Forming of the universe structure Zeng YaoHuan >>Popular science article
Universe one can't control and repeatable experiment body, this is astronomer's heaviest putting on the door, nobody can make one the sun inside the laboratory, nobody can control the growth of the sun inside the laboratory too, just like mouse in the biology laboratory.
Targets who the astronomical physicist studies are all controlling and not repeatable experiments, this does not represent astronomical physics either a science, science has a characteristic or predictability, a good theory has better prediction, the astronomical physicist can predict some nature's mysteries.
Universe great yardstick structure
　　Astronomy can't be controlled and the not repeatable reason lie in the yardstick of the time and space, only a volume of the sun has 1,330,000 times of the earth, life-span of the sun say and have billions of years little, this far exceeded the imagination of common people.
It is the moon smaller than the earth in volume, even if can make one the moon at the earth, we can't duplicate environment of the moon either. It is transient that it is the comet to knock into Jupiter, it is too because from space yardstick too the far,can't have.
Existence of the sub star in but the astronomical physicist can predict through rigorous science, can predict the existence of the black hole too, even predict the present temperature of universe has absolute temperature 3K only.
Astronomy is a science definitely!
　　Cosmology time and issue, space of yardstick that house run into far more than other, not only the target observing it is unable to control, but also can only observe once, because we have only a piece of universe.
Even can only observe once, can't look carefully either, is limited to velocity of light and limited life-span of universe, the universe of our real observation is only a part. Though cosmology is limited to the deficiency of the materials, let the theory study the family in larger imagination space either, it is some most basic problems to set up one's own universe models, for example size, age and composition, universe of material of universe of universe at target that study still.
　　The awkward situation in improve recently, observe the progress of technology and instrument, can let the astronomer get the materials of different wave bands, the joining calculated in simulation, let some cosmology theories be verified too, and compare each other with observing the materials.
For example before Kazakhstan cypress space the telescope and universe background survey materials not latest that ship offer of, and the big thunderbolt model is identical each other, the materials that the recent Boomerang balloon observes assert further the universe is smooth. In numerical simulation, because the progressing fast of computer with high capacity and efficiency, make use of the parallel computer of huge quantity made up of thousands of processors (Massive Parallel machines) Can carry on more careful calculation to various kinds of phenomena and various kinds of models in the universe, the simulation achievement introduced here is a reason of forming about universe great yardstick structure.
　　Family once thought cosmology under great yardstick, it is very even that the material is distributed, galaxies which is similar to the Galaxy are all dispersing in the universe each corner evenly.
From observation for decades find recently, in light-year of range memories is it similar to structure, foam of form to have, most galaxies are gathering into a group, call that the cluster of galaxies, there are thin slices between the clusters of galaxies (sheet) With the filament (filament) Link to each other, these thin slices and thin structure like silk are formed by galaxy institute, is the cavity extremely low in density around thin slice and filament (void) ,These cavities nearly take the form of ball, the diameter is probably several 1% of the size of universe.
Can see great above-mentioned yardstick structure from Fig. Dr.eye: 1, the snack in the picture represents galaxies, the size of galaxy in the middle nearly has 10kpc (1kpc about 3300 light-years) ,There is the size of the cluster of galaxies from 1Mpc to 10Mpc (1Mpc equals 1000kpc) ,Thin slice or large cavity that filament surround have 30Mpc size to reach 50Mpc, the size of universe of now exceeds 10000Mpc.
For explain the universe old yardstick forming of structure, cosmology house propose some theory is it can agree with materials observed to hope.
　　Suppose most materials appear with the splendid fixed star type attitude in the universe, gravitation is to assemble into the main effort of different all kinds of structures by these materials.
Up till now, this kind of idea is suitable for our solar system, but in bigger yardstick galaxy, the structure of or the above, does not seem affective, according to motive force behavior of a spiral galaxy, over 90% of the materials are invisible in the galaxy, do not exist in the fixed star.
It is more important, light to can not form universe old yardstick structure by material that will give out light these, unless the material that the universe includes is far greater than giving out light the material (fixed star) ,The astronomer calls these materials not giving out light the dark material (dark matter) .
According to law of universal gravitation of now, seem universe give out light quality of material too little, (density is disturbed a little) from material that universe just begin being even slightly Can not form the great yardstick structure, need more time to form the great yardstick structure in other words.
The dark material of cold and hot dark material
　What thing is the dark material which occupies the most quality of universe?
The astronomer has a lot of conjectures to the composition of the dark material,
some astronomers think the dark material is actually the general normal material too, only because a certain reason is unable to give out light, but formate the theory to calculate from the universe and light material, can give and draw up a upper limit for the general material in the universe, but this upper limit is still unable to form the great yardstick structure in universe and existing age.
The previous astronomer thinks the little neutron may be a backbone of the dark material, find the quality of the little neutron is very small, but the quantity of the little neutron is very heavy from unifying the theory greatly, total quality is enough to take on the important task.
Because the quality of the little neutron is very small, its speed of movement is close to the velocity of light, as very fast as sports of the hot air and molecule, an astronomer also calls little neutron the hot darkness material (hot dark matter, HDM) .
