Is Dark matter Necessary?

[pantheory]

Is Dark Matter necessary?

 

Hypothetical entities like dark matter and dark energy have been proposed to explain observations that otherwise seem difficult to explain. Three of the main reasons dark matter was proposed in the first place was 1) to explain the stellar orbital velocities of stars in the disks of spiral galaxies 2) to explain orbital rates of galaxies in a cluster 3) to explain the extent of galactic lensing whereby it would take a lot more matter than what we can see to bend light as mush as we observe. There were also other theoretical advantages to this proposal.

 

There have been few alternative proposals to dark matter. One approach was to change the formulation of gravity concerning the effect of gravity per distance in a spiral galaxy, concerning 1 and 2 above. This was the approach of MOND gravity (Modified Newtonian Dynamics). This proposal, although somewhat successful in explaining problem #1, was less successful in explaining #2, and says nothing about #3.

 

Another big problem with the MOND formulation is that it does not address why the force of gravity should change under different circumstances.

 

A different approach from MOND might be to explain how by using the Newtonian formulation one can explain what is being observed. Newton’s gravity formulation can derive Kepler’s gravity mechanics, and rate of orbital motions. The equation for orbital velocities in a circular orbit would be:

 

v = (GM/r)^.5

 

https://en.wikipedia.org/wiki/Orbital_mechanics

 

If the application of this formula were different, the results would be different. Instead of the mass of the galaxy being considered constant, and the only variable would be a star's distance from the center of the galaxy, both the mass and distance could be variables based upon Newton's shell theorem, where only the mass of the galaxy on the inside of a star's orbit would be considered.

 

https://en.wikipedia.org/wiki/Shell_theorem

 

So as the radius away from the center of the galaxy would increase, so would the mass that would affect the stellar orbital velocity. This could produce a constant orbital speed of stars within the galaxy, or faster stellar speeds toward the outside diameter of the galaxy, if stellar densities outward were close to being equal to inner densities. To test such a hypothesis galactic stellar orbital motion data from a number of different galaxies would be needed and then tested. This could also seemingly explain motions of galaxies in a cluster when they tend to orbit each other on somewhat the same orbital plain. As to #3, either the mechanics of galaxy lensing would need to be explained differently concerning its application, such as an additional refraction characteristic, or explanations would be needed to explain why an adjustment to the bending of light formulation would be needed at galactic scales.

 

Dark Matter is not that easily explained away.

Edited September 4, 2014 by pantheory

[Strange]

I.e. in accordance to "basic thermodinamics" temperature of DS would be about 60 degrees, or undetectable. (Even if we do not count the m=E/c^2 option).

 

That is significantly warmer than the background. And as you are assuming that there are 5 times as many of these spheres as there are visible stares, that would be readily detectable.

 

The discussion you link to is about hiding a single Dyson sphere by pumping all the excess heat to, say, another nearby planet. So you still end with 6 times as many heat sources as there are stars - just not co-located with the Dyson sphere. So now you have twice as much chance of detecting them: gravitational lensing and occlusion by the Dyson sphere (easily detectable but not found yet) plus these extra heat sources at some distance from it.

 

Once again, you are proposing a civilization with "sufficiently advanced technology" to be spread throughout the universe on a massive scale (5 times as many spheres as stars, remember) but keeping themselves completely invisible.

 

And you think this is simpler than the rather mundane idea of yet another type of particle that does not interact with other matter?

 

I wonder what fantastic explanations you would have come up with before Neptune and neutrinos were discovered. Invisible alien spaceships pushing Uranus around? Teeny-weeny aliens taking energy away from atomic nuclei?

 

And you are ignoring the half dozen or more fundamental reasons why it cannot work. It's not like no one has ever thought of it before. The difference is, they did the math and found it doesn't work.

 

Can you show us the math you have done to convince yourself this idea works?

[SciChallenger]

Hi Strange,

Thank you for your comment. Sorry I did not reply yesterday, I was too busy. Basically you are repeating the same mistakes as before, and namely posting the criticism without reading the source.

 

>1. The discussion you link to is about hiding a single Dyson sphere by pumping all the excess heat to, say, another nearby planet.

 

I provided link to this discussion because it contains calculations of Dyson sphere surface temperature made by Rod Vance (what I specified in my post). These calculations show that for DS with the size of Pluto orbit the temperature would be 0.01 of Sun surface or about 60 degrees.

 

>2. And as you are assuming that there are 5 times as many of these spheres as there are visible stares, that would be readily detectable.

 

Can you provide any link (or reference to offline article) that supports your statement that object with temperature about 60 K on the distance of several light years would be "readily detectable" by their radiation? (Yes, we detect exoplanets, but by their gravity, not by radiation.) If you cannot prove this, your comment becomes incorrect and misleading.

 

>3. So now you have twice as much chance of detecting them: gravitational lensing...

The gravitational lensing detection of DS was analyzes in details in the article published on IntellectualArchive.com .

Basically, gravitational lensing researches expected the lambda-shaped graphs (like letter "A"), since the size of objects (brown dwarfs, black holes, planets etc.) are small and their "shadows" rarely influence the brightness of stars passing behind them. The DS have much bigger size and therefore were excluded from the objects detected by A-shaped graph of star brightness, which microlens researchers looked for. For DS we can expect the M-shaped or even U-shaped graph of star brightness when it travels behind the DS.

These graphs were not analyzed by gravitational lensing researches. However with their material they can make this analysis and confirm the DS existence or absence.

 

>4. And you think this is simpler than the rather mundane idea of yet another type of particle that does not interact with other matter?

Absolutely. If there is nothing that contradicts the DS explanation of hidden masses - we definitely do not need to introduce new type of matter, which is not detectable and which has the only purpose - to reconciliate the math.

 

Question is – does astronomy have material of observations that rejects the DS explanation? The mentioned article on www.IntellectualArchive.com is merely question, not statement.

 

>5.Teeny-weeny aliens taking energy away from atomic nuclei?

No comments, sorry.

[Strange]

 

Question is – does astronomy have material of observations that rejects the DS explanation?

 

Yes. But you will ignore it all.

[SciChallenger]

Regarding
I wonder what fantastic explanations you would have come up with before Neptune and neutrinos were discovered

 

Since we are discussing the dark matter here,

In your analogy with the Uranus orbit anomalies, should astronomers introduce the invisible "dark matter" that does not interact with our world and has the only purpose to explain the anomalies of Uranus orbit? Or they should use the Occam razor and look for our world object (Neptune), which was not known at that time?

Edited September 5, 2014 by SciChallenger

[Strange]

Or they should use the Occam razor and look for our world object (Neptune), which was not known at that time?

That is exactly what has happened with dark matter. Initially, it was just a "place holder" name for whatever-it-is that causes the observed effects (See also: dark energy); that could have been a change to the way we understand gravity, extra normal matter we just can't see for some reason, black holes, some new physics, huge numbers of Dyson speheres, a formerly unknown particle or particles, etc.

 

All of those are things we have come across before. (with the exception of one - guess which - and therefore, guess which is ruled out by Occam's razor.)

 

Now, the multiple strands of evidence overwhelmingly point to non-baryonic matter. Obviously, people are still looking at alternatives (MOND-type theories keep coming close but just not close enough). But they do that by doing a detailed analysis of the likely effects and comparing those with observation. Your cherry-picking of bits of information that appear to bolster your idea, and ignoring those that don't, does not meet the necessary standards to be compelling.

 

By the way, I assume you wrote the article you keep referring to?

Edited September 5, 2014 by Strange