Jacques

Sayonara There is no direct observation of black hole. By definition a black hole can not be observe. Black hole were predicted by theory and when astronomer found some hight energy phenomena that were not explainable otherwise, they assigned that to the effect of a blackhole. THe center of galaxy where the stars goes to fast, the X-ray comming from these region are all attributed to the effect of a black hole. These effect could also be attributed to a very very dense object, but an object that doesn't go to the limit of the blackhole predicted by theory. My questionning is that from the general relativity principle how can a black hole ever form.

So nobody can explain how the big bang is possible except a cue from the Rebel

I think that C was mesured

I just thaught that the planet of the solar system have small eccentricity: maybe the second focis is in the sun. I found the orbital element of the planet and of the sun. JPL's solar system dynamics WWW Mean Orbital Elements The sun have a diameter of 1,390,000 km. Quick calculation: e:=eccentricity c:=half distance focis a:=semi-major axis e=c/a => 2c=2ea The less eccentric orbit is Venus and it gave a distance betwen the 2 focis of 1,450,000 km. Earth 5 millions km (eccentricity=0.016) So no the other focis is not in the sun. It's somewhere betwen the sun and the planet. Is it a special point ? Mathematically YES Physicaly ? I don't think A good thing about this forum is that it force me to use some little math something I didn't do since a long time. I always been interested in astronomy from a general point of view. I know many different concept without much math around it. Elementary math for many people, here in this forum. I am new here and happy to exchange with you! So much thing to learn and unlearn...

Your right there were other theories that where abandoned. May be these theories would benefit of the new data about the dark energy ??? Why does the discovery of the cosmic background radiation putted an end to Hoyle theory ? Thanks

Ed84c We are viewer on the outside and I understand that the radiation from an object falling in the hole will be more and more redshifted. Also we will see the object going slower and slower. Do you agree with that ? Can you elaborate a little more. I am trying to imagine but I need more informations to figure what you mean.

The point here is that maybe the bigbang doesn't need to have occured in order the see what we see today. The size of the universe may have been the same as today. Matter was almost evenly distributed with only small empty region. Gravity started to act because of these small pertubation. The empty region started to grow and the zero point energy (dark energy) started to act.

To have a blakhole we need enought mass in a small volume. A neutron star with more than 3 solar mass will do. The gravity is strong enought to overcome the repulsion of neutron http://hyperphysics.phy-astr.gsu.edu/hbase/astro/blkhol.html But something is bugging me. Relativity tells us that the more intense the gravity the slower time is going. From our point of view we would see the collapse of the neutron star going slower and slower until the Schwarzchild radius is attained. At this radius from our point of view time will almost be stopped: it will take an infinite amount of time for the collapse to finish. If the universe have existed a finite time how can blackhole have formed?

Hi I had a thought that I would like to share and have your opinion on it. After Hubble discovered the expansion of the universe, the only explaination to it was that the expansion came from a big explosion: the Big Bang theory was born. Now we have other data from the distant supernova survey that tell us that the expansion is accelerating and to explain it we supposed some kind of dark energy with quality opposed to gravity, some kind of repelling force. Here is my thought: with dark energy we don't need to suppose a big bang. The rought picture of the motion in the universe is: A) at big scale we see things going away from each other (dark energy) and B) at small scale we see things going toward each other (gravity). If we reverse that motion and go back in time we will see: A) at big scale a contraction (the inverse of expansion caused by dark energy) B) and at small scale an expansion (the inverse of gravity). The big void between galaxy cluster would shrink and the matter will spread. At some point in the past we may see an almost homogenous matter distribution. I don't know if you see the picture, don't hesitate to ask me and I will try to explain it more. I don't have the math and numbers to verify if it's mathematically possible, maybe someone here can. Thanks Jacques

Thanks Severian for the links! This bring an other question: why does the cosmological constant add up instead of subtracting. The dark energy accelerate the expansion of the universe contrary to matter. It is some kind of anti-gravity. Gravity addup in the equation so why does "anti-gravity" doesn't subtrac ? Thanks again

The jet seen in pictures of galaxie where there is supposed to a black hole doesn't come from it. It come from matter falling on the blackhole that are accelerated by the intense gravity and funelled by the rotating magnetic field that exist around the blackhole. The evaporation of black hole is more of a quantum nature. I am not familiar enought with this Hawking radiation to explain it but maybe someone else here can do it.

The force of gravity is inversly proportional to the square of distance. The expansion increase the distance between object. So the force of gravity will decrease with time and will never be able to overcome the expansion. If the expansion was decelarating then it would be an idication that gravity may take over, but the observation are indicating the contrary

I see that the 'blackhole' word created confusion and nobody understood what was my question. I will try again without using the word 'blackhole' At the beginning (not at time 0, but a little bit after) all the mass of the universe was concentrated in a small volume. The escape speed of that mass was greater than c (the speed of light). Nothing can go faster than c. Then how can anything have escaped out of there ?

OK The confusion came from the word 'certain' that I interpreted has a particular point.

From ed84c The supernovae survey indicate that the expansion of the universe is accelerating. If it is accelerating the expansion will last forever so it is open. Do you understand what I mean ?

What I think is that there is no 'fixed universe center' .

If the expansion of the universe is accelerating does't it mean that the universe is open ?

ed84c I think that the most scientist thinks the universe is open.

Hi At the Big Bang period all the mass of the universe was contained in a very small volume. I think that the density and mass is enought to consider the universe at that time has a black hole and from a blackhole nothing can go out. Then how is it possible that the Bigbang happened ? Do we live in a blackhole ?

away from a certain point sugest to me that there is a center for the expansion

I see more the expansion of the universe away from every point. Go to any point in the universe and you will see the expansion happening te same way. Just a thought

OK The CMB is not a reference system but is used to create a reference system. OK Thanks

In an other thread Martin told I have difficulty to imagine the microwave background like a reference system. Microwave are radiations and radiations are not fixed in space... Can someone help me understand that one ? Thanks

That make sens to me!

No such thing has the center of the universe. To find a center we would need to find some edge.