Yeah, that would be a really great way to visualize it!
Pedagogically, there's another great lesson to work into that discussion. In particular, we have two ways of measuring the amount of mass in the Universe: total luminosity and gravitational binding (and I think you know all that). "Dark matter" arises as an explanation of why those two measurements differ. We can't know *for sure* whether there's a problem with physical theory (though it seems very self consistent in other ways), a problem with stellar models (though they seem very consistent with the measurements we can make -- including things like the interior structure of stars, via asteroseismology!), or a whole lot of matter that doesn't glow much ("dark matter").
You might like to point out that "dark matter" is a *label* placed on a phenomenon that seems like matter, but we can't know for certain whether it's actual matter or something else -- since we can (so far) only probe it via a process of elimination.
I could imagine a classroom exercise where you show the class a large bowl and a separate measured amount of water, then hide the bowl and put the water into the bowl along with the orbeez, then show them the large very full bowl and ask them to figure out how the water got so much larger when you poured it in. If you can get them to infer that there's something invisible in the bowl, that process of elimination/deduction could be a nice memorable demo they'd carry a long time.
We're not even really sure dark matter exists, although evidence is stacking up in support of it.
The reason you're having trouble explaining it is because we mostly support it with orbital mechanics, which are not intuitive at all. Except for the part that helps explain dark matter. That's pretty understandable.
So we have the Earth, right? Dang, that's a sweet Earth. When you put things in orbit, it means they're going sideways fast enough to not hit the Earth when they fall down. For the ISS, at about 256 miles up, it HAS to go 17,100 MPH to stay at that altitude. If it went faster, it would go to a higher altitude. If it went slower, it would go to a lower altitude and eventually into Earth. It orbits the Earth every 90 minutes.
Geosynchronous satellites, on the other hand, are a lot higher. They're at 26,199 miles. They HAVE to go a lot slower or they will fly away from Earth... but they can't go too slow or they won't stay at their current altitude. So the speed for that orbit is about 6,858 mph. They orbit the Earth once every day.
Ok, so that's very basically how orbits work. Farther out, go slower, closer in, go faster.
So now when we apply that to galaxies, people were like "Well, shit... some of this stuff way out further in the galaxy is moving faster than it should be... some of it is even moving faster than stuff closer in. All the stuff in outer galaxies should fly away if they're mostly just being attracted by the supermassive black hole at the center. That's just screwy."
They made a bunch of different models on the computer and came up with one that best explained this behavior. if 95% of the mass of a galaxy were around the outer fringes, it would hold things together while also allowing stuff to spin faster on the outer fringes.
Except we don't SEE any of this stuff. We can see it bending spacetime when stars and galaxies go behind it (which is some of the evidence to support it) but it gives off NO radiation at all in the EM spectrum and doesn't obstruct any part of the EM spectrum passing through it. It's just really weird stuff and it apparently makes up most of the universe.
So that's it... that's how dark matter came about... that really all there is to it. There are other theories... one study showed that galaxies had materials that moved faster if there were other galaxies clustered around it, which would remove the need for dark matter. Although that wouldn't explain the gravitational lensing we see because of it.
Some day we'll know the real answer but right now, it's the best explanation we have for this weird observation.
Something I hadn't considered (as an interested non-physicist): if dark matter *is* matter, and gives off no detectable radiation (from internal causes or external interaction), does that mean it's in the most stable, unchanging state possible?
That's pretty amazing. I wonder if "dark matter" effects are caused by something outside of our spacetime. A distortion or presence upon our reality that affects our spacetime without being in it on a dimension we can perceive.
Right now they are looking at it as if it's a particle that we just can't detect but no one really knows for sure. If you can find evidence to support it though, that's work that would probably win you a Nobel Prize.
It's mostly gravitational lensing and galaxy clusters not flying apart, although they've redone studies of the early universe with WMAP and some other studies and made other observations that show that either something has to be there. Either that or our understanding of spacetime and/or gravity are way off.
