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The Reason We Haven’t Directly Detected Dark Matter

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Re: The Reason We Haven’t Directly Detected Dark Matter

#41
This may be a dumb question, but could dark matter just be regular matter, like planetoids? What if interstellar space had a light sprinkling of things like Oumuamua?

On an interstellar scale, maybe this could create the lensing effects and explain some other phenomena. Is it unreasonable that 5/6 of the mass of the universe is like the stuff that makes up planets, but isn't lit up as brightly as a star?

Re: The Reason We Haven’t Directly Detected Dark Matter

#42

Earlier quoted context omitted.

As I understand it, gravity is the interaction between things with mass, but it's a weak interaction, thus hard to detect on a particle by particle basis. You might be able to detect if there's an extra potato in a bag because a potato is a whole bunch of particles. But identifying that just a few of those particles are not the regular stuff -- protons, electrons, etc. -- by weighing the bag, would be difficult.

But you do not need to measure it particle by particle. Just because those have mass, there should be a bunch of dark matter particles hanging around with earth. And given that we have quite good idea what earth consists of, there should be a discrepancy in some of the measurements that use earth's mass against the mass we have from our understanding of earth's composition. Unless, of course, the extra mass of earth…

Indeed the mass of dark matter is why we think there is dark matter -- discrepancies such as you mention, but evident from astronomical observations. The problem for characterizing the particles is: Mass and what else? The what else is the thing people are trying to detect.

Re: The Reason We Haven’t Directly Detected Dark Matter

#43

If we can't detect it or disprove it, it doesn't even belong to science. It belongs to the same realm as witches and demons - until some smart physicist devises a way to actually detect it.

You have to have a theory to test before you can test it. If they are stating as fact something that hasn't been proven, that's a problem. If they are testing the assumptions which closest matches the data, that is science.

Re: The Reason We Haven’t Directly Detected Dark Matter

#44

We have a room filled with one foot of iron, one foot of sand, one foot of water, one foot of air, and some empty space filled with god knows what needs to be filled in order to balance the gravity equations. There is one group of people looking for particles less dense than air to fill the rest of the room. I am in the group that's looking at the other end for particles denser than iron, and I firmly believe they ar…

You can "firmly believe" in whatever you want. That's not science, that's belief. The evidence points towards the existence of dark matter very strongly, and the evidence has eliminated the possibility of dark matter being made up primarily of black holes. Which, incidentally, do exist and are not "black stars" (the gravitational wave detections of merging black holes are the strongest evidence yet of the existence of black holes and don't leave wiggle room for alternate theories).

If you don't form your beliefs based on where the evidence leads you then you are not following science, period.

Re: The Reason We Haven’t Directly Detected Dark Matter

#45
post #23

Earlier quoted context omitted.

> It has mass, so it by definition interacts with anything with mass? Yeah, but the only interaction is gravity. And nothing that clumps these particles together (such as the electro-magnetic force for ordinary matter). > Are these particles supposed to be so small and so rare that they can't be measured even at the scale of solar system? The additional mass can be measured, this is why we suspect the particles are t…

> The additional mass can be measured, this is why we suspect the particles are there in the first place :) Yes, in interstellar scale. How much there should be dark matter within solar system? 1 gram? 1 kilogram? I mean, if there was supposed to be 5/6 parts of mass of dark matter within solar system, it would quote obviously be somehow observable?

The thing you are missing is that the "missing mass" isn't observable on the scale of the solar system. It's missing on the scale of large scale galactic structures -- i.e. lots and lots of galaxies. When we look at those structures, we can't figure out how they got that way unless there is a whole bunch more mass than there looks to be. Apart from that, we know nothing.

People speculate that maybe there is some weird particle that we can't see in any other way than through looking at the mass of these large (really, really, really ridiculously large) structures. But is there any of it in the solar system? In our galaxy? Nobody knows. Does it hang out between galaxies? Between galaxy clusters? Does it even really exist? Nobody knows.

You're just jumping way, way, way too far down the way ;-) Literally, dark matter could be anything -- even a misunderstanding about how the universe works. That's what's interesting about it.

Re: The Reason We Haven’t Directly Detected Dark Matter

#46
post #38

So, basically physicists have deduced two facts, and these facts don't agree with one another. From this they conclude that there must be something else in the universe, something unseen and undetectable, that they call dark matter. But what about the other possibility, which seems far more reasonable to me, that either one of the facts is wrong?

It is not "one fact", it's a whole string of evidence (as partly explained by the article). The evidence strongly supports the dark matter theory and the evidence has consistently eliminated every single other theory attempting to explain the phenomena.

Re: The Reason We Haven’t Directly Detected Dark Matter

#47

This may be a dumb question, but could dark matter just be regular matter, like planetoids? What if interstellar space had a light sprinkling of things like Oumuamua? On an interstellar scale, maybe this could create the lensing effects and explain some other phenomena. Is it unreasonable that 5/6 of the mass of the universe is like the stuff that makes up planets, but isn't lit up as brightly as a star?

Not a dumb question, but obviously they've thought of that:

https://en.wikipedia.org/wiki/Dark_matter#Baryonic_matter

Re: The Reason We Haven’t Directly Detected Dark Matter

#48

If we can't detect it or disprove it, it doesn't even belong to science. It belongs to the same realm as witches and demons - until some smart physicist devises a way to actually detect it.

We can detect it, gravitationally. The Bullet cluster is pretty incontrovertible evidence that dark matter exists.

It's detecting it through other interactions that's proving extremely difficult.

Re: The Reason We Haven’t Directly Detected Dark Matter

#50

This may be a dumb question, but could dark matter just be regular matter, like planetoids? What if interstellar space had a light sprinkling of things like Oumuamua? On an interstellar scale, maybe this could create the lensing effects and explain some other phenomena. Is it unreasonable that 5/6 of the mass of the universe is like the stuff that makes up planets, but isn't lit up as brightly as a star?

This is the "MACHO" (massive compact halo objects) theory, which has been tested and disproven. The missing mass can't be gas or dust clouds because that would have certainly observational traces which we have looked for and don't exist. It can't be planetoids because that would cause a frequency of gravitational micro-lensing of stars in other galaxies that we do not observe.
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