Please tell me about the Dark Energy in a simple way?
953054
people call "dark" what they cannot "see"".To "see" means to detect by means of their eyes that part of electromagnetic waves which we call "visible light".But there is much more "energy" than that.
260891
Well, people have been spotting and reporting MACHOs for a long time, simply by how they affect light that passes through them.\n\nI believe that WIMPs, if they exist, would be the source for more of the energy density requirements to keep omega at ~1. MACHOs only exist within galactic halos, and are aggregated. WIMPs, on the other hand, are likely to be evenly distriubuted within and between galaxies, acounting for their rotation and their movements relative to one another. I think the lack of information about WIMPs is simply due to the limits of our technology in being able to detect particles that only respond to gravitational fields and require a lot of energy to make because they are heavy. If a particle does not interact with any force at all except gravity, it is likely to be a long time before we ever prove that it exists.\n\nI also think that the fermionic superpartner to the Higgs boson is a good candidate for the WIMP, and it is likely that the debate on the existence of supersymmetric particles will be put to rest as soon as those giant particle accelerators are built in Europe. I think the one is supposed to be online in 2008.
44234
Well there are lots of things I do not completely understand about the structure of the universe. \n\nFor example, some current theories are that our 4 dimensional space-time continuum is just part of a higher dimensional entity, where some of the other dimensions are rolled up. However, the time dimension of our 4 dimensional environment is clearly much different than the spatial dimensions, since we appear to only be able to travel in one direction along the time dimension, although many of the equations capturing the physical laws of our universe are invariant when we replace time with -time.\n\nThe expansion that people refer to when they say that the universe is expanding refers to the entire 4 dimensional space-time continuum and possibly some  of the other dimensions as well. This gets very hard to visualize. What I do is think of us as ants living on the surface of a balloon that is being slowly inflated, so the dimensions of the balloon are increasing, and distant parts of the ant's space are becoming increasingly distant. However, this is probably a very limited analogy. \n\nTo get a better picture, you need to consult someone who has thought very hard and very carefully about what the universe is, or supposedly is.
72281
go to \nhttp://www.pbs.org/wgbh/nova/elegant/dimensions.html\nand/or watch The Elegant Universe (NOVA)
832747
Yes, because the cosmological constant is a specification of a pressure that's constant in each unit volume of empty space.  So it "explains" an expansion over and above the expansion due to the velocity imparted by the Big Bang.  Einstein, after some thought, concluded that the CC = 0; in other words, that the expansion of the universe is due only to the initial kick of the Big Bang and is thus slowing down due to gravity.  But recent observations (of very distant supernovas) indicate that the expansion is not slowing down, but increasing.  This is consistent with a small but positive CC.  Other explanations are possible, though.  For example, there could be a "real" force exerting the outward pressure ("real" as opposed to the very mysterious constant pressure per unit volume); if this is true, such a force couldn't be one of the four known forces of physics, but would have to be a fifth one, and so has been called "quintessence."
425304
The idea is that we use a particular type of supernova (type Ia), as a calibrated candle.  By looking at how the supernova dims over time we known intrinsically how bright it was, and thus how far away it is, helping to link the particular redshift distance it is at.\n\nAfter two groups independantly studied these "high-z" events, they both came to the same remarkable conculsion:  By getting measurements of how the universe was behaving long ago (from these high-z events), they see that the universe is actually expanding faster today than it was back then.  The expansion of the universe is accelerating.\n\nThis cause everyone to stop and think - what is causing the expansion?  Couple this result with recent WMAP results about the structure of the universe, and you find that your best models describe the universe today being dominated (from an energy standpoint) by what now goes by the name "dark energy," an energy-like term that drives the acceleration of the universe.\n\nNow where does the cosmological constant fit in?  Well if you put Einstein's cosmological constant back into the equations of universal expansion, you can set a value of it so that the expansion matches what we observe.\n\nLong story short, every type of energy makes the universe behave a ceratin way, at very early times the universe was dominated by radiation, later it was dominated by mass, now it seems that we have eneterd an era that is dominated by dark energy, and a cosmological constant is curenyly a pretty good mathematical solution to this.  What is it "really?"  Don't have a clue, but there is a nobel prize waiting for someone to figure it out.
