In the 1920s, the universe as thought to be limited to the Milky W ay Galaxy.
Hubble changed it all when he found stars that have always the same luminosity
independently of where they are in space. They are variable stars, also
called Cepheids, whose luminosity grows and is dimmed over time. The duration
of a complete cycle is linked to their brightness. By measuring the length
of the cycle one can calibrate their brightness and determine their distance.
By observing the cepheid in the Andromeda spiral nebula he found that it
was a million light-years away from us, and this means that it is outside
the Milky Way Galaxy. A later, more precise measurement, found that this
star was 2 million light-years away! Hubble made more measurements on other
spiral nebulae and he found that all of them were outside the Milky Way
galaxy. This meant that the Milky Way was only one galaxy among millions
of others and the universe was billions of light-years across.
By using the Doppler Effect, Hubble found that the galaxies are moving away
from us, and that their speed increases with their distance, the ratio between
the two is a constant known a "Hubble Constant H".
- Is the universe all there is? In principle, the universe is all there is but we cannot observe all of it. As cosmic expansion increases with increasing distance from us, some far-away galaxies must travel from us so fast that their light will never reach us. 16bn light years is the limit of the visible universe, what the scientists call its boundary. However there could be an infinite number of universes beyond this limit; this concept is known as "multiverse."
- Weight of the universe? To know the mass of the visible universe we must know its volume and the density of the matter in it. Deep space is mainly empty with an average of a subatomic particle for each cubic metre. As the universe is about 30bn light years across, and assuming that each sub-particle weight as much as a proton the weight of the universe is about 10 trillion trillion trillion tons.
- Was the Big bang a noisy event? Hydrogen and ionised gas filled the early universe so the Big Bang could be heard. But its noise was at a very low frequency that human beings can not hear it.
- Shape of the universe? There is no definite answer to this. According to Einstein's theory, the shape of the universe depends of the amount of matter in it. If there is little matter, the gravitational field will curve it in a sphere. If there are more matter, it could be more like a flat sheet of paper or, with still more matter, like a saddle. At the present time scientists believe that the universe is like a big, flat multidimensional ever expanding sheet of paper.
- Colour of the universe? By averaging the colour of the billions of stars that are in each of the 100bn galaxies, scientists obtained a dull beige shade.
- Where did the Big Bang take place? The Big Bang did not only create matter and energy, it also created space and time. This means that the Big Bang took place everywhere in the universe and they can still be detected in the whole of space.
- What triggered the Big Bang? We really do not know as all the theories and equations break down at the singularity described as the big Bang.
- Was the universe created for us, human beings? Considering the whole
of the universe the answer is No, as we cannot live in most of it. However
the earth seems to have been made specifically to support life.
- Could human beings create a universe? Some scientists believe that we
are on the verge of being able to create tiny universe in laboratories.
An answer to this question could be obtained quite soon.
- What is there between the galaxies? In the vacuum between the galaxies there is what is called Dark Matter. Part of it is ordinary dust and gas, but scientists have found evidence that this conventional matter does not explains everything, far from it. Black holes are only part of the explanation. The present theory is that in space there is a new kind of weakly interactive massive particles or "wimps" that have never been detected on the earth. In addition scientists are convinced that dark energy fills the space. Again we presently do not know what it is but it is a necessary requirement to explain why the universe is expanding at an increasing speed despite the effect of gravity. It is like this dark energy produces some anti-gravitational force out of nothing. Scientists believe that dark energy is a manifestation of "quantum vacuum". According to Heisenberg's principle it is impossible to know the exact energy content of a space region over a period of time. In other words there is no perfect vacuum, even region of apparently empty space are filled with energy. However, the effect of the cosmos of vacuum energy -in the form of dark energy- is not clear yet. Until the "theory of everything" dreamed by Einstein is created, we will probably not know the answer.
-What is the ultimate fate of the universe? Until 1915, the universe was seen as static, unchanging, and infinite in age and extent. With Einstein theory of general relativity which viewed gravity as the result of the warping of space and time by matter, all changed. Studies of distant galaxies showed that they raced away from each other and this was the end of the notion of static universe. But there were still a few possible fates for the universe depending on the amount of matter in it. If there is a lot of matter in the universe, its gravitational effect would slow the expansion, reverse it and this would mean that the universe would end in a "Big Crunch". If the amount of matter is smaller that a certain value then the expansion will go on for ever. This seems to be the case following the appearance of dark energy -with his anti-gravity effect- 5bn years ago. But all is not perfect for the people living billions of years from now. The sun will run out of fuel in about 6bn years and our dying galaxy will be isolated from the others and, finally, the visible universe will be limited to the Milky Way. Later on, some trillions of years from now, all the stars in our galaxy will run out of hydrogen fuel and the light will disappear totally. Before that the earth will be too cold for human beings and they will disappear unless they found another planet were to migrate. There is also a possibility that the dark energy that propels the expansion will not last for ever. In this case the universe would collapse until it ends up in a Big Crunch. The energy released in the crunch would probably cause another Big Bang. According to this theory we are living in a cyclic universe, the current one being only the latest of possibly an infinite number of death and rebirth.
