Just a few more posts....

Think I will be able to complete the basics of Dark Matter...then will move on to Dark Energy!

What might the dark matter be?

There has been quite a lot of speculation about what dark matter really is. Or what is constitutes of.

We know that dark matter can be anything that is non-luminous. Such as planets. The earth is not particularly massive, but planets like Jupiter are rather big. Still there is a problem. First, we assume that planets only form around stars. And if that is true, then even the biggest planets are dwarfed by stars near them. That means, they contribute only a few percent of their mass. Another Omega = 0.005 or so, which clearly isn’t enough.

A bigger problem comes from the Big Bang Nucleosynthesis (BBN). At the birth of the universe – as we understand it at this time – when the big bang occurred, the universe was an extremely hot soup of all sorts of particles. And then it grew and got colder and the ‘ordinary matter’ particles such as Neutrons, Protons and Electrons started to cool enough to form atoms of the material in the universe as we see them today. This is predominantly Hydrogen and Helium.

BBN is a great story. It not only conveys that Hydrogen and Helium are by far the most abundant elements in the universe, but also gets them quite accurately in terms of their proportions. But, there is a catch.

The amounts of each element that forms, depends very much on the amount of ordinary atom-forming matter; what are known as Baryons. BBN predicts all the right amount for the current universe only if the original amount of baryonic matter was about Omega=0.1

The amount of baryonic matter is larger than the amount of visible matter, hence there is some dark ordinary matter, like planets and burned out stars. But there is not enough to explain rotation curves and cluster velocities.

Dim Stars – Jupiter, Brown Dwarfs, White Dwarfs

Other ‘ordinary matter’ candidates include stars that are not that massive enough to start burning and become luminous. These are called ‘Brown Dwarfs’, or even Jupiter. If Jupiter was ten times heavier, it would have started burning as a small star. These possibilities suffer the same problem from BBN as planets. There just isn’t enough baryons to make a difference.

But it is always possible that BBN is wrong. And there are many looking into that too. Still its success has been rather high and people would rather concentrate on other possible solutions.

Exotic Matter

Even though the term exotic is used, Exotic matter does not have to be exotic at all. It is just matter that isn’t electrons, protons or neutrons. Lots of particles other then these are known to exist. And some theories do use them to solve the dark matter problem.

Neutrinos

Neutrinos are particles that are known to exist. They are thought to be massless, but there have been some recent evidence that they may have a small mass. There are so many neutrinos in the universe. That even a small mass would be important for dark matter, a mass of 93eV, or one five-thousandth the mass of an electron, would make Omega=1

WIMPS

Most other exotic matter falls into the category of WIMPS, or Weakly, Interacting Massive Particles. These are, as a class, heavy particles that only interact weakly with other matter. There are many possible such particles. They do have some exotic names, such as, neutralinos, axions and the like.

Changes to Gravity

One possibility – might seem quite far fetched – is that we don’t really understand gravity particularly well. We only know of gravity and its laws on individual objects and its effects on other object. What we do not know is if gravity can collectively act as a single force. Or even how gravity works on large size galaxies. This seems odd, but must not be discounted.

How much Dark Matter

Cosmologists like to talk about the amount of matter in the universe. This is expressed in a term known as Omega. It is quite simple to understand. Omega is defined so that a closed universe or a universe that is massive enough to eventually collapse back onto itself is said to have an Omega larger that 1. And an open universe or one that expands outward forever and will never collapse onto itself is said to have an Omega of less than 1. Something in between these two known as a ‘flat’ universe, one that perfectly balances between the two has an Omega=1.

The amount of visible matter in the universe is about Omega=0.05. Not very much there at all. Physicist like to believe that for the universe, the total of all of the mass is Omega=1. This would mean that dark matter makes up the other Omega=0.95. Or, 95% of the universe would be dark matter! More realistically, there isn’t too much evidence for Omega being larger than about 0.4. This would make the amount of dark matter be Omega=0.35. And that means that 88% of our universe is complete mystery.

Rotation Curves

There is however some stronger evidence and ways to find out. Simply, because they provide mote reliable data and could be done for a larger number of galaxies. This happened in the 1970’s when people started measuring what is known as rotation curves for galaxies.

It is a known fact that galaxies spin around their centre. Like the planets orbiting the Sun. Just like planets orbiting the Sun, they too follow Kepler’s Law for orbits around the centre. Kepler’s Laws state that the rotational velocity around the centre depends only on the distance to the centre, and the total mass that is contained within the orbit.

Therefore, by finding the rotation velocities along a galaxy, one can ‘weigh’ the mass of the galaxy inside that orbit. The rotation speeds have been found to be very high and above what is expected. This indicates that there is a great deal of mass in the galaxy that we cannot see. This seems to be the case for many spiral galaxies, just like our own one. The same results keep coming up. Here is the strongest evidence that dark matter exists, as something that we cannot see is causing the mass.

