Argument why the universe is not isotropic

[jeff Mitchel]

If the universe is isotropic (according to the big bang) then where is the dark matter? It wouldn't appear to be to hard to find as it is supposed to be 95% of all matter. When I drop a pencil it falls to the floor according to the laws of physics, it doesn't fly off to the ceiling or slam into a wall manipulated by unseen stuff. No, no Wimps here in my room.

[insane_alien]

well, the reason it is so difficult to find is because it doesn't really interact with anything except by gravity.

 

and why would it make anything fly off your desk? it obeys the laws of physics too.

 

also, we have seen it indirectly by measuring the gravitational lensing of light moving through patches of darkmatter.

[Realitycheck]

I was about to ask a similar question, mainly what direct evidence do we have that supports dark matter? 95% is a really big number, even if it is scattered among the total abyss. I can see how it would add up. 1 loose baryon per cubic meter of empty space would add up, but I have a hard time seeing how it would have any meaningful effect on gravity or lensing. It seems like the density of dark matter should be greatest surrounding planets and solar systems where it should stand out more, like some probe like Rosetta should be able to scoop some of it up.

[swansont]

Why should a probe be able to scoop it up? Do we have any retrieval methods that exclusively use the gravitational force to capture anything?

 

As for meaningful effect, you have to integrate the distribution over the volume. Space is big.

 

Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

Douglas Adams, The Hitchhiker's Guide to the Galaxy

[thedarkshade]

Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

Douglas Adams, The Hitchhiker's Guide to the Galaxy

I was trying to say something simple that would tell the largeness of space, but I believe there is nothing simpler and more meaningful than this phrase. Thanks Tom!

[jeff Mitchel]

How can dark matter affect the trajectory of stars when it can't even affect the trajectory of my pencil? Gravity is gravity. There should be an effect on my pencil if it is really here.

[thedarkshade]

How can dark matter affect the trajectory of stars when it can't even affect the trajectory of my pencil? Gravity is gravity. There should be an effect on my pencil if it is really here.

Have you ever thought that gravity which dark matter causes might be part of the gravity we feel in our physical world? Like our gravity might actually represent the gravity of 'known matter' and dark matter as well (just assuming)!

[timo]

How can the sun affect the motion of Jupiter when it can't even affect the trajectory of your pencil?

[jeff Mitchel]

The sun is not in my room.

[Klaynos]

The sun is not in my room.

 

And neither is enough dark matter to overcome the mass of the earth.... and if there was a shell around the earth (like an atmosphere) then the gravity inside of it due to the shell would be 0.

[timo]

And neither is there any object in the room that causes the pencil to fall down. Strange world.

[jeff Mitchel]

If 95% of all matter is dark matter then the gravity of the earth should have no effect because it's in the 5% that we can see. Neither should the sun have any effect on Jupiter becuse it too is in the 5%. It seems that dark matter does not live in our neighborhood (nobody has found it yet, and not from lack of trying)and so thus the universe is not isotropic.

[Riogho]

How can dark matter affect the trajectory of stars when it can't even affect the trajectory of my pencil? Gravity is gravity. There should be an effect on my pencil if it is really here.

 

Because there isn't a crapload of dark matter near your pencil.

 

Dark matter tends to be together, knido f like planets.

 

How could the sun have gravity, and affect teh orbit of the planets but not affect your pencil?

 

Because it isn't close to your pencil.

 

Doesn't mean it isn't there, or that it's gravitation is less strong then the earths.

[swansont]

If 95% of all matter is dark matter then the gravity of the earth should have no effect because it's in the 5% that we can see. Neither should the sun have any effect on Jupiter becuse it too is in the 5%. It seems that dark matter does not live in our neighborhood (nobody has found it yet, and not from lack of trying)and so thus the universe is not isotropic.

 

The average matter density in interstellar space is of order a proton per cm^3. So Dark Matter would have an average density of 19 amu per cm^3. Stars and planets are the anomaly as far as density goes.

 

Further, if the dark matter is evenly distributed (or to the extent that it is), there will be no net effect. Gauss's law tells us that the mass outside of a sphere exerts no net force. The gravitational pull is all due to mass inside of the radius of the sphere. So dark matter can affect our orbit about the sun, to the extent that 19 amu/cm^3 can do that. The mass of the sun is 2 x 10^30 kg. The mass of the dark matter at the given density would be more than 15 orders of magnitude smaller in its effect on our orbit about the sun.

[jeff Mitchel]

In response to Riogho, I agree with you, there isn't a "crapload" of dark matter next to my pencil. Thus the universe isn't isotropic. We need to tell all those people wasting time and money looking for WIMPS.

 

In response to Swansont, Gauss's law has to do with electrical field concepts not with gravity.

