MACHOS vs WIMPS

Thought <A HREF="http://www.space.com/scienceastronomy/astronomy/dark_matter_011205.html" target="_new"> this </A> was interesting. Anyone for an intelligent discussion?

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Hmmmph--whatever...

I like nachos... does that count?

<b>Bees are on the what now?</b>

This article is a bit too general. A gravitational lens does not magnify anything. What it does is cause mirages or duplicates of the object. In french it's called a gravitational mirage. However, the different duplicates may have different relative magnitudes since each image is not the same age (takes light longer to travel the different paths). Due to the geometry and depending on where the deflecting mass is will determine the number of images. They can also have different red shifts, but their spectral lines will be identical which is how they find them. They were first used to find quasars (according to astronomers I hang around a quasar is a galaxy with a very powerfull source at it's core) and used galaxys as the deflecting mass. What is the deflecting mass that is finding a single star?

A red dwarf? I want to know where in stellar evolution this thing belongs. 10% the mass of the sun would put it in the main sequence or in the same area as a brown dwarf correct? So what's the difference between a red and brown dwarf?

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Self evident ! The color !

Danny

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Although it has a lot of good ideas, beer doesn't know anything about computers!!!

This does NOT prove that light is made of particles and has mass at all.

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No, gravity does not only affect mass. Gravity affects space. Energy must traverse this space, thus, it's path is curved. This is by no means conclusive proof that light has mass. Is the diffraction of light proof that light is a pure wave? No. They are both evidence to show that light has characteristics of a massive particle, and of a massless wave.

Scientifically speaking, mass is determined when the particle is at rest. Photons cannot exist at rest, or (afaik anyways) at any speed below c.

Technically speaking, photons have zero mass. Realistically speaking, photons behave as thought they do have mass, but no <b>proof</b> exists, and any evidence to show it does have mass is balanced out by evidence to show it doesn't.

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Gravity does not directly affect the light. It affects the space through which the light must travel. I wouldn't exactly call that strong evidence... And diffraction is a property of waves. So that suggests outright masslessness.

Eh, either way it's pointless. No one can say anything for sure except for light is messed up

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Alls you got to remember is hot girl = lights on, not hot girl = lights off.

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Great, I'm going to have to get me a can of this "space" stuff and see if it's any good!

What's the frequency, Kenneth?

So, if gravity affects space, what is space? Nominally space is close to a vaccuum, with something like 3 hydrogen molecules per cubic meter or something. So what is space such that awesome gravitational forces can bend it?

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my, we are being very un-secretive lately aren't we?

Okay - two concepts. Space that we have been into is just a place - it is like saying I went to the middle of the Atlantic - just a place. I went to the Moon, I travelled through space to get there. Just like I have to pass through Crewe to gte from London to Glasgow. There isn't very much there but we still have to say we went through it.

Now we have Space. We are talking curving space by extraordinary gravitational forces. We are not talking about affecting Crewe specifically as a place, but more the very fabric of what Crewe is. The whole 3 dimensional schebang so to speak.

So, what is Space?

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First there is no such thing as a vaccume, quantum physics has predicted and they have measured the effects of virtual particles which instantly comeinto existance and anihilate eachother all the time in all empty space.

Bolloks you say? They have measured its effects and it is generally accepted as true. I am waaaay too lazy to provide any linkage, but do a search on quantum physics and virtual particles on google, for papers on the subject.


Secondly, space is not alone, it is SPACETIME, the fabric of which was existin as we speak, and gravity affects this and it has been tested and proven.

Not only does being in a gravity well curve space, it also slows down time(both measured affects) furthermore the faster one travels they curve space(actually flatten it in the direction of motion) and slow time. In fact, if a person is in a room with no windows, and is accelerating in a direction he cannot with any means tell if he is accelerating or under the influence of gravity, their effects are the same.


Many more interesing things about modern physics, get a subscription to scientific american, very very interesting reading.



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I think you could prove that wrong quite easily. If that was the case the moon would be expanding too. We have mirrors set up on the moon that we can beam lasers on to calculate the distance to the moon to within a couple of inches. If we were all expanding those calculations wouldn't work.

Also, the earth doesn't have a reason to expand. It's a solid object with a core that is relatively cool. In order to expand, like an aging star for example, you would need to have a disruption in the balance between differnent forces (thermal, gravitational, etc). When a star runs out of fuel it expands in order to meet the different equilibrium states. When it can't do that calculation show that it collapses on itself within a second and depending on it's mass it ventures down a different stellar evolutionary path.

A terrestrial planet doesn't have a heat source that is radiating out enough to overcome the gravitational well. In order to expand we would have to dismiss gravitational forces, the bending of space time, and the universe as we know it altogether.

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For all I know you might be talking over my head. I never took Condensed Matter Physics. However, the discovery by Hubble that you mentioned I do understand. I just can't think of why you would think that condensed objects would be expanding. It would violate everything from basic Chemistry to complex ideas like Pauli's Exclusion principle which dictates how only one particle can occupy a cube of phase space. Think about the implications of what you are suggesting. They would undermine just about everything.

Take a atom for example. It has a cloud of electrons surrounding it that can become excited and ionized given a quanta of energy. If the space between particles was expanding these values would be changing. That would mean that the fundamental building blocks of the universe would be working on physics that was variable.

How in the world would molecules such as water hold them selves together?

