Has Science lost its way?

[glend (Glen)]

Originally Posted by xelasnave

Heck you would want at least $50 for each one.
So I wonder how much the grant was?
Is there a survey on how many people make their living from doing surveys.

Alex

I would be happy to count them and fill in a form if they are going to pay me. Plenty of retired people would not mind the work. They just need to send me a file. I used to process SETI data blocks on my home PC, worked in idle time, a SETI app would run all the tests on the latest data block and then send SETI a report on any abnormalities in that block for further investigation, and then i would get sent the next data block. My son ran it as well on his PC.
If they distribute the galaxy survey in that way it would not take too long.

[xelasnave]

The more I think about it the more I wonder how only 1million galaxies would indicate much at all.
I wonder how they would go about getting anything using so few.
Alex

[Stonius (Markus)]

It's early days, but this looks promising;

"A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by invoking dark matter. Prof. Erik Verlinde, renowned expert in string theory at the University of Amsterdam and the Delta Institute for Theoretical Physics, published a new research paper today in which he expands his groundbreaking views on the nature of gravity.

According to Verlinde, gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime."

http://phys.org/news/2016-11-theory-gravity-dark.html

Actual paper here;
https://arxiv.org/abs/1611.02269

Markus

Originally Posted by Stonius

I've always felt very uncomfortable with the idea of dark energy/matter. It feels a little too close to the method Theists use, interposing a preferred mechanism for things they don't understand, and then looking for the evidence that would support their beliefs (very unscientific, IMO, but what do I know?).

Okay, so the expansion of the universe is accelerating, and galaxies rotate faster than they should. Nothing wrong with saying 'We don't know why, and it could be caused by a number of factors'. But calling it dark matter/energy seems predicated on an expected result and seems particularly narrow. I'll stick my neck out and say that I don't think they'll ever find an exotic form of dark matter or energy. Far more likely that they'll discover new physics that explains it, much like a certain patent clerk did a while back.

[xelasnave]

Hi Markus
I don't like the chances of getting rid of dark matter it is now a business with many depending upon research about it and researching it enables us to use old mines that otherwise would have no other use.

An ignorant chap like myself would wonder why upon observing that rotation curves did not match the model rather than look for invisible matter rather it would seem to me that an adjustment of the model would have been appropriate.
I bet the stuff you bring gets buried.
Alex

[bojan]

Verlinde's paper from 2010
"On the Origin of Gravity and the Laws of Newton"

[sjastro]

Frankly I've lost count of the number of papers I've read over the years where dark matter can be dispensed with by modifying gravity, using GR models, holographic model etc.

Despite the issues in detecting dark matter, the phenomenological evidence is considerable.
It's interesting to draw parallels with the dark matter problem of the mid nineteen century called Neptune. The irregularities in the orbit of Uranus led some scientists to suggest that Newtonian gravity needed to be modified.

The discovery of Neptune based on the calculations of the orbital perturbations in the orbit of Uranus was a major triumph for Newtonian gravitational theory.

[xelasnave]

Originally Posted by bojan

Verlinde's paper from 2010
"On the Origin of Gravity and the Laws of Newton"

I am up to page 5 and have a feeling I am wasting my time.
Have you posted this to prove he is a great scientist or a crank.
It may be that I dont appreciate something but I would appreciate your opinion before I read any more or if indeed I should read more.

Alex

[Stonius (Markus)]

Originally Posted by xelasnave

An ignorant chap like myself would wonder why upon observing that rotation curves did not match the model rather than look for invisible matter rather it would seem to me that an adjustment of the model would have been appropriate.

And me! But according to Bojan, this is not a new train of thought, so I assume it must have been discarded for [reasons].

Will sit down to read that paper when I have a minute, but at first glance, it looks like the hypotheses are similar. There's nothing new under the sun!