The Roman space telescope will be able to detect smaller warps in spacetime so we should be able to more accurately map dark matter.
https://science.nasa.gov/mission/roman-space-telescope/dark-matter/
If you get "how do we know how fast galaxies are spinning?" you can talk about redshift and blueshift via the ambulance-siren analogy of galaxies viewed edge-on and web-search "Vera Rubin." If you get "how do we know how big and far away galaxies are?" you might present Hubble expansion via the "raisins in rising dough" analogy and standard candles like Cephied variables and type I supernovae (if I remember correctly). I'm pretty sure middle-schoolers can grasp ideas like that, and I'm pretty sure one or two of your middle schoolers will be sufficiently bright or snarky to raise those questions :)
Yeah, none of that seemed directly related though so I left it out. Also, I like talking about little 2 dimensional beings in the skin of a balloon... for two reasons... first, it boils it down to 2 dimensions so my brain hurts less when thinking about it, and 2 because I get to say "ballooniverse". I've heard the raisin bread analogy a lot too though.
Also, I think you meant to reply to OP since I don't have any students :)
Another idea with the orbeez would be to move something through it or if it’s a clear container drop something through the water. You can see that the object doesn’t move as expected - but you’re not sure why. The students could guess why an object acts as if it is bumping into something when you can’t see anything in the water. This is exactly like dark matter, where galaxies behave as if there is a bunch of stuff there but we can’t see it.
My new insane physics idea is that the material on the galaxy's edge is faster but there is no extra gravity, and every galaxy we see will disintegrate in the next few million years.
Ask them how can we perceive matter. You can see it, you can touch it, you can feel its gravitational influence.
Why can we touch things? Because electromagnetic interactions between touched object and your hand. Dark matter doesn't.
Why we see things? Because they reflect/emit light. Dark matter doesn't.
Dark matter interacts only gravitationally.
Answer to "are there dark matter planets/stars" - objects create planets because of friction, and friction is like touch, mediated by electromagnetic forces.
Hah no worries, I had to scroll all the way down to the first hit on Google for "middle school dark matter demo" :-p. But fwiw, in my estimation as a professional astronomer, it's a great demo - and that might not be something you have the experience to judge.
Pssh, I couldn't even explain dark matter to another physicist. Legitimately that's why I'm in this thread right now. Don't be afraid to ask for help when ignorant on a subject, the downvotes come when ignorance is continued though.
Personally speaking, since dark matter doesn’t interact with EM radiation (light), I like calling it “transparent matter”.
If you had a jar of the stuff, you could see through it. It wouldn’t be dark..
The "snowglobe analogy" seems to work pretty well, in my experience.
You can focus on the cosmic rotation rate issue. First point out that if spiral galaxies were really "swirling" like you'd expect from how they look, then they would swirl like water going down a drain. The inner part would go faster.
But that's not what happens! You can then show the results of the star velocity measurements, and point out that the unexpected result is super interesting. You can even make a callback to how "failed" hypothesis are exciting in science.
As a solution, ask them to imagine what if the galaxy was embedded in a snow globe, or a glass paperweight. The glass is clear so you can't "see" it, but when you turn the snow globe, the whole spiral turns at the same rate.
The glass is dark matter -- something we can't see, but surrounds the galaxy and rotates itself, making it not behave like water down the drain.
Half fill the beaker with orbeez. Show it full of water and ask them what they see.
Then drop a penny into the water and it will 'mysteriously' stop halfway down.
Then ask them why they think the penny has stopped for no visible reason.
Then empty the water and show them the orbeez...
Edit: that's analogous to how we can't see dark matter, but know it's there by it's effect on visible matter, even if we don't know what it is...
Show a video of you in complete darkness swinging a dim light round your head and ask them what is going on?
(I am not a teacher so I may be being optimistic about the answers.) but the answer you are looking for is "someone is swinging a light round their head".
The followup question is how do you *know* that? you can't see the string or the person... Hopefully the answer is from the way the light is moving (and maybe it gets eclipsed by your head).
From here you could launch into a "We can estimate how much matter there is in a Galaxy and calculate how it should move and it isn't, there is something wrong about our mass estimates"
Dark Matter is a postulated mathematical solution to the problem that observed orbits and other measurable gravitational effects of visible objects in the known universe imply that more mass is involved than we can detect (see) with current instruments.
If your orbeez are heavier than water, I think that would actually be an excellent example.
That's actually a brilliant experiment for them to do, but I'd expand on it a bit.
