h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

"The velocity with which stars orbit the centre of the galaxy can be determined by measuring their 'red shift'. Visible stars are concentrated in the centre of the galaxy. Therefore if the mass of the galaxy was only made up of these stars, we would expect the velocity of stars to fall as we move out into the galactic disk. Further away from a central mass they should not need to move so fast to stay in orbit. But instead they travel at roughly the same speed as stars near the galactic centre."

Have they ever considered that these measurements might simply be wrong?

Yes, they considered that for fifty years before finally accepting that they almost certainly weren't. Stellar velocities can be measured really accurately - article on doppler spectroscopy/red shifts needed.

Today the difficult thing is not trying to prove dark matter, but to disprove it. Many theoretical scientists are trying to do this, in case we can't find any. But it's necessary to think up lots of wild theories to explain everything, it's a lot easier to simply add extra mass to the universe.

It's all very interesting! If there isn't an article on the red shift, I would be tempted to reserch it... My knowledge is somewhat limited on current thinking.

Unfortunatly, astronomers ONLY consider gravity interactions as determining the motions of the observed objects (spiral galaxy, etc.). It is a fact that electromagnetic (EM)forces are MUCH MUCH stronger than gravity. The universe is full of magnetic fields and plasma (charged particles). Even a very small left over EM interaction could easily overpower the gravitational interactions. One rarely sees any mention of these EM effects. Of course, it is very hard to account for EM effects given our lack of local knowledge of the fields in the galaxy in question. To me it makes more sense to try to understand the observed features using KNOWN EM forces than to suppose the exsistence of weakly interacting particles or a new form of matter.

I wrote an article on red shift a few weeks ago. (I hope it covers all your questions.) You can find it at:

http://www.bbc.co.uk/h2g2/guide/U182712

You can talk to Steady-State Richard (http://www.bbc.co.uk/h2g2/guide/U182745) if you want to know more about other theories about the universal red shift.

Hints are welcome if I missed anything.

Steady State Richard is my kind of guy. Nuts to these WIMP theory folks. Thanks for the link. I'm fairly well versed in most of the current nonsense about the BIG BANG (a derisive name coined by Fred Hoyle) that continues to distort our true understanding of the universe. I love the Inflation theory people whose ideas might be described as "and then a miracle happens!". Inflation requires faster than light propagation of (the universe). There is simply no way to account for the large range structure without allowing the universe to ALWAYS EXIST.

Hi

An interesting idea dennishc, but although electromagnetic forces are much stronger than gravity, they can be both attractive and repulsive, so on a large scale they cancel. In order to alter the motion of stars, then some stars would need a small net positive charge, and others would need a net negative charge. It's difficult to see how this could form as charged particles are always formed in pairs and it takes a great deal of energy to seperate them.
Also giving stars a net electrical charge would interfere with (very successful) theories about the nuclear processes inside them. And if most astronomical objects have a net charge, then why should the sun and Earth be neutral. Any electrical forces would interfere with their orbit.

You're written a good article websherpa, I think you should add a few lines to stress that the Universe is expanding about every point, and the observation that galaxies are moving away from the Earth does not mean that the Earth is at the centre of the universe.

And anyone challenging the big bang model, you will need to provide an explanation for the cosmic microwave background (I'm sure you can do it )

MP

Oops!
I'll update that Mammuthus.

Notice the researcher credit?

Right MP, the Earth/Sun seems to be neutral. I was thinking more that the whole solar system is imbeded in a Sun generated Plasma. The plasma is like a conductor. In fact some theories of conduction in wires assume plasma conditions inside the wire. In the Solar system case, this big blob of plasma would be influenced by intergalatic magnetic fields. Motion of a conductor in a magnetic field results in charge polarization. The resulting dipole can interact with other intergalatic fields and the (gentle) resulting forces can easily move the entire system. What do we know of the Solar Wind anyway? Is it electrically neutral? Given the difference in mobility of electrons and protons under the influence of electric or magnet fields I would think neutrality is unlikely - at least in localized regions. I remember years ago that electrical currents in space were not supposed to be possible. Then there was the Van Allen belt discovery! I suspect, that giant currents flow between stars and galaxies. What would these currents do to rearrange the velocities and accelerations of weak old gravity?

