Re:A Physicist Who Denies That Dark Matter Exists
by Paul-ish on Monday February 27, 2017 @01:52PM
(#13746713)
> And sure, dark matter is falsifiable. If observations are made where gravity appears to deviate from what's visible and can't be explained by adding invisible mass, that would falsify it.
Whats to stop us from "adding epicycles" when that happens?
Re:A Physicist Who Denies That Dark Matter Exists
by mikeash on Monday February 27, 2017 @07:52PM
(#13750151)
The same thing that stopped the addition of epicycles to the geocentric model of the solar system: a better theory that explains the observations more naturally.
Re:A Physicist Who Denies That Dark Matter Exists
by EGreg on Monday February 27, 2017 @12:03PM
(#13745678)
How do we know dark matter isn't just really transparent matter? Like, we can't see it in space but it's there, not reflecting or deflecting enough light for us to detect it.
Re:A Physicist Who Denies That Dark Matter Exists
by XorNot on Monday February 27, 2017 @12:27PM
(#13745927)
Because it would collide with itself. Dark matter isn't just "not visible" - it's non-electromagnetic. As observed it didn't aggregate when colliding with itself, so there aren't big dark matter made black holes around, nor gravity anomalies from dark matter nebula or the like.
Two dark matter particles headed directly at each other would pass through each other and be only slightly deflected by their gravitational interaction.
Re:A Physicist Who Denies That Dark Matter Exists
by btilly on Monday February 27, 2017 @07:36PM
(#13750067)
Not necessarily. Dark matter could be made of small dense objects. Because they are small, we wouldn't see absorption of light. And because they are small, they will very seldom collide. These kinds of object are called MACHOs.
Based on observed dimming events while monitoring many stars, we have ruled out brown dwarfs as more than 20% of the total. Other possibilities still remain, but none have shown evidence of being sufficient to explain dark matter. However we have not ruled out the possibility of it being something that we haven't thought of yet.
Re:A Physicist Who Denies That Dark Matter Exists
by scatters on Monday February 27, 2017 @12:28PM
(#13745934)
Yes, that's what cosmologists mean by "dark": not interacting with light of any observable wavelength, to any detectable degree.
Re:A Physicist Who Denies That Dark Matter Exists
by Y_Y on Monday February 27, 2017 @01:37PM
(#13746595)
It could be[0]. It's just not very likely, since you'd have to have very special circumstances, but it's not logically impossible, at least in cosmology.
Re:A Physicist Who Denies That Dark Matter Exists
by yati on Monday February 27, 2017 @12:37PM
(#13746027)
From what I understand, if dark matter is stuff that only interacts gravitationally, by definition it is transparent to light. Also collisions, being ultimately electromagnetic interactions, aren't observed. So it's not transparent in the sense of glass. But I'm not a physicist, and this thread is interesting :)
Re:A Physicist Who Denies That Dark Matter Exists
by TheHegemon on Monday February 27, 2017 @12:27PM
(#13745925)
Like some kind of dark matter?
Neutrinos were actually an early candidate for dark matter. The numbers didn't work out, but it's an example of something that would interact weakly.
And sure, dark matter is falsifiable. If observations are made where gravity appears to deviate from what's visible and can't be explained by adding invisible mass, that would falsify it. Or if someone finally comes up with a change to the known laws of physics which explains the observations better than dark matter does, that would do it.
Remember, nothing is truly "directly observed." All we can do to observe stuff is to see how it affects other stuff. Whether it's with photons or with gravity, it's all ultimately indirect.