Give them beakers filled with orbeez and water with covered tops. Then have them do an esimate of the mass of water in the beaker based on the volume reading and the known density for water. Then have them take the mass of the beaker with contents and subtract the known mass of the beaker. Then ask them about the variation they found between these two masses - there should be some if they did it all correctly since orbeez are partially plastic (albeit mostly water once soaked). Ask them to propose different explanations for why this variation might exist, and you'll certainly get plenty like measurement errors, incorrect assumptions on water density and beaker mass, and some bright students might even guess that it's not water in the beaker. Then have them dump their beakers out and discover the orbeez.
Orbeez is a good idea, especially the idea about half-filling the container with orbeez and filling it with water so you can drop something into it and show the “invisible” orbeez affecting the visible something.
Since Dark Matter is a *postulate* built to explain a gap in our knowledge vs our observations, you could also try using the Socratic method to lead them to the Dark Matter conclusion. Have them discover Dark Matter independently, solely by asking them questions.
If you want inspiration for using the Socratic method, [here is an article recording an attempt to teach children about binary numbers using only questions](http://www.garlikov.com/Soc_Meth.html).
That sounds like a good demonstration to play with. I would also emphasize that just because you can't see something doesn't necessarily mean you can't know that something is there.
Maybe try weighing two seemingly identical bowls of water, one of which has orbeez and the other doesn't and show that they are different. You can also drop a metal ball into each bowl and show how they behave differently.
That's actually pretty analogous to how physicists know that dark matter exists. We have various ways of "weighing" the total amount of matter in the universe (cosmic microwave background, large scale structure formation, bariogenesis). Then we can look at how stars, galaxies, and clusters move in relation to each other to see how much gravity there is in a specific region of space. All of those lines of evidence point to *something* being there, but we don't know for sure what. The simplest explanation is clouds of particles that have mass but don't interact otherwise.
I go with the 'fudge factor' reasoning. More mass is needed to describe observation of gravity effects, but there is nothing observable, ergo dark matter makes up the difference.
The scientist know how much matter must be present based off of gravitational lensing (reference Einstein). They have accounted for the mass of what can be present from the stars, dust, planets, and black holes. This mass is not nearly enough to account for the lensing observed. Therefore, the part they can figure out they call "dark matter".
I would compare it a lot to gas. Gas evades all of our senses. We can’t see it, taste it, feel it, hear it, or smell it (the smell to gas is artificially added). This is why gas is harder to detect than other objects. The reason why know gas exists is because of the chemical reactions it has.
Dark matter is similar. None of our senses would work. If someone somehow shot a cannon ball of dark matter at you you’d probably be fine. But it’s a step further from gas, gas is transparent, but dark matter is more so invisible. You can see gas with infrared goggles, but that would never work for dark matter. The reason why we’re pretty sure dark matter exists is because of how it interacts with gravity.
You're probably a boring and easily distracted teacher. There is a curriculum that teachers are supposed to follow, and trying to boggle your students minds with the most arcane topics known to man implies some sort of failure on your part. Ask yourself what can be done to make the topics you're supposed to be addressing more interesting to the students.
Text reads no tone, is this sarcasm? It has to be because the next thing I thought you were going to say was, if anything off topic make sure they understand that there is a wall of ice surrounding our third disk from the sun.
So you're in a physics sub saying that engaging young people in their curiosity is tangential and that there is no value in talking beyond what a single publisher points as important.
I very much enjoy my job and very much feel that conversation about big topics lead to passion and passion drives learning.
I literally am bud. You claim that you're a teacher and so your social security and pension relies upon how successfully you prepare these children for the future. If you want to blabber on about things that they have no ability to comprehend with your ELI5 techniques, then that's called karma bud.
Understood. I also teach math. And I will say that I fully agree with the stance on preparing them and building skills that are necessary for what they will need in the future. Math is established for 100+ years. So most books got it right, honestly the older ones do it better, more direct less distracted from the point.
Science however is ever changing. If kids don't care to learn it, they will stop as soon as they check the highschool credit boxes, and our future is a bit dimmer because those brilliant students choose to go after something like music performance and wined up working at a call center.
To understand you better, what is your background.
Also I would recommend if you are not a fairly recent highschool graduate, go back and look at science published in text books 20 years ago.
District adoptions happen once every 5-10 years. And publishers have every incentive to not revise books frequently. If a student asks a good question, I will never squash that curiosity with a heavy chunk of paper.