51809
The correct answer is that no one knows.  We don't even know what most of the universe is made of (right now it's being called dark matter, because all we know about it is that we can't see it).\n\nIf I had to make a bet, I would go with total energy equals zero.  \n\nThere is a lot of matter in the universe, as everyone is saying, and that makes for a lot of mass energy.  But, the flip side is that there is a lot of mass in the universe, and that makes for a lot of negative gravitational potential energy.  It is possible they cancel.
431798
It is completely unknown, since we cannot measure it and have no examples-we dont even have any proper theories, since there is also dark energy, and we dont know which of the effects we observe are due to dark matter and which due to dark matter.  We do suspect that dark matter generates gravity, and perhaps generates and anti-gravitational force (though normal mass may also do this at large enough distance)  We also know that it does not seem to block any kind of electromagnetic wave, nor does it generate any that can be detected, so it isnt just something like dust clouds or large planets without stars.
952552
assume 10^11 stars in 10^11 galaxies at 2x10^33 grams each per star and ~4.6x10^23 atoms/gram (remember, the uni is 10% helium).  This'll get you within an order of magnitude or so.\n\nNote that this is number of ATOMS which appear to represent perhaps only about 5% of the total mass of the universe, most of the rest being dark matter (25%) and dark energy (~70%).
285273
The Universe IS Infinite !!! \n\nThe shape of the universe is determined by a struggle between the momentum of expansion and the pull of gravity. \nThe rate of expansion is expressed by the Hubble Constant, Ho, while the strength of gravity depends on the density and pressure of the matter in the universe. If the pressure of the matter is low, as is the case with most forms of matter we know of, then the fate of the universe is governed by the density. If the density of the universe is less than the "critical density" which is proportional to the square of the Hubble constant, then the universe will expand forever. If the density of the universe is greater than the "critical density", then gravity will eventually win and the universe will collapse back on itself, the so called "Big Crunch". However, the results of the WMAP mission and observations of distant supernova have suggested that the expansion of the universe is actually accelerating which implies the existence of a form of matter with a strong negative pressure, such as the cosmological constant. This strange form of matter is also sometimes referred to as the "dark energy". If dark energy in fact plays a significant role in the evolution of the universe, then in all likelihood the universe will continue to expand forever.  \n\n\nThe density of the universe also determines its geometry. If the density of the universe exceeds the critical density, then the geometry of space is closed and positively curved like the surface of a sphere. This implies that initially parallel photon paths converge slowly, eventually cross, and return back to their starting point (if the universe lasts long enough). If the density of the universe is less than the critical density, then the geometry of space is open, negatively curved like the surface of a saddle. If the density of the universe exactly equals the critical density, then the geometry of the universe is flat like a sheet of paper. Thus, there is a direct link between the geometry of the universe and its fate.
265314
Might be better to be more specific and tell us the question.  It is hard to just give you information on space - seeing as it is infinite for starters.
161557
Dark matter exists in two forms: neutrinos and neutralinos. Neutrinos are what is known as "hot dark matter" (HDM) and neutralinos are "cold dark matter" (CDM). Neutrinos are simply tiny particles with barely any mass that are created when a neutron decays to a proton (beta decay). We know they exist and have detected them. Neutralinos, on the other hand, have not yet been detected. The theory is that they are a form of supersymmetrical particle (or an "evil twin" of a normal particle) that is very heavy, very slow, and requires huge amounts of energy to create - which is why we haven't been able to detect them in particle accelerators yet. Some people say dark matter is just a fudge factor and propose "improved" calculations of gravity to compensate.\n\nDark energy is simply the result of quantum fluctuations. Quantum fluctuations are just waves of gravitational and electromagnetic fields that oscillate over time and cause virtual particle pairs (a particle and an antiparticle) to pop in and out of existence). These fluctuations cause empty space to push outward in all directions, keeping the universe flat and causing it to expand.