These dark materials that come out more can help the gravitation of the general material to shrink, let primitive density is it shrink gradually to disturb a little, form galaxy and cluster of galaxies, hot dark sport of material speed too old, it was unable to shrink that the galaxy size density were disturbed a little, it was the cluster of galaxies that formed at first, then split pieces of galaxy into another, so hot dark material model call pancake model also (pancake) ,But the newest observation finds
Comparatively popular model is called the cold dark material model (cold dark matter model, CDM) now ,The backbone of the dark material of cold must have fainter reciprocation with general material, quality is larger too, the movement is much slower than the velocity of light in speed, so it is cold to call it, find according to computer numerical simulation cold dark material can make universe initial density disturb long to become great yardstick structure a little.
　　The only adjustable parameter in the cold dark material model is the size that is disturbed of the initial density of universe a little, the information disturbed a little about the initial density carves seal in universe background radiation, universe background radiation whether one full of in whole photon of universe, photon this present temperature only absolute temperature 3K probably (0 degrees Centigrade is equal to absolute temperature 273K) .
When the big thunderbolt just happened, photon in the universe and material temperature are very high, very dense, collide to have a good chance between the two, as the universe expands, the temperature of the two drops gradually, about 10,000 years in the universe and age, after the material and photon no longer collide each other, the two part company with each other each, and previous material distribute information is it on the distribution of the photon, keep till now straight to brand too.
　　The initial density of universe branded on the photon is disturbed and can get through observing a little, survey the ship in universe background (COBE) The most famous achievement is that quantity is examined to 2.73K background radiation, this is a boldface radiation, COBE amount result that comes out is as the same as the textbook, this is a great achievement of a theory.
Another information that relevant density disturb a little is the change situation of the space, COBE measures out the change of background radiation temperature in 1 billion light-years of yardstick, changing amount is only 1/100,000.
The numerical simulation can follow the trail of the gravitation change situations of more than 17 million drops of particle continuously, the high analytic degree of density changes that can tell six orders of magnitude s of more than 17 million drops of particle, watch one have a million image that color change just, high simulation to analyze degree result enough observing and comparing each other so.
Besides changing in density, it nearly has kpc that the space of the numerical simulation is analyzed degree, can tell galaxies clearly, and the size of thin slice and filament structure that the galaxy form nearly has 10Mpc, analyze degree 10,000 times bigger than the space, just like take ten centimeters of distances between one kilometer of ruler measurement in such analytic degree.
　There is only reciprocation of gravitation between the particle in simulation, all particle is in a piece of space expanding constantly, it is from z to usually imitate =100 begins, z, on behalf of moving red, according to Kazakhstan's cypress law, the celestial body the farther from us, the larger the speed far away from we is, the bigger the red moving amount is. nd the celestial body the farther from us, representative the more early universe, so astronomer daily to move z time, representative of universe while being red, and z =0 express and has not moved red, it is now.
　　The age of the real universe exceeds z =1000, is far greater than initial (z of simulation =100),Slightly understand simulated person may think number value: Why not begin simulation when the universe is the earliest?
The main difficulty lies in the question on technology, should be from z =1000 simulation beginning needs to take too much calculation time.
Very luckily, from z =1000 gets to z =This period of time of 100, the whole universe evolves the course and returns the on-line state of place, can to be simple calculate with the theory, the density needed disturbs the frequency spectrum (that the density disturb the distribution state in the space a little) a little at the beginning of calculating in simulation ,Can calculate from the theory, can be formated from observing again (recombination) Disturbing frequency spectrum a little of the time is in the cold model of dark material and flat universe, it disturbs to be linear to increase a little, can calculate out simulation initial a little disturbing so.
　　There is frequency spectrum disturbed a little, simulation distribute the particle in space according to frequency spectrum when being at the beginning, usually place the particle on the regular network lattice point to have.
In order to assuare that there is characteristic that universe expands, each particle will give definitely an initial speed according to Kazakhstan's cypress law, each particle has position and speed, can let the simulation procedure begin to carry out. The second Fig. is the course that the universe great yardstick structure is formed, the third Fig. is the last result of simulation, probably there are several hundred pieces of particle in each bulk thing of caking in these pictures, total quality is probably that a galaxy faints. Is it choose after coming out to faint galaxy of whole pieces of picture, can analyse power characteristic that galaxy faint further, for example galaxy faint rotation, collapse to contract (collapse) With amalgamating (merge) .
Usually imitate and can find about 10,000 of galaxies and faint in the last result, the quantity is enough to do some statistical analysis, for example the moving each other while fainting of galaxy and space distribution within the range of 10Mpc.
Size and space distribution that the galaxy of simulation faints and observing the difference not too great of the result, in addition it calculate galaxy faint particle in revolve round the sun speed, astronomer is it find fixed star of galaxy revolve round the sun speed to divine way to rein in law according to gram to observe, planet in solar system revolve speed it distributes to be to divine law of reining in according to gram, fixed star examined to surround and watch revolve round the sun speed convergence a definite value outside galaxy, this agrees with result of simulation
Galaxy that simulation come out faint quality it distributes to be to increase as the distance increases (whether so-called distance is it reach galaxy faint distance of in the center to mean) ,This infers with the theory too that conforms.