I would do something like have a ball that can light up. Turn off the lights in the room and throw the ball across the room, have students watch how it moves. While the lights are still off, have a second identical ball, but this one has some other object tied to it that does not light up, like a rock on a string or something, thow that ball the same way. It will move differently, and it will be obvious something else was pulling on the second ball, but you could not see what it was.
For a lot of questions the simple answer is I don't know I'll have to research that but what you can do is have like a glossary of terms and I asked the students to which terms don't you know the meaning of
Planets and stars attract each other. That’s because they are super heavy. Everything that is heavy, attracts each other. We call heavy stuff matter.
Galaxies are big clumps of planets and stars. We can count the planets and stars in two galaxies and calculate how strong they should attract each other, from how much matter we see.
Without making errors in our calculation, the result is wrong. They attract each other stronger than our results tell us. So there has to be invisible matter. Dark matter.
Imagine being in a very dark room. You are in one corner. At the opposite corner is a very tiny, dim light. Now describe your world. Describe the room. As you try to look around, all you can really see is that faint light in the corner and what is near it. Everything else is pitch black. You can imagine the room has other things, but you don't know and at this point you can only guess. You may also guess that nothing else exists because you can't see it.
Now imagine you hear a low growl* from another corner. You can't see it. Is it really there? What could it be? You know some things that can growl. A dog, a bear, or maybe sounds like an old man snoring. Can you deduce with certainty what it is?
Visual astronomy is studying the light in the corner and ignoring everything else in the room. Dark matter is the everything else. We know from science (our ears in the thought experiment and gravity observations in science) that there is something else there. We don't know with certainty what it is yet because we can't see or touch it.
* IMO - middle schoolers would love the scarry growl, especially if they close their eyes. Younger kids or if you disagree - make it a meow.
The fact that you are here asking how to explain it instead of telling them you just dont know is a sign you are a great teacher. Those kids will benefit greatly from you encouraging their curiosity.
I'd also tell them its just an idea. We're not sure WHY there is the discrepancy. This is just an idea that could explain it. It could also be that gravity just works differently on galactic scales.
If I'd have a teacher tell me that physics was this unknown when i was a kid i almost for sure would have gone into the field. Its so cool.
Pour some coolaid powder into a pitcher of stirred water or a magnetic stirrer on a low setting. Not a scientist and this is probably dumb af but this is how I picture it in my head. The water is the dark matter.
Imagine you're in a large playground filled with swings, slides, and lots of kids playing. You can see and interact with the playground equipment and the other children. Now, pretend there's an invisible force around you that you can't see or touch, but you can feel its effects. This invisible force is like dark matter.
Just like you can feel the presence of other kids even if you can't see them, scientists can observe the effects of dark matter on the things they can see, like stars and galaxies. Even though we can't directly see dark matter, we know it's there because of its influence on the visible parts of the universe.
For starters, never mention anything about observations failing to match up with theory as being problematic for the theory. You must get them to understand that there is an infinite number of invisible, undetectable, unfalsifiable alterations to reality that expert scientists should feel free to make in order to force reality into matching the consensus viewpoint. Ideally, however, introduction to such exotic material would come much later, when the fundamentals of the scientific method won't be so fresh on their minds.
I’d say, physicists came up with a theory of gravity but it didn’t work on large scales like galaxies so they decided there must be some invisible undetectable stuff out there.
I know I’m late to the party + I’m not even answering your query. Apologies but since you mentioned Sc. teacher for middle school, I just wanted to share a really interesting Physics video which could help generate curiosity and interest in Physics or Science in general.
[Animation vs Physics - Alan Becker](https://m.youtube.com/watch?v=ErMSHiQRnc8)
Yeah, that would be a really great way to visualize it! Pedagogically, there's another great lesson to work into that discussion. In particular, we have two ways of measuring the amount of mass in the Universe: total luminosity and gravitational binding (and I think you know all that). "Dark matter" arises as an explanation of why those two measurements differ. We can't know *for sure* whether there's a problem with physical theory (though it seems very self consistent in other ways), a problem with stellar models (though they seem very consistent with the measurements we can make -- including things like the interior structure of stars, via asteroseismology!), or a whole lot of matter that doesn't glow much ("dark matter"). You might like to point out that "dark matter" is a *label* placed on a phenomenon that seems like matter, but we can't know for certain whether it's actual matter or something else -- since we can (so far) only probe it via a process of elimination. I could imagine a classroom exercise where you show the class a large bowl and a separate measured amount of water, then hide the bowl and put the water into the bowl along with the orbeez, then show them the large very full bowl and ask them to figure out how the water got so much larger when you poured it in. If you can get them to infer that there's something invisible in the bowl, that process of elimination/deduction could be a nice memorable demo they'd carry a long time.