Cheers

Markus

[sjastro]

Originally Posted by bojan

Verlinde's paper from 2010
"On the Origin of Gravity and the Laws of Newton"

I read this paper which seemed suspiciously familiar until it dawned on me it was discussed over a year ago in the science forum.
The concept of gravity as an entropic force has compatibility issues with basic quantum mechanics and would contradict what is observed in the double slit experiment.

Here are some of the comments made.

sjastro wrote
Hmmm.

One argument against entropic gravity is the humble double slit experiment.
If you shot neutrons at the slits the quantum wavefunction of the neutron before the measurement is made is a linear combination of the Quantum states Ia> + Ib>.
Here Ia> could mean the neutron passes through the left hand slit and Ib> the neutron passes through the right hand slit.

If you rotate the slits 90 degrees so one slit is on top of the other, the slits exist in two different gravitational potentials.
Now according to entropic gravity if the holographic screen is at some distance below the bottom slit, the number of possible microstates which is a measurement of entropy increases as one gets further away from the screen.
Hence the top slit has many more microstates than the bottom slit even if the slits are separated by only the Compton wavelength of the neutron.

The problem is these microstates need to be considered in the quantum wavefunction. The quantum wavefunction is no longer simply Ia> + Ib>.

The difference in the number of microstates between the top and bottom slits would destroy the observed interference pattern as observed in the slit experiment as the probabilities of where the neutron hits the detector behind the slits have been changed.

Steven

sjastro wrote
Experiments show the orientation of the slits doesn't effect the observed interference pattern.
Before the observation is made the neutron is in a superimposed quantum state Ia>+Ib>.
Mathematically each state Ia> and Ib> has the same dimension or contains the same number of terms for superimposition to occur.
In the case of entropic gravity the neutron passing through the higher slit has many more terms describing it's quantum state when compared to when it passes through the lower slit.
Mathematically it is not possible to form a superimposed quantum state.

The lack of a superimposed state means that quantum interference cannot occur and one would not expect to see an interference pattern if the model of entropic gravity is correct.

One can use protons, electrons, even buckyballs instead of neutrons.

Steven

sjastro wrote
Alex,

Quantum states are described using Dirac's Bra-Ket notation.

The Quantum states are mathematically handled as single column or row matrices.
A superimposed quantum state such as a neutron before it hits the detector in the double slit experiment is in the form Ia>+ Ib>.
This involves matrix addition.
For matrix addition to occur the wavefunctions Ia> and Ib> must contain the same number of matrix elements.

However as has been pointed out if entropic gravity is correct the upper slit has many more microstates than the lower slit in which case Ia> and Ib> now longer contain the same number of elements.
Matrix addition is impossible and a superimposed quantum state cannot be formed.
The familiar interference pattern observed on the detector screen caused by the collapse of the superimposed quantum state should not be observed simply because there is no superimposed state to start with.

This a mathematical argument against entropic gravity.
The issue is on the validity of whether the thermodynamic microstates themselves can form the basis of the wavefunctions.
Another argument purely from a physics perspective is the different gravitational "environments" of the lower and upper slits results in quantum decoherence which would destroy the observed interference pattern.

Steven

[xelasnave]

Thanks Steven I must confess I did not recall it.
And excellent point re Neptune.
Alex

[bojan]

Originally Posted by Stonius

...., but at first glance, it looks like the hypotheses are similar. There's nothing new under the sun!

Author is also the same

I posted this link to remind you guys (and me) that we discussed this earlier, but I forgot exactly when was it.
Steven's explanation nailed it right through.

[Stonius (Markus)]

Apologies for going over old ground. I think this must have been just before I came along :-)

-Markus

[sjastro]

Originally Posted by Stonius

Apologies for going over old ground. I think this must have been just before I came along :-)

-Markus

No need for apologies.
It's popped up on Brian Koberlein's site.
https://briankoberlein.com/2016/11/1...ce-of-gravity/

Incidentally Brian Koberlein is a real character and a very good science communicator.
Unfortunately some of his pupils have rather different opinions.
http://www.ratemyprofessors.com/Show...jsp?tid=348120

If only this rating system was available when I was at Uni..........

