Introducing "Dark Matter"

[Nabobalis]

I suggest you focus on the dark matter and skip the argument about the size, shape of electron. There is no point to defend a mistake.

What mistake?

 

[Doveaman]

We see the effects of mass on those rotation curves.

No we don't.

Rotation curves are unlike what we would see if the observed mass was the cause.

What you see are effects of unknown cause. You then assume they are gravitational effects, and then you assume there is missing mass causing the assumed effects.

Unless you have found the amount of mass necessary to produce such effects, you cannot claim we are seeing the effects of mass. That's a blind assumption, and that's why you are now groping in the dark.

 

[Nabobalis]

It has a radius?
What exactly is a point? And does a point have a radius?

It is likely to have a radius, the question is what will it be? So far it is so small to be unmeasurable, we treat them as point like particles. Further, the standard model models all elementary particles as point like and so far it hasn't been a problem.

 

[Doveaman]

It is likely to have a radius.

Does this mean it is likely to be round or circular?

 

[Nabobalis]

No we don't.

Rotation curves are unlike what we would see if the observed mass was the cause.

What you see are effects of unknown cause. You then assume they are gravitational effects, and then you assume there is missing mass causing the assumed effects.

Unless you have found the amount mass necessary to produce such effects, you cannot claim we are seeing the effects of mass. That's a blind assumption, and that's why you are now groping in the dark.

We have the rotation curves, those curves are directly related to the mass of the galaxy. What we see is mass of the galaxy not decrease as we go further out to the disc. There seems to be missing matter.

 

[Nabobalis]

Does this mean it is likely to be round or circular?

If it does have a radius, it could be anything. Will have to see in the future.

 

[dbcsf]

We have the rotation curves, those curves are directly related to the mass of the galaxy. What we see is mass of the galaxy not decrease as we go further out to the disc. There seems to be missing matter.

I am not a scientist, but from what I have learned I agree.

I do not believe anyone is saying they know anything for certain. The way science is done is that scientists observe phenomena and develop a hypothesis as to what is causing the phenomena.

Next scientists try to gather data from experimentation and observation to support their hypothesis.

Currently the dark matter hypotheses is not well supported. I believe everyone agrees with that. We can experiment with gravity. Based on what we know of gravity scientists believe the best possible hypothesis for explanation of the observed rotation of the galaxy is dark matter.

I haven't heard anyone say the dark matter hypothesis had collected enough support to be proven or anything. It is just the current best guess based on the science we currently know.

From what I have heard no other hypotheses have come forth which can model the galactic motion we observe.

Consequently, I don't think the next step is to through out the dark matter hypotheses. We are still in the "looking for the mass, or the alternative hypothesis" stage.
We either need to find the missing mass or come up with a new hypothesis which is more credible than the dark matter hypotheses.

So what is dark matter?

1) It has mass
2) It is not visible
3) It is in a quantity sufficient to explain the galactic motion we observe
4) It is a theoretical mass, as we have not found it yet.

 

[juvenissun]

It is likely to have a radius, the question is what will it be? So far it is so small to be unmeasurable, we treat them as point like particles. Further, the standard model models all elementary particles as point like and so far it hasn't been a problem.

Here is your mistake. Admit it and move on.

 

[NGC 6712]

It is likely to have a radius, the question is what will it be? So far it is so small to be unmeasurable, we treat them as point like particles. Further, the standard model models all elementary particles as point like and so far it hasn't been a problem.

Actually it is not likely to have a radius. It is very likely to be a point.

 

[Nabobalis]

Here is your mistake. Admit it and move on.

How is that a mistake? NGC 6712 has corrected me, they are point-like and have no radius. So I don't see your issue.

 

[Nabobalis]

Actually it is not likely to have a radius. It is very likely to be a point.

Interesting. I know that QFT treats them as point-like. But I thought that some people thought it should have some radius(larger than the plank length)?

 

[juvenissun]

How is that a mistake? NGC 6712 has corrected me, they are point-like and have no radius. So I don't see your issue.

Point is an idea. Particle is a substance. I have a point in me where is the center of my mass. But my body has a size.

I am curious on what NGC 6712 said too.

 

[Nabobalis]

Point is an idea. Particle is a substance. I have a point in me where is the center of my mass. But my body has a size.

I am curious on what NGC 6712 said too.

Points don't have a radius. Elementary particles don't have a radius and as such are points. It has nothing do with calling them dark.

 

[neutralino7]

.

 

[Doveaman]

I do not believe anyone is saying they know anything for certain.