Why would spectra from distant quasars 10 billion years old match spectra from today? Wouldn't the spectra of an element change if the particles were expanding thus using different energies and physical/chemical structures to maintain stability and equilibrium?


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It would mean a complete re-thinking of physics as we understand it, but I still can't think of an example of why it wouldn't work.

The 10 billion year old spectra idea was interesting, but then again, these photons would be travelling through expanding space to get to us. The wavelength of these photons may be stretched as they travel through space that is expanding.

To get a better idea of what I'm talking about, let's make a very simple hydrogen atom out of two balloons (proton and electron). For the sake of simplicity, let's just assume a planet/moon type relationship. Start off with both balloons minimally inflated and a certain distance apart. Now, start blowing up both balloons (matter expansion), and move them apart from each other (space expansion), at a certain rate such that the ratio of the relative dimensions of the electron, proton, and the distance between them are kept constant. Now apply this principle to everything in the universe.

As for the question about the physics of the universe being variable, well isn't that true anyways? Virtual particles being created at random, the increasing success of statistics being used to predict previously believed "constant" phenomena, uncertainty principles... It seems as though constant and static aren't words that go well with physics these days.

I haven't taken condensed matter physics either, but I do enjoy conjecturing .

Again, these aren't necessarily my beliefs, I'm just trying to start an interesting discussion here.

Here's another way to think about it that may explain how the Pauli Principle may not be violated:

Picture a simple molecule, water for example, just sitting in 3D space. Now picture a 3D grid around this molecule so that any point on the molecule can be mapped to a spot on the grid (x,y,z). Now just expand the cube 2x on every axis, and re-map the molecule according to your original coordinates. You now have a molecule that is twice the size, and in the same proportions.

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Damn it LOL I'm never going to go to sleep. Now I have to reply to this

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Oops hehe.

I don't see how the density of an object would change though. Sure the matter is expanding, which would lead to a decrease in density, but then again, the space that the matter is occupying is expanding as well, thus cancelling out that effect.

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We'd have to postulate though that the universe was a spheroid in order for this to work. I'm one of those people who hopes it is some weird shape so that we could warp from one part of the universe to another using a worm hole. I have to remain optimistic

The spectra are red shifted, but they aren't stretched. Keep in mind that the spectra are a signature of an element. However an element would be changing (expanding) with time so wouldn't it's spectra? The spectra from 15 billion year old objects are not any different than those of today.

Also, the proten electron relationship is NOT a bohr model. By the Heisenburg Uncertainty Principle the electron could be anywhere within certain energy levels. However if the atom was expanding then so would the electron orbits. Lets say it expands so that the radius is 10 times larger. We'd detect that. We'd notice a difference in ionization energy.

I still don't think that density relationships would hold either. Density=Mass/Volume. The mass would remain constant correct? But the volume wouldn't. This would botch the Equation of State which dictates stellar evolution, which dictates how heavy elements form, which dictates how life on this planet could even have been born.

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I can tell this discussion is gonna be an interesting one.

I think you can use this model on a torus shaped universe too... Just a quick thought to come to that conclusion though. I'll have to sleep on it too.

I know the spectra are red-shifted due to the fact that the stars are moving away from us. Nothing I've said would violate that I don't think.

I know an atom is not a Bohr model type thing; I was just using it for simplicity's sake. I don't think midnight is the best time to pull out the 3D wave equation and start dropping in wave functions in expanding 3-space to see if everything holds. Again, a sleeper .

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I think the only way to disprove this is using Energy. Maybe we really should jsut plug this into the 3D Time independent Schrodinger Equation. That hurts my head thinking about though. I can do the particle in a box, but applying it to this?! Ugh... My idea of density is something I still have to think about. The volume would be changing along with the density. The mass can't change though. This is assuming that everything is a spheroid though if not acted upon by an outside force.

Would Quantum Mechanics hold is the question. I'm bothered by the fact that I think it would require more energy to get things done if everything was expanding. Even though relatively nothing would change, if you stepped out of our frame (out of the universe) it would be constantly changing. So although the geometry of the universe is expanding constantly would Energy stay constant? That was a lot of constants constantly. I'm done. This won't make sense when I read it tommorrow.

My desired shape of the universe would be a snake though so that if you were at one end of the snake you could tunnel through space-time to the other side of the snake without crossing the vast distance. That would complicate these ideas quite a bit.

Expanding into? I have no clue. These ideas are way out of human comprehension. It's like the Matrix. Nobody could prove any of that. You have to be able to step out of it to see it.

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Just an add on to that last post. I think this would work still... If you were moving along with the expanding, relativistic object at it's centre, yet were unaffected by the expansion property of the universe, you would see the front edge expanding away from you at velocity v, and see the trailing edge expand away from you at velocity -v, (read: normal to us) but if you were taken out of our universe and into a different frame, you'd see the warped object travelling at whatever velocity it's at. If you were at the centre of this object, and affected by the expansion of the universe, then you'd see nothing unusual.

Argh, brain short... hehe.

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60 mins/secs because the Babylonians used base 60...

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I have to focus on studying. This gets me way off topic. I'll be back later.

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The exams aren't my problem. It's the papers. I have to write a proposal and a termpaper for astronomy and astrophysics. I've never done a proposal and barely understand some of the stuff going on in these ApJ papers. May my professor have mercy on my soul. The termpaper will be easy, but I don't have time and it has to be 15 pages long. Damn them all...

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