[madbadgalaxyman (Robert)]

Originally Posted by sjastro

Frankly I've lost count of the number of papers I've read over the years where dark matter can be dispensed with by modifying gravity, using GR models, holographic model etc.

Despite the issues in detecting dark matter, the phenomenological evidence is considerable.

Agreed!!!

I once asked a leading Dark Matter theorist , "do you really (and truly) believe in Dark matter?"

He replied that "you have to go where the data leads", as all the existing data on the space velocities of the galaxies (and their member stars) can be currently explained simply by positing the existence of large amounts of some kind of unknown gravitating matter, whether in the form of exotic particles, dust, stars, low-albedo copies of the Astrophysical Journal, or something even stranger.

There is currently no necessity for any other explanation of the kinematics and dynamics of the galaxies and their constituent stars, as so far observed by astronomers.

However, of course, the reason for the observed velocity field of the galaxies and the observed velocities of the stars within them, could be some other strange thing, so there is nothing to stop scientifically informed speculation as to some other cause.

The dark matter problem was already well known to Fritz Zwicky in the 1930s, as he had measured the velocities of the galaxies within large clusters of galaxies, and he had found that the orbital speeds of the galaxies were so high..... that several times the observed amount of visible (luminous) matter was required to keep the cluster of galaxies stable (to stop the galaxy cluster from flying apart)

Tiny dwarf galaxies have the same problem, in that much much much more matter is required to hold them together than is observed. In particular, the faintest dwarf galaxies have very-widely spaced stars, and very few stars in them. The observed amount of luminous matter in these tiny dwarf galaxies is ridiculously small, yet they do hold together;
at the extremes, two or three hundred times the observed amount of matter is required to hold together an ultra-low-luminosity dwarf galaxy!

Obviously, the existence of a galaxy which looks like a powder-puff, but which seems to be dominated by large densities and amounts of dark matter , does cause some astronomers to wonder if that vast amount of additional "dark" matter is really there?

So I think it is natural to wonder, given that dwarf galaxies exist where the gravitational field requires one or two hundred times the observed amount of matter, whether all of that additional matter is really there. But this sort of thinking comes under the heading of "interesting speculations"
___________________________________ _____________


And you guys (not sjastro...) , stop lumping dark energy and dark matter together.
(so I suggest that you get educated(!!) as to exactly how stars and galaxies do move, and you will see the difference. The observed line-of-sight velocities of stars and galaxies, and increasingly, their transverse velocities "across the observed sky", constitute a vast existing set of observations and data , all of which can be explained perfectly-well by the dark matter hypothesis and standard gravity. However, astronomers still do look for other explanations for the velocities of galaxies, such as "large scale cosmic flows")

Dark matter is very-well-established and nearly universally assumed to exist by all professional astronomers!!
(science, unlike theology, does not deal in certainty, so when astronomers become perhaps 70 percent certain that black holes exist and 70 percent certain that dark matter exists, they allow themselves to talk of these things as if they really do exist)


In contrast to the status of Dark Matter, Dark Energy is at the frontier of what can currently be observed and understood.

__________________________

There are currently a number of surveys, in progress and in planning, of very large numbers of galaxy redshifts (line-of-sight velocities of galaxies) that are designed to look for exotic effects such as dark energy and "boojums"(= unknown effects), but this should not detract from the fact that the velocities of things in space are pretty much universally explainable by standard gravitational theory.
___________________________

[xelasnave]

Hi Robert
Firstly thank you for your post I found it very interesting.
I was under the impression that dark matter was a form of matter which in effect we are unaware of its nature, further that it is something exotic and not normal matter.
Your post hints that it may be dust or stars even journals that dont throw light on anything are we to take this to mean that some exotic particle is but one option and somewhat normal matter may be there but we simply can not detect it.
I have the impression that dust stars or journals would be detectable by means other than gravitational influence. Are we to take it that this dark matter may indeed be normal matter, for example dust issolated planets er rocks without a sun and that the prospect of a new particle is but one of the prospects for dark matter.