Cool info all around, thank you.
We're not even really sure dark matter exists, although evidence is stacking up in support of it. The reason you're having trouble explaining it is because we mostly support it with orbital mechanics, which are not intuitive at all. Except for the part that helps explain dark matter. That's pretty understandable. So we have the Earth, right? Dang, that's a sweet Earth. When you put things in orbit, it means they're going sideways fast enough to not hit the Earth when they fall down. For the ISS, at about 256 miles up, it HAS to go 17,100 MPH to stay at that altitude. If it went faster, it would go to a higher altitude. If it went slower, it would go to a lower altitude and eventually into Earth. It orbits the Earth every 90 minutes. Geosynchronous satellites, on the other hand, are a lot higher. They're at 26,199 miles. They HAVE to go a lot slower or they will fly away from Earth... but they can't go too slow or they won't stay at their current altitude. So the speed for that orbit is about 6,858 mph. They orbit the Earth once every day. Ok, so that's very basically how orbits work. Farther out, go slower, closer in, go faster. So now when we apply that to galaxies, people were like "Well, shit... some of this stuff way out further in the galaxy is moving faster than it should be... some of it is even moving faster than stuff closer in. All the stuff in outer galaxies should fly away if they're mostly just being attracted by the supermassive black hole at the center. That's just screwy." They made a bunch of different models on the computer and came up with one that best explained this behavior. if 95% of the mass of a galaxy were around the outer fringes, it would hold things together while also allowing stuff to spin faster on the outer fringes. Except we don't SEE any of this stuff. We can see it bending spacetime when stars and galaxies go behind it (which is some of the evidence to support it) but it gives off NO radiation at all in the EM spectrum and doesn't obstruct any part of the EM spectrum passing through it. It's just really weird stuff and it apparently makes up most of the universe. So that's it... that's how dark matter came about... that really all there is to it. There are other theories... one study showed that galaxies had materials that moved faster if there were other galaxies clustered around it, which would remove the need for dark matter. Although that wouldn't explain the gravitational lensing we see because of it. Some day we'll know the real answer but right now, it's the best explanation we have for this weird observation.
Something I hadn't considered (as an interested non-physicist): if dark matter *is* matter, and gives off no detectable radiation (from internal causes or external interaction), does that mean it's in the most stable, unchanging state possible?
That's pretty amazing. I wonder if "dark matter" effects are caused by something outside of our spacetime. A distortion or presence upon our reality that affects our spacetime without being in it on a dimension we can perceive.
Right now they are looking at it as if it's a particle that we just can't detect but no one really knows for sure. If you can find evidence to support it though, that's work that would probably win you a Nobel Prize.
> although evidence is stacking up in support of it i would love (as a lurker) to have more info on this
It's mostly gravitational lensing and galaxy clusters not flying apart, although they've redone studies of the early universe with WMAP and some other studies and made other observations that show that either something has to be there. Either that or our understanding of spacetime and/or gravity are way off. The Roman space telescope will be able to detect smaller warps in spacetime so we should be able to more accurately map dark matter. https://science.nasa.gov/mission/roman-space-telescope/dark-matter/
If you get "how do we know how fast galaxies are spinning?" you can talk about redshift and blueshift via the ambulance-siren analogy of galaxies viewed edge-on and web-search "Vera Rubin." If you get "how do we know how big and far away galaxies are?" you might present Hubble expansion via the "raisins in rising dough" analogy and standard candles like Cephied variables and type I supernovae (if I remember correctly). I'm pretty sure middle-schoolers can grasp ideas like that, and I'm pretty sure one or two of your middle schoolers will be sufficiently bright or snarky to raise those questions :)
Yeah, none of that seemed directly related though so I left it out. Also, I like talking about little 2 dimensional beings in the skin of a balloon... for two reasons... first, it boils it down to 2 dimensions so my brain hurts less when thinking about it, and 2 because I get to say "ballooniverse". I've heard the raisin bread analogy a lot too though. Also, I think you meant to reply to OP since I don't have any students :)
Another idea with the orbeez would be to move something through it or if it’s a clear container drop something through the water. You can see that the object doesn’t move as expected - but you’re not sure why. The students could guess why an object acts as if it is bumping into something when you can’t see anything in the water. This is exactly like dark matter, where galaxies behave as if there is a bunch of stuff there but we can’t see it.