The solar wind is a plasma of mainly helium ions and electrons. It is electrically neutral. You're right that plasmas and electromagnetism are important in some areas of astrophysics, but the resulting forces cannot move the entire system. Stars and planets remain electrically neutral and cannot be polarised like plasmas. And the magnitude of these effects in the Milky Way really is very small. The solar wind has a density of a few ions per cubic cm around the earth, it may sway a comets tail, but it can't move a star or planet, let alone account for 90% of the attractive force in the galaxy.

If you're interested in electromagetism and astronomy, research an entry on pulsars or AGNs or something. But it really can't explain dark matter. Really.

Thanks PM but I think that the theory is still in the formative stages. Here is a link that shows star formation governed by magnetic fields.

[url removed by moderator]

There is the continuing problem of how galaxies can GET RID of excess angular momentum so that they can form. Some think that EM forces are strongly involved. I guess I'm one of them. By the way, the solar wind seems to be mostly H ions and electrons with a small amount of He.

MP, I did not realize that URLs were not allowed...sorry. University of Illinois astronomer Richard M. Crutcher has recently concluded that magnetic fields play a large role in STAR FORMATION and the collapse of intersteller clouds. To me, this shows that crackes are begining to appear in the GRAVITy IS ALL THERE IS mind set of the astronomical community. Perhaps we will see the 'discovery' that galaxy rotation has a strong EM component in the near future.

dennis

Let's see some more activity in this coversation. Here is a little exercise in imagination:

Other possible sources for the cosmic microwave backgound radiation:

1) Suppose that the universe is infinite in size and age and the average distribution of stellar material throughout is similar to the amount of stellar material within 5 billion light years of the Milkyway Galaxy. (Steady State Theory?) The Hubble constant then defines the maximum distance or event horizon from which instruments on earth are able to detect electro-magnetic radiation. This is the distance at which the universe appears to be expanding at the speed of light from the viewpoint of an observer on earth. A Hubble constant of 70Km/sec/mega parsec sets this limit at approximately 13.97 billion light years. A constant of 68Km/sec/mega parsec sets a limit of about 14.38 billion light years. The red shifted radiation from all stellar objects approaching this limit is eventually emitted in a range that could be detected on earth as microwaves.

2) Lets turn Big Bang theory on its head and suppose that the cause of the expanding universe is the continuous creation of superstrings whose primary form attribute consists of space with an effective mass that equates to that of the hypothetical dark matter/energy. Space has to move out of the way to make room for new space. This process occurs all over the universe primarily centered around the vast voids (fountains of creation) that have been discovered between the structures known as superclusters of galaxies. This spontaneous creation process also releases photons in the microwave electromagnetic range. This is the cosmic microwave foreground radiation. Each void can be considered to be analogous to an expanding bubble. At the borders between bubbles exists compression zones where baryonic matter is created when the energy of space/dark matter/dark energy is compressed into the equivalent volume required for baryonic particles. Then, in a process that occurs over billions of years, enough baryonic matter is created in the compression zones to start the formation stars and galaxies. Instead of all the energy and mass in the universe being created in a singular mega-catastrophic event, creation of the universe is a continuous eternal process.

I must confess of admiring several of the articles in this section.
Conceptually,if one is determined to make out a case for EM forces as a direct cause of DARK MATTER in lieu of exotic particles particularly,then one could argue the nature of so called ' DEAD MAGNETARS '. Some reckon one destroyed the dinasaurs after a savage 'flare-up'and still might finish life off on this planet. However,the DARK MATTER subject holds sway here,not what a 'live one'does for local astronomy. So if EM is to remain a source of imaginative reasoning,the other legal-corner has to be agreed upon. What one cannot see one cannot reject. What is a 'dead magnetar?' A 'dead leaf' falls off a tree;it is not so dead biologically and hence not dead bioelectrically either;(Japanese sc.are good at this subject). Why not assume that ' dead magnetars ' are strongly capable of EM contributions to the Dark Matter Controversy while doubts remain?.

