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New class of galaxy has been discovered, made almost entirely of dark matter

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Re: New class of galaxy has been discovered, made almost entirely of dark matter

#81
post #34

I find myself wondering if the type of inference required to make this claim could be automated. Given the right observations, couldn't dark matter be detected (or at least hypothesized) algorithmically? Couldn't this be used to create a "dark matter scope" by which the dark matter in the universe can be "seen" and visualized?

Not everything can be automated, but there is certainly at least some machine learning in all of the larger surveys these days. As to dark matter surveys explicitly, I found this one: http://kids.strw.leidenuniv.nl/pr_july2015.php

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#82
post #53

Earlier quoted context omitted.

No infrared. Already ruled out by earlier infrared surveys looking for Dyson spheres.

We often seem to assume we know "everything", and we often find out there is more to learn. It would be an interesting universe if we found dark matter to be ancient civilisations. Using up much of the mass and energy (even the infrared).

Oh stop. This is such an unlikely avenue of inquiry that it just distracts from the conversation.

If at some point we figure out that the laws of thermodynamics do not apply, that would be such a profound change in how we interact with the universe that speculation over how to best search the night sky for intelligent life would be the last thing on most people's minds for quite some time.

We would quickly find ways to harness quantities of energy that would fry us to a literal crisp today due to conversion losses, and that would be such a breakthrough that rather than look for signs of life in nearby systems, we could just go there and look around.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#83
post #53

Is it possible that an alien race has simply covered that galaxy with dyson spheres? That life is more common than we thought - or perhaps more rapidly advancing once intelligence is hit - and most galaxies are "dark" from their interference?

No infrared. Already ruled out by earlier infrared surveys looking for Dyson spheres.

Ruled out? From Wikipedia:

Identifying one of the many infrared sources as a Dyson sphere would require improved techniques for discriminating between a Dyson sphere and natural sources. Fermilab discovered 17 potential "ambiguous" candidates, of which four have been named "amusing but still questionable". Other searches also resulted in several candidates, which are, however, unconfirmed.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#84
post #79

Earlier quoted context omitted.

No, it would speed past the center until losing moment on the surface of the other side of the planet, and oscillate back and forth. Because there's no "friction" slowing down the dark matter it will continue like this forever, by conservation of energy. Check out http://physics.stackexchange.com/questions/214950/if-dark-ma...

> speed past the center What caused these particles to accelerate up to the speeds they are at in the first place, then? Something must be interacting with them quite significantly if they have non-zero velocity?

the force of gravity

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#85
came across this paper that investigates how the EM propulsion drives might generate thrust, and as a side effect, the theory explains certain phenomena that we attribute to dark matter and dark energy. i only have undergrad physics degree, but it sounds interesting. anyone with more experience have any thoughts about this?

http://arxiv.org/pdf/1604.03449v1.pdf >McCulloch (2007) has proposed a new model for inertia (MiHsC) that assumes that the inertia of an object is due to the Unruh radiation it sees when it accelerates, radiation which is also subject to a Hubble-scale Casimir effect. In this model only Unruh wavelengths that fit exactly into twice the Hubble diameter are allowed, so that a greater proportion of the waves are disallowed for low accelerations (which see longer Unruh waves) leading to a gradual new loss of inertia as accelerations become tiny. MiHsC modifies the standard inertial mass (m) to a modified one (m_i) as follows:

m_i = m (1-(2c^2)/(|a|Θ)) = m (1 - λ/4Θ) (1) where c is the speed of light, Θ is twice the Hubble distance, ’|a|’ is the mag- nitude of the relative acceleration of the object relative to surrounding matter and λ is the peak wavelength of the Unruh radiation it sees. Eq. 1 predicts that for terrestrial accelerations (eg: 9.8m/s2) the second term in the bracket is tiny and standard inertia is recovered, but in low acceleration environments, for example at the edges of galaxies (when a is small and λ is large) the sec- ond term in the bracket becomes larger and the inertial mass decreases in a new way so that MiHsC can explain galaxy rotation without the need for dark matter (McCulloch, 2012) and cosmic acceleration without the need for dark energy (McCulloch, 2007, 2010).

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#86
post #79

Earlier quoted context omitted.

No, it would speed past the center until losing moment on the surface of the other side of the planet, and oscillate back and forth. Because there's no "friction" slowing down the dark matter it will continue like this forever, by conservation of energy. Check out http://physics.stackexchange.com/questions/214950/if-dark-ma...

> speed past the center What caused these particles to accelerate up to the speeds they are at in the first place, then? Something must be interacting with them quite significantly if they have non-zero velocity?

Gravity.

Actually, almost the only thing that we know about dark mater is that gravity affect it.

(Actually, we only know that there is something that is making a gravitational pull of normal mater, and we call this mysterious thing "dark mater".)

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#87
post #53

Earlier quoted context omitted.

No infrared. Already ruled out by earlier infrared surveys looking for Dyson spheres.

Ruled out? From Wikipedia: Identifying one of the many infrared sources as a Dyson sphere would require improved techniques for discriminating between a Dyson sphere and natural sources. Fermilab discovered 17 potential "ambiguous" candidates, of which four have been named "amusing but still questionable". Other searches also resulted in several candidates, which are, however, unconfirmed.

I think aab0 means that this particular galaxy is ruled out as a Dyson sphere, not the possibility of there being one somewhere in the universe.

A Dyson sphere should still emit infrared, unless the aliens can subvert thermodynamics, at which point anything is possible.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#88

Earlier quoted context omitted.

I've always wondered, if gravity is a wave (has it been confirmed?), then there must be areas in space where different waves superimpose. Would the constructive interference between gravity waves be significant enough to account for 'dark matter'? And what would destructive interference look like (dark energy?)

Gravity waves are caused by moving objects, and the waves themselves move. So if you did see constructive interference between gravity waves, it would be temporary. Gravity waves also tend to be extremely small, small enough that it was only this year (2016) that we were finally able to detect them (at LIGO). Here's a video of what standing waves look like in water: https://www.youtube.com/watch?v=NpEevfOU4Z8

Ah, so 'Gravitational waves' are ripples in spacetime.

But, if gravity itself propagated as a wave (graviton + duality?) could interference explain dark matter/energy?

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#89
post #34

I find myself wondering if the type of inference required to make this claim could be automated. Given the right observations, couldn't dark matter be detected (or at least hypothesized) algorithmically? Couldn't this be used to create a "dark matter scope" by which the dark matter in the universe can be "seen" and visualized?

I'm guessing here, but they probably detected this automatically. There are millions of millions of galaxies and you can't put a even graduate student to look at each one.

My guess is that they were preparing a boring paper, like "Analysis of Normal/Dark Matter ratio in WhAtEvEr type galaxies near SoMeWhErE". They put a telescope, some processing and then they transfer the data to Excel to make a nice graphic. Then got some outliers, and with more analysis they were discarded as error. But they got one nasty outlier that were not easy to kill. They measure it again, and again, and probably made another team double check it.

(Perhaps they were looking for faint galaxies, and it was not too much luck.)

Anyway, probably most of the calculation was automated, and probably now some other teams will try to find similar objects.

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