[Cap'n Refsmmat]

http://en.wikipedia.org/wiki/Gauss's_law#Application_to_gravity

[Realitycheck]

I did see this one incidence of anisotropy pop in the news today, a hole in the universe.

 

The universe, they declared, had a hole in it -- a hole far bigger than anything scientists have ever seen or expected. This "hole" spans almost one billion light years and is six to 10 billion light years from Earth, in the Eridanus constellation [source: Daily Tech].

http://science.howstuffworks.com/hole-in-universe.htm

[kaneda]

Dark matter is described as being either as light as neutrinos or fifty times as heavy as protons. It is said to be 9000.C but radiates no heat. It moves at a constant speed and cannot form small structures but can form very large structures. It is only affected gravitationally and some say most of it is in the galactic halo so why with six times as much matter in the halo as light matter in the rest of the galaxy do galaxies not look like ring doughnuts, with hollow centres?

 

If large structures of DM exist, then moons, planets, stars, neutron stars, black holes would swallow them as they orbit the galaxy and move about within it. Neutron stars and black holes would literally hoover up these large structures leaving almost none left after billions of years. DM should be in moons and every thing larger as well as in the space around us but no evidence.

 

We are told that a small blob in a photo where a solar system sized black hole would be the size of an atom on that scale is proof of DM. We also see computer simulations of DM where unexplained spaces MUST of course be DM. Can it get any worse?

 

agentchange. Amazing. The article shows the structure of the universe is anything but smooth. I find it difficult to believe that another area could drag everything from that area as claimed a possibility.

[John Cuthber]

"How can dark matter affect the trajectory of stars when it can't even affect the trajectory of my pencil? Gravity is gravity. There should be an effect on my pencil if it is really here."

There's half a universe full of dark matter to the left of your pencil. Even given that the density of dark matter is small, half a universefull is a crapload.

However, there's also half a universe to the right of it. It's precisely because the universe is the same on the left side as the right (ie that it's isotropic) that you don't see the pencil fly off sideways.

[jeff Mitchel]

Thank you Kaneda, it appears we are close to being on the same page.

 

John, If half the dark matter is to the left and half to the right, then how come distant stars and galaxies seem to be moved by it.

 

Another thought is how come we do not see the effects of this dark matter in our galaxy or in nearby ones? If it affects only far off galaxies but not close ones then the universe is not isotropic.

[Klaynos]

Thank you Kaneda, it appears we are close to being on the same page.

 

John, If half the dark matter is to the left and half to the right, then how come distant stars and galaxies seem to be moved by it.

 

Because it has a distribution, in the same way other matter does, there is as much normal mass above us, as there is below us (talking radially from the earth in spherical polars) and yet you manage to sit on your chair without floating quite effectively...

 

Another thought is how come we do not see the effects of this dark matter in our galaxy or in nearby ones? If it affects only far off galaxies but not close ones then the universe is not isotropic.

 

Why would only far off galaxies be affected by it?

 

If you are proposing that the universe is not isotropic, you need to provide evidence and also something that is better at predicting things than modern cosmology... GOOD LUCK!

[Martin]

If the universe is isotropic (according to the big bang) then where is the dark matter? It wouldn't appear to be to hard to find as it is supposed to be 95% of all matter. When I drop a pencil it falls to the floor according to the laws of physics, it doesn't fly off to the ceiling or slam into a wall manipulated by unseen stuff. No, no Wimps here in my room.

 

This thread has gone on long enough without any reasonable argument being offered at to why the universe is not isotropic. (that was the theme).

 

Dark energy (about 73 percent) is assume to be absolutely evenly distributed throughout space. this is consistent with isotropy.

 

Matter of all kinds (dark and ordinary) is estimated to be about 27 percent.

We can observe that its distribution is roughly isotropic.

Isotropic means balanced---the same in all directions----more or less.

We clearly see that the density of galaxies, clusters etc, is more or less balanced.

Dark matter is OBSERVED by weak lensing, and MAPPED, and clouds of it coincide rougly with galaxies, clusters of galaxies etc. For all practical purposes, dark matter is distributed just as isotropically as ordinary matter.

 

 

Except for a short comment by Swansont, I did not see any quantitative reasoning in the thread. None of the other discussion seemed to make physics sense.

 

So I am moving the thread to Pseudoscience.

================================

 

Hi Klaynos! Thanks for your comment! I didn't see it when I was writing my post. It looks like you might have similar objections to the pseudo-arguments Mitchel and the like have been offering here. I hope you agree that the thread is pseudo and belongs here.

[Klaynos]

I agree 100% thanks Martin I assumed it already wasn't I hadn't noticed it wasn't!