Video by: PBS
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http://www.pbs.org/nova/sciencenow We can't see dark matter, and some skeptics doubt its existence, but many scientists think it makes up 20-some percent of our universe. Astronomer Doug Clowe explains how the Bullet Cluster, a group of galaxies billions of light years away, may shed some light on this mysterious stuff.
Don't miss the new season of NOVA scienceNOW, airing every Wednesday at 9pm starting June 25 on PBS. Watch past episodes of the program, try out interactives, and more on our Web site: http://www.pbs.org/nova/sciencenow

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Tags: astronomy astrophysic bullet clowe cluster cosmic dark doug galaxy matter nova pbs science  nova sciencenow | the dark matter mystery | pbs See more videos uploaded by PBS

Comments for this video on YouTube

So, instead of ... ( 3 months ago by moulingalette)

So, instead of saying that our models of gravity may not be completely accurate for all scales (they don't seem to work at the galaxy size), we postulate matter that we cannot see. Nice.

all matter has ... ( 3 months ago by squirrelsivertsen)

all matter has gravity (i agree) but all gravity isnt from matter. do u agree? Because black holes have gravity,& a black hole isnt matter. soo they know dark matter exists because of the extra gravity.... & i think this extra gravity is just black holes.

LOL!!!!!!!!!!!! ( 2 months ago by tall32guy)

LOL!!!!!!!!!!!!

um black holes do ... ( 2 months ago by PingerNz)

um black holes do have mass. A LOT of mass. scrunched down to a single point called a singularity. The mass does exist though

Yes it used to be ... ( 2 months ago by 7July2008)

Yes it used to be huge planets but they have been squished down real small

lol dark matter is ... ( 2 months ago by yamilink03)

lol dark matter is to physics as god is to religion, i personally find dark matter funny. its mocking us! "hey guys i exist because i do this....but you cant find meeeee he he he"

Aren't planets a ... ( 2 months ago by kemz1969)

Aren't planets a type of "dark matter"? Planets don't give off light. Or is that too much?? So - maybe there are some proto-planets not orbiting anything - maybe they're materials that cannot be seen as they have not come in contact with light -- they could be part of the dark matter myster - matter that exists but does not give off or reflect light ..

Surely the ... ( 2 months ago by thegreenhammer)

Surely the supermassive black holes that are predicted to be in the centre of each galaxy would add a huge amount of mass (maybe an even unexpectedly large amount)to a galaxy? They say that our galaxy is spinning about its centre, much like how the planets orbit the sun (ie held in place by gravity). Id take it that the sun hold most of the mass within our solar system, so why isn't it the same for a black hole in the centre of galaxy? (only that it is a singularity due to its own mass)

lol i saw 1 of the ... ( 2 months ago by xsararangerpkerx)

lol i saw 1 of the scientist there on discovery channel's Naked Science, he was talking about pluto lol

1first we need to ... ( 2 months ago by circle559)

1first we need to distinguish the difference between mass and matter. matter consist of two mass with one spinning around the other in two ways at the sametime, causing a spherical force outward ( centrifugal). this outwardforce is what pushes against our fingers so we can touch matter. this force act like a wall. this wall is the wall that light bounces from and reflect. the deacceleration and acceleration of the mass in motion creates heat and light thus matter can emmit light. mass is just a

Another dumbed down ... ( 2 months ago by DoorwayToHeaven)

Another dumbed down PBS/NOVA program, starring the same people with the same opinion, and which gets it all wrong. Hey, PBS, its not 20% but 80-90% of the universe which has not been detected. If they can't even get this right, why bother. Face it, when it comes to science and history, PBS can't be trusted. For real science I recommend the Sarastarlight channel which gets a heck of a lot more views than this dumbed down PBS channel.

LOL. You guys ... ( 2 months ago by DoorwayToHeaven)

LOL. You guys censor comments? They have to be preapproved first? Total dishonesty. No integrity. You create programs filled with mistakes and then you prevent anyone from pointing out the errors. Typical PBS--Propaganda and BS. How pathetic. What a joke. Ha hahhaha.

I think you've said ... ( 2 months ago by BioNRGy)

I think you've said it the other way around. Mass consists of different manifestations matter (Protons, neutrons etc). This way matter doesnt have to be mass but could somehow have another manifestation that would be dark matter. Cant read what you said after but I liked your comment the most.

you can see the ... ( 2 months ago by topholewhat0)

you can see the fish but you can't see the water is it really that difficult to envisage

Actually, they are ... ( 1 month ago by manster200673)

Actually, they are right...dark matter is estimated to make up 26% of the universe and dark ENERGY (different thing) about 70% percent. Figures per the Chandra Xray center , Harvard.

i just flushed my ... ( 1 month ago by salman497)

i just flushed my dark matter in Toilet :)

O.K. but now, on ... ( 1 month ago by adorianvlad)

O.K. but now, on top of all the constants in the Universe, Dark Matter has to have a certain value in order for life to exist.

not sure whether ... ( 4 weeks ago by siouxziesoo)

not sure whether the bullet cluster argument is really the best to explain dark matter... but this was good nonetheless. a nice way to explain what dark matter 'is.'

Interesting, but ... ( 4 weeks ago by MistressDidi)

Interesting, but these theories are based on 3-dimensional constructs such as we experience on Earth. There is always the possibility that what appears top hold the galaxies together is something completely out of our scope of understanding from a 3D perspective.

I agree...? ( 2 weeks ago by herito87)

I agree...?

good one ( 1 week ago by rcpwnsu)

good one

WARNING: This video ... ( 5 days ago by statickk14)

WARNING: This video is not for creationist morons!!

black hole ... ( 4 days ago by Barbitone)

black hole singularity create torque which creates both gravity and electromagnetism in fractional (fractal) golden ratios

So all the genius ... ( 2 days ago by mccote)

So all the genius physicists are wrong? Care to show your work? We are in a black hole? I didn't get that memo.