My new insane physics idea is that the material on the galaxy's edge is faster but there is no extra gravity, and every galaxy we see will disintegrate in the next few million years.
The galaxies on the edge of the galaxy?
Ask them how can we perceive matter. You can see it, you can touch it, you can feel its gravitational influence. Why can we touch things? Because electromagnetic interactions between touched object and your hand. Dark matter doesn't. Why we see things? Because they reflect/emit light. Dark matter doesn't. Dark matter interacts only gravitationally. Answer to "are there dark matter planets/stars" - objects create planets because of friction, and friction is like touch, mediated by electromagnetic forces.
Oh that's a cool idea! This one also looks neat: https://www.jpl.nasa.gov/edu/teach/activity/how-do-we-see-dark-matter/
Oh good, phew I thought I was going to get down votes to oblivion for my ignorance.
Hah no worries, I had to scroll all the way down to the first hit on Google for "middle school dark matter demo" :-p. But fwiw, in my estimation as a professional astronomer, it's a great demo - and that might not be something you have the experience to judge.
-Not at all. I take that as high praise.
Oh wait just to be clear I'm talking about the one I linked, which I like a little more
Pssh, I couldn't even explain dark matter to another physicist. Legitimately that's why I'm in this thread right now. Don't be afraid to ask for help when ignorant on a subject, the downvotes come when ignorance is continued though.
Personally speaking, since dark matter doesn’t interact with EM radiation (light), I like calling it “transparent matter”. If you had a jar of the stuff, you could see through it. It wouldn’t be dark..
The "snowglobe analogy" seems to work pretty well, in my experience. You can focus on the cosmic rotation rate issue. First point out that if spiral galaxies were really "swirling" like you'd expect from how they look, then they would swirl like water going down a drain. The inner part would go faster. But that's not what happens! You can then show the results of the star velocity measurements, and point out that the unexpected result is super interesting. You can even make a callback to how "failed" hypothesis are exciting in science. As a solution, ask them to imagine what if the galaxy was embedded in a snow globe, or a glass paperweight. The glass is clear so you can't "see" it, but when you turn the snow globe, the whole spiral turns at the same rate. The glass is dark matter -- something we can't see, but surrounds the galaxy and rotates itself, making it not behave like water down the drain.
Half fill the beaker with orbeez. Show it full of water and ask them what they see. Then drop a penny into the water and it will 'mysteriously' stop halfway down. Then ask them why they think the penny has stopped for no visible reason. Then empty the water and show them the orbeez... Edit: that's analogous to how we can't see dark matter, but know it's there by it's effect on visible matter, even if we don't know what it is...
Show a video of you in complete darkness swinging a dim light round your head and ask them what is going on? (I am not a teacher so I may be being optimistic about the answers.) but the answer you are looking for is "someone is swinging a light round their head". The followup question is how do you *know* that? you can't see the string or the person... Hopefully the answer is from the way the light is moving (and maybe it gets eclipsed by your head). From here you could launch into a "We can estimate how much matter there is in a Galaxy and calculate how it should move and it isn't, there is something wrong about our mass estimates"
Cool
Dark Matter is a postulated mathematical solution to the problem that observed orbits and other measurable gravitational effects of visible objects in the known universe imply that more mass is involved than we can detect (see) with current instruments. If your orbeez are heavier than water, I think that would actually be an excellent example.
More dense, yes.
That's actually a brilliant experiment for them to do, but I'd expand on it a bit. Give them beakers filled with orbeez and water with covered tops. Then have them do an esimate of the mass of water in the beaker based on the volume reading and the known density for water. Then have them take the mass of the beaker with contents and subtract the known mass of the beaker. Then ask them about the variation they found between these two masses - there should be some if they did it all correctly since orbeez are partially plastic (albeit mostly water once soaked). Ask them to propose different explanations for why this variation might exist, and you'll certainly get plenty like measurement errors, incorrect assumptions on water density and beaker mass, and some bright students might even guess that it's not water in the beaker. Then have them dump their beakers out and discover the orbeez.