Cluster of Galaxies

The first evidence that there was a decent amount of significant matter that we could not see was in clusters of galaxies. These are simply aggregates of a few hundred to a few thousand clusters otherwise isolated in space.

In the 1930’s two relatively close clusters were examined. The Coma cluster and the Virgo cluster. Since clusters are made up of individual galaxies, they looked into each cluster. What they found was that the velocities of the galaxies were very different to what they expected. What did this mean?

Before answering that, we must understand that in a group of galaxies the only important force is gravitation. It is the pulling of the galaxies on each other that gives rise to their velocities. The velocities can indicate the total mass inside the cluster in two ways. The first way is rather simple: The more collective mass inside the cluster, the greater the forces acting on each galaxy. Which in turn accelerates the galaxies to higher velocities.

The velocities can indicate the total mass inside the cluster in two ways. The first way is simple; the more mass in the cluster, the greater the forces acting on each galaxy, which accelerates the galaxies to higher velocities.

The second way that velocities indicate the mass in the cluster is also rather simple. If the velocity of a given galaxy is too large, it will be able to break free of the gravitational pull of the cluster. Just like in a escape velocity. That is if the galaxy velocities are larger than the escape velocity of the cluster. This means the galaxy will simply leave the cluster. Hence, by knowing that all galaxies have velocities less than the escape velocity, one can estimate the total mass.

Looking back this was fairly strong evidence; still it was not treated as such. The also lies a problem here. When doing observations such as this, there are many ways these can go wrong; Contamination’.

When we are observing something as vast as a cluster of galaxies, even though the velocities are quite large, they are negligible when compared to the vastness of the cluster it lies within. For that matter, even observing a cluster over years, does not show any significant change. One cannot really see them running around. Hence, it can mean that a galaxy with a high speed is leaving the cluster, or may have never been part of that cluster, or maybe just passing through, or maybe it was only a galaxy in the foreground ; in front of the cluster, along the line of sight to us. If it is any of these the velocity data will be misleading.

Non Luminous Matter

Just like in any other science, there are two ways to detect an object. One is by observing it directly, and the other is by observing the effects that it has on another or more easily observable objects.

We all know that there is a lot of matter in the night sky that we cannot directly see. When instruments such as, telescopes, or even radio telescopes, are used, one can only see objects which emit light or radio waves. Not everything in the universe does this. Just like our earth. We wouldn't be able to see planets like our own, because they would be too dim to see.

If one was to add up all the mass of all the planets in our solar system, it would be significantly less than one percent of the Sun's mass. As a result of this- non-luminous matter - it never caused great concern. At least for the time being.

Cosmology today

Cosmology is the study of the beginnings, formation, and evolution of our Universe. In today’s context it is in a badly confused state. Right now, we have no idea as to what makes up 99% of the Universe. This, needless to say, is very embarrassing. Although much of what is visible (physical matter) in the Universe is becoming comprehensible, with great recent strides in understanding star formation, galactic structure, and spectacular events such as supernovae, it would appear that there is another component of the universe - possibly making up most of its mass - which we cannot see, and we do not understand; DARK MATTER.

This subject has been around for sometime. Lots of speculations and references. So much so that it has found its ways into the a crappy X-Files episode. We need to find the real answer to this dilemma. Or do we have to wait for another Einstein to come along?

What is it really? How do we know of its existence? And how do we know it is really ‘dark’? In the coming days, I do not have answers, but will try to come up with some thing that will be within the boundaries of physics and its laws as we know it at present. Please feel free to comment.

Dark Energy

Dark energy, a mysterious force that no one understands, is causing the universe to fly apart faster and faster. Only a few years ago, if you'd suggested something like that to astronomers, they would have told you to spend less time in front of the TV and more time in the "real" world.

But dark energy is real ¾ or at least, a growing number of astronomers think it is. No one, however, can truly explain understand it, but seem to know the effects of it. Kind of, got everyone one in a bit of a twist.

Dark energy entered the astronomical scene in 1998, after two groups of astronomers made a survey of exploding stars, or supernovas, in a number of distant galaxies. These researchers found that the supernovas were dimmer than they should have been, and that meant they were farther away than they should have been. The only way for that to happen, the astronomers realized, was if the expansion of the universe had sped up at some time in the past. Until then, astronomers had generally believed that the cosmic expansion was gradually slowing down, due to the gravitational tugs that individual galaxies exert on one another. But the supernova results implied that some mysterious force was acting against the pull of gravity, causing galaxies to fly away from each other at ever greater speeds.

At first, there were a lot of questions; perhaps the supernovas were dimmer because their light was being blocked by clouds of interstellar dust. Or maybe the supernovas themselves were intrinsically dimmer than scientists thought. But with careful checking, and more data, those explanations have largely been put aside, and the dark energy hypothesis has held up.

