Another reason may be that dark matter doesn't exist. If the universe consists of 85% of the stuff it would seem that it should be easy to find. Occams razor should apply as usual.
The Reason We Haven’t Directly Detected Dark Matter
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Re: The Reason We Haven’t Directly Detected Dark Matter
#22I'm guessing that "guessing in the dark" is the way experiments for particles in the standard model have been done for a while now. I would assume that a single success would set off a chain reaction as the author said.
I'd say it's not completely in the dark. The experiments try to test theories that suggest where to look. For instance if a theory predicts a previously un-discovered particle, with some rules for how it interacts, then you can refine your search based on those rules -- what range of masses you're looking for, what decay patterns, and so forth.
Re: The Reason We Haven’t Directly Detected Dark Matter
#23My attempt to summarize the reasons would be: We haven't directly detected dark matter because we don't really know what we are looking for, and there are only a few things we can search for. Dark matter might not be structured in a way we can investigate with current technology. Also, dark matter doesn't interact much with regular matter, which makes the search even harder.
> Also, dark matter doesn't interact much with regular matter, which makes the search even harder. This is (one of the many places) where I get lost. It has mass, so it by definition interacts with anything with mass? Are these particles supposed to be so small and so rare that they can't be measured even at the scale of solar system? (How much dark matter would be in the solar system? What would be the average densi…
> 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 there in the first place :)
Re: The Reason We Haven’t Directly Detected Dark Matter
#24My attempt to summarize the reasons would be: We haven't directly detected dark matter because we don't really know what we are looking for, and there are only a few things we can search for. Dark matter might not be structured in a way we can investigate with current technology. Also, dark matter doesn't interact much with regular matter, which makes the search even harder.
> Also, dark matter doesn't interact much with regular matter, which makes the search even harder. This is (one of the many places) where I get lost. It has mass, so it by definition interacts with anything with mass? Are these particles supposed to be so small and so rare that they can't be measured even at the scale of solar system? (How much dark matter would be in the solar system? What would be the average densi…
Dark matter’s interaction with “regular” matter via gravity is covered in the article. It also interacts with light via gravity.
Measuring the interactions between galaxies, and things like gravitational lensing are providing evidence of dark matter’s existence.
Re: The Reason We Haven’t Directly Detected Dark Matter
#25Earlier quoted context omitted.
We know how stars work, and we know how gravity works...These two numbers don’t match, and they don’t match spectacularly. There had to be something more than just stars responsible for the vast majority of mass in the Universe. I think the problem here is that maybe there is something else we don't understand. We also did not understand the propagation of light in a vacuum in the 19th century, and invented a hidden…
Perhaps we could call that thing: "dark matter" for now. In seriousness, we can observe the effect, and even map the distribution of the stuff.
That assumes that it is "matter". Maybe there is something we just fundamentally don't understand about gravity.
Re: The Reason We Haven’t Directly Detected Dark Matter
#26Another reason may be that dark matter doesn't exist. If the universe consists of 85% of the stuff it would seem that it should be easy to find. Occams razor should apply as usual.
That's not Occam's razor. The razor applies to theories with identical predictions and tells you to pick the simplest one. I'm not sure how you got your inference from Occam's razor.
Re: The Reason We Haven’t Directly Detected Dark Matter
#27Earlier quoted context omitted.
> Also, dark matter doesn't interact much with regular matter, which makes the search even harder. This is (one of the many places) where I get lost. It has mass, so it by definition interacts with anything with mass? Are these particles supposed to be so small and so rare that they can't be measured even at the scale of solar system? (How much dark matter would be in the solar system? What would be the average densi…
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 due to dark matter is calculated in e.g. kilograms. That's why I would like to know the expected density of the dark matter.
Re: The Reason We Haven’t Directly Detected Dark Matter
#28Because it doesn’t exist. Dark matter is a fudge factor to prop-up a theory that astrophysics is too afraid to put to rest.
We know how stars work, and we know how gravity works...These two numbers don’t match, and they don’t match spectacularly. There had to be something more than just stars responsible for the vast majority of mass in the Universe. I think the problem here is that maybe there is something else we don't understand. We also did not understand the propagation of light in a vacuum in the 19th century, and invented a hidden…
Who knows what future physics holds (I’d love to know!) but our best theory of gravity (Einstein’s general relativity) is shown to be amazingly accurate in every experiment ever conducted for it.
Some form of only-detectable-via-gravity matter fits the math. Coming up with provable alternative math would be the greatest scientific breakthrough of the past century...or possibly of all time.
I’m sure people are working on it (along with quantum gravity). So either it’s wrong or it’s dark matter.
Re: The Reason We Haven’t Directly Detected Dark Matter
#29Earlier quoted context omitted.
> Also, dark matter doesn't interact much with regular matter, which makes the search even harder. This is (one of the many places) where I get lost. It has mass, so it by definition interacts with anything with mass? Are these particles supposed to be so small and so rare that they can't be measured even at the scale of solar system? (How much dark matter would be in the solar system? What would be the average densi…
> 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?
Re: The Reason We Haven’t Directly Detected Dark Matter
#30Another reason may be that dark matter doesn't exist. If the universe consists of 85% of the stuff it would seem that it should be easy to find. Occams razor should apply as usual.
> If the universe consists of 85% of the stuff it would seem that it should be easy to find.
How did you infer this? We are bathed in gravitational waves but they weren’t “easy” to find.
> Occams razor should apply as usual.
So what would be your razored explanation for the gravitational anomalies that point to the presence of matter we cannot see?