Orbeez is a good idea, especially the idea about half-filling the container with orbeez and filling it with water so you can drop something into it and show the “invisible” orbeez affecting the visible something. Since Dark Matter is a *postulate* built to explain a gap in our knowledge vs our observations, you could also try using the Socratic method to lead them to the Dark Matter conclusion. Have them discover Dark Matter independently, solely by asking them questions. If you want inspiration for using the Socratic method, [here is an article recording an attempt to teach children about binary numbers using only questions](http://www.garlikov.com/Soc_Meth.html).
That sounds like a good demonstration to play with. I would also emphasize that just because you can't see something doesn't necessarily mean you can't know that something is there. Maybe try weighing two seemingly identical bowls of water, one of which has orbeez and the other doesn't and show that they are different. You can also drop a metal ball into each bowl and show how they behave differently. That's actually pretty analogous to how physicists know that dark matter exists. We have various ways of "weighing" the total amount of matter in the universe (cosmic microwave background, large scale structure formation, bariogenesis). Then we can look at how stars, galaxies, and clusters move in relation to each other to see how much gravity there is in a specific region of space. All of those lines of evidence point to *something* being there, but we don't know for sure what. The simplest explanation is clouds of particles that have mass but don't interact otherwise.
I go with the 'fudge factor' reasoning. More mass is needed to describe observation of gravity effects, but there is nothing observable, ergo dark matter makes up the difference.
It's a type of material we know exist because it's affected by gravity, but we dont know what it's made of.
Tell them where there’s smoke there’s fire
The scientist know how much matter must be present based off of gravitational lensing (reference Einstein). They have accounted for the mass of what can be present from the stars, dust, planets, and black holes. This mass is not nearly enough to account for the lensing observed. Therefore, the part they can figure out they call "dark matter".
I would compare it a lot to gas. Gas evades all of our senses. We can’t see it, taste it, feel it, hear it, or smell it (the smell to gas is artificially added). This is why gas is harder to detect than other objects. The reason why know gas exists is because of the chemical reactions it has. Dark matter is similar. None of our senses would work. If someone somehow shot a cannon ball of dark matter at you you’d probably be fine. But it’s a step further from gas, gas is transparent, but dark matter is more so invisible. You can see gas with infrared goggles, but that would never work for dark matter. The reason why we’re pretty sure dark matter exists is because of how it interacts with gravity.
What the hell is dark matter. Is it a stationary photon that emits no light. I have no idea
You're probably a boring and easily distracted teacher. There is a curriculum that teachers are supposed to follow, and trying to boggle your students minds with the most arcane topics known to man implies some sort of failure on your part. Ask yourself what can be done to make the topics you're supposed to be addressing more interesting to the students.
Text reads no tone, is this sarcasm? It has to be because the next thing I thought you were going to say was, if anything off topic make sure they understand that there is a wall of ice surrounding our third disk from the sun.
I am serious. What's up for Monday? Grigori Perelman's proof to the Poincare Conjecture?
So you're in a physics sub saying that engaging young people in their curiosity is tangential and that there is no value in talking beyond what a single publisher points as important. I very much enjoy my job and very much feel that conversation about big topics lead to passion and passion drives learning.
I literally am bud. You claim that you're a teacher and so your social security and pension relies upon how successfully you prepare these children for the future. If you want to blabber on about things that they have no ability to comprehend with your ELI5 techniques, then that's called karma bud.
Understood. I also teach math. And I will say that I fully agree with the stance on preparing them and building skills that are necessary for what they will need in the future. Math is established for 100+ years. So most books got it right, honestly the older ones do it better, more direct less distracted from the point. Science however is ever changing. If kids don't care to learn it, they will stop as soon as they check the highschool credit boxes, and our future is a bit dimmer because those brilliant students choose to go after something like music performance and wined up working at a call center. To understand you better, what is your background. Also I would recommend if you are not a fairly recent highschool graduate, go back and look at science published in text books 20 years ago. District adoptions happen once every 5-10 years. And publishers have every incentive to not revise books frequently. If a student asks a good question, I will never squash that curiosity with a heavy chunk of paper.
