal with many other anomalies like the cosmic acceleration, the flybys and the emdrive. MiHsC explains all of these.
2) Emergent Gravity has been falsified by experiments in which uncharged neutrons were confined in the vertical direction by making them bounce off a mirror below, and allowing gravity to pull them down. It was found that, in agreement with quantum mechanics, the neutrons did not move continuously along the vertical direction, but jumped from height to height like mountain goats. Entropic gravity predicts the wrong heights (see the Kobakhidze reference).
3) Emergent Gravity relies on something called code subspace, which is something we cannot directly see, so it is another kind of informational dark matter that is difficult to test for directly.
More imaginary stuff in order to dispel imaginary stuff: might as well include the (what number are we at now... 13? 24? 26?) imaginary dimensions that MAKE STRING THEORY WORK!!
HEY! STRING THEORY WORKS LIKE THIS: ONE PLUS ONE, PLUS 24 IMAGINARY DIMENSIONS = 3000 JILLION AND 48!!!! SEE IT IS SO EASY!!!!
Car analogy: my car runs on gas, oil and an electric spark and it does this successfully because of the 26 imaginary dimensions of space!!!! They are there, oh yes, they are there. How do we know???? THE CAR FECKING RUNS, DOESN'T IT?!?! DOESN'T IT!!!!!???????!!!!!! SEEEEEEEEE!!!! CAN YOU SEEEE!!!!!
At least Mike Mculloch's theory has some possible backup findings:
UNRUH radiation confirmed? http://physicsfromtheedge.blogspot.co.uk/2016/09/unruh-radiation-confirmed.html [blogspot.co.uk]
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 2) by HiThere on Thursday March 02 2017, @01:18AM (7 children)
Yeah, he doesn't like it. But he admits that he didn't really read the paper, but skimmed most of it. As a result, I can't really take his criticisms that seriously. They might be right, or he might have skipped over places that explained them. He does have some valid reasons for his skepticism, but they may not hold up. Or, of course, they may.
To pick one, what about globular clusters? Does the proposed theory actually break down there, or is it just something he didn't read? Or perhaps it's a place that the math needs to be developed for? To me it appears that all three are possible, and I don't have the math to follow it myself. (I may never have had the math.)
The problem is, if particulate dark matter is the correct theory, then why can't we detect it directly, rather than through indirect evidence, like galaxy rotational speeds. There have bee a huge number of theories about what dark matter was, but so far none of them have shown up when searched for. By now I'm quite willing to accept the idea that it's something quite a bit different than the simple models.
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(Score: 4, Interesting) by stormwyrm on Thursday March 02 2017, @03:25AM (4 children)
If you had a particle that only interacts by the weak interaction and gravity, or worse yet, via gravity alone, as some cold dark matter candidates postulated are, then you’ll really have a hell of a time trying to detect them, whatever they are, as these forces are the weakest of the lot by a very wide margin. Relative to the electromagnetic interaction, the weak interaction is some eleven orders of magnitude weaker, and gravity some 36 orders of magnitude weaker. That’s the trouble here.
However, we do have examples of particles in the Standard Model that, like dark matter, can interact only via the weak interaction and gravity: the various types of neutrinos, and the work on neutrinos gives some idea of the difficulties involved in trying to detect dark matter. The neutrino was hypothesised as an explanation for the missing energy in beta decay events, and it took several decades from when Wolfgang Pauli first hypothesised them as “a desperate remedy”, to their unambiguous direct detection. Even today, we can still detect only fairly high energy neutrinos. The low energy neutrinos, such as those in the cosmic neutrino background, are still resistant to all attempts at direct detection, though there is indirect evidence for them. We can expect that dark matter will be similarly difficult to directly detect barring some new breakthrough.
I will emphasise what Sabine Hossenfelder has stated in the last part of the article: the ultimate test for any alternative to the particle dark matter hypothesis is how well it holds up at galaxy cluster and cosmological scales. Wake me up when someone comes up with a modified gravity theory that can reproduce the Bullet Cluster and the CMB anisotropies. Dark matter manages to do that, so any alternative must be able to at least do the same. Galaxies and globular clusters are easy as far as that goes.
Numquam ponenda est pluralitas sine necessitate.
(Score: 2) by HiThere on Thursday March 02 2017, @08:26PM
I disagree that "ultimate test for any alternative to the particle dark matter hypothesis is how well it holds up at galaxy cluster and cosmological scales". That's certainly ONE (well, one set) of the tests it needs to pass, but it's not sufficient.
OTOH, if the theory carefully predicts a particle that there is no direct way of detecting, but passes all the other tests, then it needs to be provisionally accepted. Until some better answer comes along. But Dark Matter doesn't predict any particular particle, just that somehow there's enough invisible mass scattered in a particular distribution that could be matched by any particle having a certain broad range of characteristics. Axions, sterile neutrinos, what-all particles match the desired characteristics, but they haven't been found. This is a quite unsatisfactory situation, and since no particular particle is predicted, there's no reason to believe any particular particle is what is producing the effect. So maybe it's something else. It still needs to fit all the available evidence, but sometimes theories need a bit of fine tuning before they handle the edge cases. And sometimes the theories handle things perfectly, but it takes awhile for people to understand everything they predict. (Is the "cosmological constant" currently accepted as an appropriate adjustment? Do Black Holes have firewalls?)