In one sense, the idea is not completely new. Einstein had included such an "anti-gravity" effect in his theory of general relativity, in his so-called cosmological constant. But Einstein himself, and later many other astronomers, came to regard this as a kind of mathematical contrivance that had little relationship to the real universe. By the 1990s no one expected that the effect would turn out to be real.

Anti-gravity may not be the right way to explain dark energy. It is not an opposite of gravity. It’s character is just as General Relativity explained it, if it had negative pressure.

If you think in terms of the universe as a very large balloon,when the balloon expands, that makes the local density of the [dark energy] smaller, and so the balloon expands some more …. because it exerts negative pressure. While it’s inside the balloon it’s trying to pull the balloon back together again, and the lower the density of it there is, the less it can pull back, and the more it expands. This is what happens in the expanding universe.

The supernova evidence suggests that the acceleration kicked in about 5 billion years ago. At that time, galaxies were far enough apart that their gravity (which weakens with distance) was overwhelmed by the relatively gentle but constant repulsive force of dark energy. Since then, dark energy's continuing push has been causing the cosmic expansion to speed up, and it seems likely now that this expansion will continue indefinitely.

It means that if you look out at the universe today, and if we wait many billions of years, everything will be flying away faster and faster, and eventually we’ll be left quite alone. As we will be so far a part from each other and the influence of another object will be nearly negligible.

Aside from such grim forecasts, dark energy is causing quite a bit of upset for astronomers who have to adjust to an unexpected and outlandish new view of the universe. Already, they have had to accept the notion of which is now thought to far outnumber ordinary matter in the universe, but which has never been detected in any laboratory. Now, the arrival of an unknown force that rules cosmic expansion has added insult to injury.

As for dark matter itself, it is quite hard to explain, Nobody’s really sure, and then dark energy makes us even more unsure. All that can be said is that the 90% - 95% of the universe is made up of two ingredients that nobody really understands. All we know is the little of physical matter. Seems like we have not moved that far, have we?

Quantum mechanics took us two generations of people to understand it comfortably. Quantum Mechanics, General Relativity and lots of other things cannot be worked out in a laboratory. The same applies to dark energy.

The only comfort dark energy provides us now, that it to some extent explains the expanding universe.

Unintelligence

Some one asked me a question, thought it is best to answer this and post it here.

 Question: 
Assuming the earth surface area as 1, then the total for all the planets and moons is not
more than 1000. So the total energy of the sun falling on all these worlds is no ore than
two millionths. This shows unintelligent design. Why waste millions of times of more energy
trying to heat up empty space? Its worse since most planets radiate more energy to space
than they receive from the Sun! Where does all the energy go in the end? If space was not
expanding would the energy from all the suns interact and heat up interstellar matter and
hurt it at us?

Answer: 
It is not unintelligent design; it is about the universe obeying the laws of physics/nature
in its entirety. These are the laws that govern everything. From the stars to the
microscopic particles.

Interestingly you have called it unintelligent design that means you do accept the fact
that there was a creator behind all this.  You also need to realize that if things are not
the way they are, you would not be here to ask this question!!!  The perfection in
the design is that the least amount  of work is being done. You could say the universe
likes to do the least amount of work. If you recall, we have all learnt in our early
Physics lessons that  the most efficient systems are those that deliver with the least
 amount of work. In that sense, the universe, our solar system, the earth is set up
in the most efficient way.

If this design bothers you so much, it means you are just a confused individual.
It might be better if you came up with some intelligent questions in your mind,
than to look at the 'unintelligence' of an efficient system.

The JW's

Had this interesting conversation today with some friends. One a JW, the other a confused
Christian. The JW was insisting that JC was none other than Michael the Arch Angel.
The confused man was saying things that eventually made him more confused, and I was
insisting that JC was not M the Arch but he was God himself. God in the form of man at that
time. And his fundamental purpose was to come down and show us all how we should live.
Wonder if there is anyone who emulates his lifestyle. From there  it was a talk on pre-destiny.
I think we are all predestined to take a path that had been plotted out before we came into
being.That also means that I can do nothing to change my fate. It is God in the driving seat
and he decides where the ride of life takes me.

As I see it, this world has 2 kinds of people. You have the inherently bad people and the
inherently good people. And that does not mean anything. Cause bad people will do good things
and good people will do bad things. Whatever they are, we will always see the inborn quality
of these people if we were to look closely. Just that we do not have much of a choice in this,
and we all have a role to play. The question is, what am I?
Have to try and work that out.

All about Blackholes

An object that sits in space minding its own business. A black hole is an object inspace from which the escape velocity is equal to the speed of light. Since the speed of light is the fastest we know, it also means that nothing can travel fast enough to excape from inside a black hole. Simple as that. What is escape velocity??? Every object in space has an escape velocity. It is the velocity you will need to get out of its gravitational influenze. A simple formulae is

Escape Velocity = (2GM/R)1/2

were, G= Gravitaional Force, M is the mass of the body, and R is the radius of the body....why not try working
the escape velocity of the earth, then?