Your comments re dwarf galaxies surprised me as to the amount of dark matter required.
Two to three hundred times more dark matter required I find extraordinary.
I have heard numbers which suggest a great deal more dark matter than ordinary matter but two to three hundred times more in a specific situation makes me think back to my original concern that our sums are wrong.
It seems inconceivable (of course anything outside human experience can be inconceivable) that in the case of our dwarf galaxy finding we observe one two hundreth or one three hundreth of the matter really should suggest we seek a review of our current science on gravity.
You are lucky in that you have not heard me rattle on about gravity in effect working like a pressure system, that is force acting from the outside in not in a fashion we term attraction, but if gra ity acted as a form akin to external pressure I doubt if we would need such enormous amounts of dark matter if indeed we need any.
Unfortunately I cant take it further with any theory or even drag together enough to lable my tboughts as a hypothisis.
I just think unless you can say our dark matter may be dust rock or some normal matter to search for new matter just seems somehow more an effort to resist altering our math and our theory of gravity.
The huge amount of dark matter required in the case of a dwarf galaxy scfeams to me that we need to investigate alternative gravity theories... Even the somewhat discredited theories that hint of no dark matter.

I suffer from no education in this matter and look to you (and always Steven) for help.
I am not a nutter orcrank in that I really do try to understand and accept mainstream position.
Alex

[madbadgalaxyman (Robert)]

Originally Posted by xelasnave

Hi Robert
Firstly thank you for your post I found it very interesting.
I was under the impression that dark matter was a form of matter which in effect we are unaware of its nature, further that it is something exotic and not normal matter.

Hi Alex,

Well, all we have to go on is the observations of the velocities of galaxies and stars and other astronomical objects. In fact, mainly, with the spectrograph attached to our telescope, we can find only the 'radial' (in the observer's line-of-sight) velocities of astronomical objects.
Subject to various assumptions, we can convert these radial velocities of objects into approximate (statistically correct)(averaged) knowledge about the orbits and velocities of astronomical objects in three-dimensional space.

The most parsimonious assumption, without introducing unnecessary and additional hypotheses (= Occam's razor), is simply that the observed velocities of galaxies and stars , because they do not correspond to the velocities that we would expect to observe if these objects were just under the influence of the matter we can observe by means of its emission of electromagnetic radiation (light, X-rays, infrared, radio waves, etc.), are best explained by the combined influence of gravity that comes from ::
(1) a component of matter which we can easily see from its emission of photons
(2) Another component of matter which is currently not detectable at any wavelength, with the current state-of-the-art Light Gathering Power and sensitivity and noise-level of our telescopes and detectors.

Originally Posted by xelasnave

Your post hints that it may be dust or stars even journals that dont throw light on anything are we to take this to mean that some exotic particle is but one option and somewhat normal matter may be there but we simply can not detect it.

All we know is that there is a lot of additional gravity there that we cannot account for.........the galaxies and the clusters of galaxies would not be stable, and would fly apart, if all that was holding them together was the gravity from the observable stars and gas and other objects.
But of course, the objects that are producing the necessary additional gravity are not known, as we cannot currently detect them with our telescopes and their attached instruments. As mentioned, Zwicky knew about this in the 1930s, from his observations of the orbits of galaxies within clusters of galaxies, but astronomers were not ready to accept this implication until the early 1970s.

Originally Posted by xelasnave

Your comments re dwarf galaxies surprised me as to the amount of dark matter required.
Two to three hundred times more dark matter required I find extraordinary.
but two to three hundred times more in a specific situation makes me think back to my original concern that our sums are wrong.

Alex, the sums are not wrong, if we assume conventional gravitational theory, and while it seems far-fetched to believe that 299/300 of the mass of a dwarf galaxy is in some unknown form, very simple algebraic calculations of the sort that some of us learn to do in Year 12 Physics Class show that the gravitational effect of this additional matter is there and likely to be real. Which gets back to my original point that there is no reason to believe any other hypothesis about the origin of the velocities of galaxies and their constituent stars.