- Any aliens out there? There are about 100 thousand million million million planets in the universe so it is difficult to believe that only the earth can support life. Mars is thought to contain water the main ingredient for life. No real evidences have been found yet. However it is more probable that aliens, if they exist, would be very different from us as the living conditions on their planets would be different, even if they allow life, in some form, to develop. It could very well be that only microbes can survive in the local conditions. Extraterrestrial intelligent beings could exist, but none has been found yet. The distance involved prevent direct contact and the best we can hope is to receive some radio, laser or light signals from them. None has been received yet or, better, none has been noticed; if aliens exist we do not know in which way they communicate and this does not help us understanding their signals, if any.
- How could an advanced civilisation escape their dying universe?
- Step 1: They must have a theory of everything (String Theory, M-Theory,
Quantum Gravity Theory,...}. This theory of everything would answer 3 questions@
- Are wormholes stable?
- Are there divergences?
- Can one find large quantity of negative energy?
- Step 2: Find existing wormholes and white holes (if any) and let us hope
that these wormholes have reached macroscopic sizes. White holes -the opposite
of black holes where time is reversed and they are ejecting matter- are
a solution to Einstein's equations but they have never been found yet. They
could be located on the other sides of black holes so that matter absorbed
by black holes is rejected by the white ones.
- Step 3: Send first probes through black holes as they are dangerous. Anything
sent into a black hole stays there unless it can escape to another universe
or to another point in space/time.
- Step 4: First we must sent probes towers black holes to ascertain the
conditions near their event horizons. After one must construct a black hale
in slow motion for experimental purposes. This could be done, in theory,
by injecting matter and energy into a spinning masse of dust and particles
or in a number of spinning dead stars known as neutron stars.
- Step 5: Create a baby universe. If black holes are too unstable and too
full of irradiation to go through, one could try to create a baby universe.
It would not be easy but the total net amount of matter/energy required
could be as low as 30 gr. The amount of matter required is large butut is
balanced by the negative energy from gravitation so that the net total is
low. However a sphere of false vacuum weighting 3 grams has a diameter of
10E-26 cm and a density of 10E80 gr/cm3.
One could also heat a small region of space to a temperature of at least
10E29 degrees Kelvin then cool it down fast. Space/time at this temperature
is unstable and a false vacuum and a baby universe could be created. Powerful
laser beams and particle beams could be used to create these conditions.
The baby universe would be invisible to us as it expands in another universe
but anti-gravity could inflate it to be as big as ours.
- Step 6: Build huge accelerators. A large atom smasher as the Large Hadron
Collider could be used to create such a baby universe. However a much bigger
one would be required to create a parallel universe as big as ours.
- Step 7: A machine based on laser beams and an implosion mechanism could
also solve the problem as implosion creates large temperatures and huge
pressures. This is not easy to do. One could also use a battery of laser
beams installed on he surface of a sphere and firing their beams radially
to, for example, a pellet of lithium deuteride placed at the centre of the
sphere. Later on, the lasers could be installed on steroids and moons of
various star systems. Their beams should be fired at the same time on a
point target whose temperature would become so high that time an pace become
unstable giving birth to another universe.
- Step 8: Build a warp drive machine. A machine such as the Alcubierre wrap
drive machine shrink the space in front of it and expand the space behind
it.
- Step 9: Use negative energy from squeezed state created by laser beams
and uses it to stabilize wormholes.
- Step 10: Wait for quantum transitions. As cooling goes on for trillions
of years, intelligent beings will be thinking more slowly and hibernate.
They could use that time to wait for a quantum event to happen that is for
bubble universes to appear with usable wormhole transitions to other universes.
- Step 11: As a last hope, if macroscopic wormholes and black holes do not
allow transition to another universe, but if microscopic wormholes are stable,
and then the only remaining solution is to inject our information into another
universe to recreate our civilisation there.