They are saying we are observing gravitational effects. That sounds pretty certain to me.

The way science is done is that scientists observe phenomena and develop a hypothesis as to what is causing the phenomena.

I agree. But we cannot say we are observing gravitational effects if we are not observing the mass necessary to generate those effects. The phenomena we are observing here is rotation curves, nothing more.

Next scientists try to gather data from experimentation and observation to support their hypothesis.

Then gravitational effects would be the hypothesis, and now we are trying to gather data (dark matter) to support this hypothesis.

Currently the dark matter hypotheses is not well supported.

Therefore gravitational effects are not well supported.

I believe everyone agrees with that. We can experiment with gravity. Based on what we know of gravity scientists believe the best possible hypothesis for explanation of the observed rotation of the galaxy is dark matter.

So then you agree that gravitational effects are only a hypothesis that is yet to be verified with the discovery of dark matter, right?

I haven't heard anyone say the dark matter hypothesis had collected enough support to be proven or anything. It is just the current best guess based on the science we currently know.

Well then we should treat gravitational effects as an unconfirmed hypothesis and not as an observed fact. But people keep telling me we are observing gravitational effects as if this is an observed fact. The only thing we are observing here is rotation curves, nothing more.

From what I have heard no other hypotheses have come forth which can model the galactic motion we observe.

That depends on who you are listening to. I've heard of at least one other.

Consequently, I don't think the next step is to through out the dark matter hypotheses. We are still in the "looking for the mass, or the alternative hypothesis" stage.

So you keep it because it’s the only thing you have. Fair enough.

We either need to find the missing mass or come up with a new hypothesis which is more credible than the dark matter hypotheses.

So if we don’t come up with a new hypothesis in this century, we just spend the next century looking for missing mass, right?

So what is dark matter?

A huge gap in scientific knowledge.

1) It has mass

How do you know that?

2) It is not visible

How do you know that?

3) It is in a quantity sufficient to explain the galactic motion we observe

How do you know that?

4) It is a theoretical mass, as we have not found it yet.

If it's theoretical, then your list above is meaningless.

Theoretical:

1. of or based on theory
2. lacking practical application or actual existence; hypothetical
3. Given to theorizing; speculative
4. using or dealing in theory; impractical

 

[Michael]

A point is technically a squeezing limit. It is the dot (circle for 2D, sphere for 3D) that excludes everything except where the point is defined. In other words, if the point is at x=3 in 1 dimension, the radius of the point is half of the diameter of the location x=3 on the number line, excluding the infinite amount of numbers to the left and right of x=3. For this reason, a point has a radius of infinitesimal, not zero.

That's my understanding as well, otherwise the density is infinite, and every particle becomes a "black hole".

 

[Michael]

Dark matter is dark not because of its color, but because it does not interact with electromagnetic radiation.

FYI, I cited two specific examples earlier in this thread where "dark matter" (unidentified/missing mass) turned out to be ORDINARY STARS! IMO it is WAY too early to be claiming ANYTHING about the nature of "dark matter/missing mass". All we REALLY know is that we can't account for all of the mass in a given galaxy based on our current modeling techniques. The rest is pure speculation.

 

[Michael]

Points don't have a radius. Elementary particles don't have a radius and as such are points.

While I agree with your first statement in terms of pure mathematics, your second statement is false and demonstrably false as that laser image of an electron demonstrates. They particle itself reflects photons in a particular and specific way, based upon the particle's size, it's SHAPE and it's energy state. No subatomic particle composed of mass can achieve a ZERO radius, otherwise it must also achieve an INFINITE density. That's not the way it works as that photon scattering pattern from an electron demonstrates.

 

[Nabobalis]

All we REALLY know is that we can't account for all of the mass in a given galaxy based on our current modeling techniques. The rest is pure speculation.

That is the point. Current models can't account for what appears to be extra mass in galaxies. Cosmoglsts came up with dark matter and we will see how it goes in the future. You don't like it and want an EU. Time will tell how it goes.

 

[Nabobalis]

While I agree with your first statement in terms of pure mathematics, your second statement is false and demonstrably false as that laser image of an electron demonstrates. They particle itself reflects photons in a particular way, based upon it's size, it's SHAPE and it's energy state. No subatomic particle composed of mass can achieve a ZERO radius, otherwise it must also achieve an INFINITE density. That's not the way it works as that photon scattering pattern demonstrates.

Well I was sloppy with my words. The radius should be infinitesimal.

But those images are of the charge distribution of the electron. That is how we see electrons, its charge.