A route to overthrow D.M. - if it exists at all - requires an examination of any chances of misconceptions about the nature of inertial connectivity. How about this for a tilt at the traditional quintain. I am not so sure I don't fall off the horse;what do you think?
Drag forces of stars,planets,act upon the spacetime metric to warp it under Einsteinian Relativity. ie The General Relativity. A costly enterprise is earth-satellite story in our own system. Gen. Rel 'trophy' to-be is of Italian origin. Although very small,each planet is inertially separate to drag orbitally,according to its position with respect to a circular orbit; I can show that it's party with a calculation involving the Roche of the planetary object. Take my word for it for the sake of the overall argument meanwhile.These men do know why they have to prove it. Now suppose the galaxy replaces ones interest in the local challenge. Could one imaginatively set-up a circle of macroclassical standing for the purposes of outlining the
relative orbital drags of the stars travelling round the centre? Its no more obvious. The same type of analysis would apply,but many stars are the casebook. It seems a collosal imputence to say it has anything
to do with the Dark Matter mystery,but wait a mo. I postulate and explain thus;-
The type of inertial operation ident.with CELESTIAL drag-forces would
set itself at odds with the usual idea of considering the outer systems of masses connected to the central operations for the velocity
arguments. Analytically,this underlying theory depends on where the circle is deemed to be situated . As party with any sigma amounting to radial equivalence for critical stability of the whole galaxy. The idea
being to accept that an 'inner system of masses'and an 'outer system'of rotating stars in relation to such a circle (like Venus orbit in ours)is the total of all the individual stella operations. What makes this kind of argument difficult has to be a lack of familiarity with the
method associated with calculating the Einsteinian 'Drag Force' on an orbit. There is inertial dependance upon an enormous
quantity of stars regionally inner and outer,employing comparatively short and long distance from any such 'circle', The centre of the galaxy isn't really the issue,if the nature of a reaction - to 'Drag
Force'warping of spacetime metric - infers a partial separation of the frames. The circular reference conditions it as it does the case for planets in our smaller system. Difficult I agree,particularly as Einstein's Gen Rel. has yet to be established by the Italian-USA project. Whether one can make a priority of the subject for a D.M. tenuous link does depend on
whether one can reasonably parallel the velocity paradox of the galaxy with our own system. The Einsteinian Earth-drag p.a will eventually cause a refocussing of gravitational operations simply because the orbit is slightly-ever so-unstable. Thus it gets out of phase on
historical scales. Also in Jovian regions, asteroids 'jump' and velocities change
incrementally on principle of the 'drag force'becoming a source of eccentricity changes. The relationship between star and planet gets
out of phase timewise. (Its a modern problem for astronomical
timekeeping at the moment of our history). Its a celestial dynamic. Hence in a large galaxy,if one borrowed the idea to assume that it
works to create a differential warping of the spacetime ('taken about a circular reference' within it imaginatively ), why should it not work
like a mirror with respect to the innermost and outermost velocities?
In our own planetary system the truth is cunning.(Der Herr Gott). The escape velocity of Mercury happens to be approx. the same sort of value as the rotational velocity of the outermost Pluto. Neither property are
related in the normal way. It is a 'coincidence'. But Time could be a coincidence made up of complex transitional operations anyway. The most learned PROF S HAWKINGS said so in his book about Time last century. In other words if spacetime itself is on the move under more extreme conditions -our galactic D.M.mystery being the implication here -it creates a pressure difference to balance its books. Velocity paradox would be a certainty although the galactic case would seem to work inversely.Is it not the same truth,about a 'mirror effect'one sees in the galaxy with the outermost stars travelling faster along their orbit than dynamically required under ordinary logic rules. An escape-pressure. So given the planetary paradox of the inner escape vel.of Mercury;the outermost orbital velocity,there is this inference of a spacetime creating pressures to balance its books.
So the Theory of Spacetime Drag-Forces summated is a Theory of The Kinematic Metric. At the end of these conversations it appears to run parallel with the D.M concept but independant of any need for a
dimension for an associated Mass in the Dark. Space works like that.Doubtless science will opt for representatives of both scales in spite of this concept being an extension to the usual
descriptive reasoning. If this is a quantum-gravity theory,it involves the General Relativity at a most acute stage of its history.