The case of dark matter may be compared to the case of the theory of evolution........
the story revealed by science seems extraordinary, and perhaps counter-intuitive, but "these are the truths that we must cling to, in the absence of further observations disproving them or modifying them".

As I mentioned before, science cannot provide absolute certainty, and we can only say that it is more likely than not that something is true. So, for now, we must earnestly speak about dark matter as being something real, as that is where the current observations point.

Originally Posted by xelasnave

I suffer from no education in this matter and look to you (and always Steven) for help.
I am not a nutter orcrank in that I really do try to understand and accept mainstream position.

I absolutely respect your open mind, and your strong desire to learn ever more about what is physically real and what is not physically real, in this grand universe of ours.

[xelasnave]

Thank you Robert for taking so much of your time to help me I sincerely appreciate your effort.
Alex

[croweater (Richard)]

Hi crew, Are the galaxies surrounded by dark matter or actually in clouds of dark matter? Would gravity waves be emitted? Thanks Richard

[julianh72 (Julian)]

Alex,

I'm probably going to sound like I'm advertising for Penguin Books because of the number of my recent posts advocating "Universal: A Guide to the Cosmos" by Brian Cox and Jeff Forshaw https://www.penguin.co.uk/books/180728/universal/ but I'm not, I've just found it to be a superb account of the state of modern cosmology.

It's current (published September 2016), and very readable, being co-authored by two excellent public-outreach scientists. (Brian Cox will be very well known to most of us; Jeff Forshaw less so, but he has worked with Brian Cox before.)

What I really like about the book is that explains and presents the actual data which is being relied upon, outlines the maths which is used to interpret it, and invites the reader to work it out for themselves using the data, graphs and formulae provided. It also explains how data collected from multiple, completely different sources supports the same conclusion - Dark Matter, Dark Energy, and accelerating expansion of the Universe are not simply an artefact of a single set of observations, or an empirical requirement to force a particular theory to match a subset of the data.

Like you, I find it hard to comprehend that we simply can't detect most of the "stuff" that makes up the Universe, and don't even have a solid consistent theoretical basis to understand what that "stuff" is, and yet, that is where the observations take us.

The good news is that this means that "Science isn't dead" - we know that we still have much to learn. I think it must be something similar to the state of Classical Physics at the end of the 19th Century and early 20th Century - there was a feeling that we pretty much understood everything, and all we had to do was dot the Is and cross the Ts - and then along came Einstein, quantum mechanics, etc, and suddenly, we realised that we understood nothing!

[madbadgalaxyman (Robert)]

Originally Posted by croweater

Hi crew, Are the galaxies surrounded by dark matter or actually in clouds of dark matter? Thanks Richard

There are a lot of small galaxies about which are constantly merging with big galaxies like the Milky Way and M31 and NGC 253, and these tiny dwarf spheroidal galaxies are thought to be dark-matter dominated (as per my recent two posts), so this would argue for a certain amount of lumpiness in the dark matter halo of a big galaxy.

The scientific work on the amount and distribution of dark matter in the halos of galaxies involves using small objects that rotate around a galaxy ( like globular clusters and planetary nebulae) and measuring the component of the velocity of each object that we can observe;
measuring the radial velocity of each object. These orbiting objects are used as "test particles" to try to figure out the distribution and amount of gravitating matter (= "bright"(luminous) matter plus "dark matter") around a galaxy.

Another way is to observe the X-ray emitting gaseous halo of a galaxy or cluster of galaxies and to try to figure out how much mass is needed to stop the gas from escaping the galaxy or galaxy cluster.

You can also use gravitational lensing of the light from a background object behind a massive object like a cluster of galaxies ,in order to try to figure out the amount of gravity and matter that is in the path of the light rays from a more distant object. The gravitational bending of light from background objects is one of the most important pieces of evidence for the existence of large amounts of matter in some form that is currently not detectable in photon emission.

I will have to pass on the question of the structure of dark galaxy halos, as I am not up on the current literature!