This, of course, doesn't say that he's right. (Either he.) It's just that it doesn't say that he's wrong.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 2) by Gaaark on Friday March 03 2017, @02:41PM (2 children)
But the problem is is that you have to randomly ascribe dark matter to each galaxy depending on how much is needed to make the numbers work.
4 million dark matters here and it works, but you need 6.86 million dark matters here! ( All just randomly plugged in IN ORDER to make the numbers work!)
That predicts nothing.
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 2) by stormwyrm on Friday March 03 2017, @03:50PM (1 child)
And how different is that from, say, inferring the existence of a planet that you know must be there based on the observed ephemeris of a known planet, but your telescopes aren’t good enough to see? How different is that from Wolfgang Pauli hypothesising a particle that seemed at the time like it would be impossible to detect, just to make conservation of energy and momentum work for beta decay? This sort of thing is done all the time in science, in the expectation that someday observations and theories will improve to explain them better. Eventually Urbain le Verrier found Neptune, and Frederick Reines and Clyde Cowan managed to detect the neutrino. Someday, we’ll be able to really figure out what’s up with dark matter, but for now, it has the status of the neutrino before 1956 or Neptune before 1846.
And no, when you get to galaxy clusters, large-scale structure formation, and the CMB anisotropies, dark matter has plenty of predictive power. Large scale structure formation theory based on dark matter predicts that galaxy clusters ought to be forming between two and three billion years after the Big Bang, and indeed, the first galaxy cluster seen in the act of formation (CL J1001+220 [soylentnews.org]) was indeed found at between two and three billion years after the Big Bang (redshift z=2.506). Dark matter could have been easily falsified if we had seen galaxy clusters instead forming later or earlier than that. The dark matter hypothesis has also managed to correctly predict just how much hydrogen, helium, and other elements are produced in primordial nucleosynthesis. Dark matter is also inferred from peaks the cosmic microwave background power spectrum that can only come from some sort of matter that does not experience pressure when compressed. I hear a lot from modified gravity theorists about galactic rotation curves but I haven’t heard too much from them about how well their theories do with large-scale structure formation, CMB anisotropies, or galaxy cluster dynamics though. What I do hear when they try to go there, is they’re generally forced to add in stuff that looks suspiciously like dark matter. In contrast, inferring dark matter has managed to successfully fit all of the data at all these varying scales.
Numquam ponenda est pluralitas sine necessitate.
(Score: 2) by Gaaark on Friday March 03 2017, @09:18PM
And how different is that from, say, inferring the existence of a planet that you know must be there based on the observed ephemeris of a known planet, but your telescopes aren’t good enough to see?
The difference is, that it CAN'T predict the existence of the planet: you can't say "Dark matter exists because if you arbitrarily plug x+1000 dark matter into this galaxy, it perfectly matches it's 'spin'. Now this galaxy, that only works if you plug x+2001 arbitrary dark matters in."
That's like saying "Planet X exists because i burped twice yesterday". See: i arbitrarily plugged my own data into the equation and got the answer i wanted."
Galaxy size = X
dark matter needed = Y
'spin' = Z
Now if they could say "Dark matter exists because if, for a size of X you could plug in Y amount of dark matter = 'spin' of Z, therefore for a galaxy of 10 size, you plug in dark matter of 100 and you get 'spin' of 1000, you could then work out the amount of data for each galaxy and have it be predictive: so for this galaxy of size 1, you need to plug in 10 dark matter and you get 'spin' 100."
Galaxy size = X
dark matter needed = Y
'spin' = Z
....
X + Y = Z.
What they have now is "we have spin 100, so for galaxy size 1 you need to plug in 10 dark matter.... except, that doesn't always work, so you need 10 + 40 for THIS galaxy, but for this other one, size 1, you need 10 + 25" and so on".
Galaxy size = X
dark matter needed = Y
'spin' = Z
....
Z= X + Y + arbitrary amounts of Y to make it work out to be Z
NOT PREDICTIVE, therefore not a theory, but a kludge.
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 4, Informative) by Anonymous Coward on Thursday March 02 2017, @11:12AM (1 child)
So, does that mean dark matter must exist? Of course not, but:
Note that this is not string theory, but just particle physics beyond the standard model.
(Score: 0) by Anonymous Coward on Friday March 03 2017, @04:47PM
Dark matter is also predicted by neuroscience/psychology to explain consciousness and ESP.
(Score: 1) by khallow on Friday March 03 2017, @05:47PM
More imaginary stuff in order to dispel imaginary stuff: might as well include the (what number are we at now... 13? 24? 26?) imaginary dimensions that MAKE STRING THEORY WORK!!
What's imaginary about those dimensions? We do have the four forces after all which on their own naturally introduce 6 additional dimensions through force symmetries.