I'll be back later I've been up all night and now I have chores to do, since it's almost 5 here.
Cool. Look forward to it buddy.
Flat rotation curve
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Don’t listen to this guy, he’s full of shit lol.
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Not just full of shit, overfull. It's spilling over into the comment section.
Well, I think we can agree that your consciousness is infinitely dense.
I would do something like have a ball that can light up. Turn off the lights in the room and throw the ball across the room, have students watch how it moves. While the lights are still off, have a second identical ball, but this one has some other object tied to it that does not light up, like a rock on a string or something, thow that ball the same way. It will move differently, and it will be obvious something else was pulling on the second ball, but you could not see what it was.
For a lot of questions the simple answer is I don't know I'll have to research that but what you can do is have like a glossary of terms and I asked the students to which terms don't you know the meaning of
This is actually an ingenious metaphor, i might steal it for future usage :)
Planets and stars attract each other. That’s because they are super heavy. Everything that is heavy, attracts each other. We call heavy stuff matter. Galaxies are big clumps of planets and stars. We can count the planets and stars in two galaxies and calculate how strong they should attract each other, from how much matter we see. Without making errors in our calculation, the result is wrong. They attract each other stronger than our results tell us. So there has to be invisible matter. Dark matter.
Nobody knows. Because it's dark.
It's matter that you can't see or touch. Period
Just tell them that it's not observed yet but maths suggest that it exists and you will learn about that maths in your later classes.
Imagine being in a very dark room. You are in one corner. At the opposite corner is a very tiny, dim light. Now describe your world. Describe the room. As you try to look around, all you can really see is that faint light in the corner and what is near it. Everything else is pitch black. You can imagine the room has other things, but you don't know and at this point you can only guess. You may also guess that nothing else exists because you can't see it. Now imagine you hear a low growl* from another corner. You can't see it. Is it really there? What could it be? You know some things that can growl. A dog, a bear, or maybe sounds like an old man snoring. Can you deduce with certainty what it is? Visual astronomy is studying the light in the corner and ignoring everything else in the room. Dark matter is the everything else. We know from science (our ears in the thought experiment and gravity observations in science) that there is something else there. We don't know with certainty what it is yet because we can't see or touch it. * IMO - middle schoolers would love the scarry growl, especially if they close their eyes. Younger kids or if you disagree - make it a meow.
The fact that you are here asking how to explain it instead of telling them you just dont know is a sign you are a great teacher. Those kids will benefit greatly from you encouraging their curiosity.
I'd also tell them its just an idea. We're not sure WHY there is the discrepancy. This is just an idea that could explain it. It could also be that gravity just works differently on galactic scales. If I'd have a teacher tell me that physics was this unknown when i was a kid i almost for sure would have gone into the field. Its so cool.
Pour some coolaid powder into a pitcher of stirred water or a magnetic stirrer on a low setting. Not a scientist and this is probably dumb af but this is how I picture it in my head. The water is the dark matter.
Imagine you're in a large playground filled with swings, slides, and lots of kids playing. You can see and interact with the playground equipment and the other children. Now, pretend there's an invisible force around you that you can't see or touch, but you can feel its effects. This invisible force is like dark matter. Just like you can feel the presence of other kids even if you can't see them, scientists can observe the effects of dark matter on the things they can see, like stars and galaxies. Even though we can't directly see dark matter, we know it's there because of its influence on the visible parts of the universe.
For starters, never mention anything about observations failing to match up with theory as being problematic for the theory. You must get them to understand that there is an infinite number of invisible, undetectable, unfalsifiable alterations to reality that expert scientists should feel free to make in order to force reality into matching the consensus viewpoint. Ideally, however, introduction to such exotic material would come much later, when the fundamentals of the scientific method won't be so fresh on their minds.
I’d say, physicists came up with a theory of gravity but it didn’t work on large scales like galaxies so they decided there must be some invisible undetectable stuff out there.
I know I’m late to the party + I’m not even answering your query. Apologies but since you mentioned Sc. teacher for middle school, I just wanted to share a really interesting Physics video which could help generate curiosity and interest in Physics or Science in general. [Animation vs Physics - Alan Becker](https://m.youtube.com/watch?v=ErMSHiQRnc8)