\n\nIf your still not entirely sure what dark energy is, here's an excerpt from my research paper on dark energy that I am currently working on:\n\n"...the universe is presently in a state of accelerated expansion powered by dark energy, a force that threatens to stretch out everything in the universe until it either freezes or rips apart. Dark energy actually refers to the “vacuum energy” or “zero-point energy” generated by quantum fluctuations (Krauss and Turner, 2004). The fundamental concept of quantum theory is that it forbids intermediate states of energy between fixed quantum values (Barrow, 2001). Just as an electron is forced into a particular atomic orbital (see Figure X), a quantum fluctuation has to have a whole number of wavelengths (n quantum wavelengths, where n is a whole number) (Barrow, 2001). It cannot have half a wavelength or any other fraction and it has to start at zero amplitude and end at zero amplitude (Barrow, 2001). The pressure generated by these fluctuations has been observed in an experiment involving two metal plates positioned exactly parallel to each other in a vacuum (The process is illustrated in Figure XI). Within a region of space that contains the least amount of energy and matter possible, called the vacuum state, quantum fluctuations are present in all possible wavelengths, as seen on the outside of the two metal plates in the figure (Barrow, 2001). When two uncharged metal plates are put into the vacuum, only the quantum wavelengths can be present between the plates (Barrow, 2001). The closer the plates are together, the fewer quantum wavelengths are possible between them (Barrow, 2001). The result is a negative pressure inside the plates that pulls them together, given by the equation\n\nPCASIMIR = ((PI^2)hc/240d^4)A(2)\n\nwhere h is the Planck constant, c is the speed of light,  d is the distance between the plates, A is the area of the plates, and PCASIMIR is the pressure due to what is referred to as the Casimir Effect (Bordag et al., 2001).\n\nThus, dark energy is a simple concept that has a lot of complex problems to solve. As mentioned earlier, it must keep the universe flat and allow its expansion to go from deceleration to acceleration and have negligible interaction with matter (Bauer and Seidl, 2005).\n\nPreliminary attempts to quantify dark energy based on the equation for the fluctuation of quantum fields in the vacuum state, \nu = 2  [(hc |k|)dk]/[2(2PI)^3](3)\n show that such energy would tear apart all matter in the universe (Milton, 2004). Equation (3) indicates that the energy density, u, is proportional to the Planck constant multiplied by the speed of light integrated over a range of quantum fields (represented by the photon wavevector, k, in this example) (Milton, 2004). Eve
631597
Just one doubt about your  theory,how do you know that only one big bang has taken place as you say that a second one is coming up???And tell me how you would accelerate something to the speed of light as the mass would become infinite.\nAnd according to your theory the total energy in the universe will go on increasing.You are stuck in a viscious circle!!!
258993
This looked interesting but I am still very confused ?!?!?!\n\nWeighing the Universe \n\nThere are obvious contributions to the density of the Universe, e.g., planets, galaxies, ... , however, there are also other not so obvious contributions. We need \nrho = rho(baryons) + rho(neutrinos) + rho(photons) + ... \n\nUsing the above, we define \n\nOmega = Omega(baryons) + Omega(neutrinos) + Omega(photons) + ... \n\nSo the issue becomes what are all of these contributions to Omega? \n\nBefore we go on, photons are in there, but why? Aren't photons massless? And what if neutrinos turn out to be massless? Why are they there? \n\n\nAccording to Einstein, E = mc2, and mass and energy are equivalent. They are just different forms of a single entity \n===> mass = Energy / c2 \n\n\nCMBR ===> rho(photons) = 4.7 x 10-34 gm per cubic centimeter << than any reasonable rho(critical) \n\nThe neutrinos are more problematic. \nFor the Cosmic Neutrino Background Radiation (CNBR) \n\n====> rho(neutrinos) = 0.3 rho(photons) and if neutrinos are massless (like photons) then the CNBR does not make a large contribution to the density of the Universe. \n\n\nWhat if neutrinos are not massless? \n\nnumber of neutrinos per c.c. is N(neutrinos) ~ 375 per c.c. ===> rho(neutrinos) ~ 375 m(neutrino) gm per c.c. \n\nTo get an idea about when neutrinos are important, let's use H(now) ~ 25 [km/s] per Million light years ===> rho(critical) ~ 1.2 x 10-29 gm per c.c. ===> rho(neutrinos) > rho(critical) if m(neutrino) > 3.2 x 10-32 gm ~ m(electron)/300,000 (or so). \nNeutrinos can either be important or not depending upon whether they have a significant rest mass. \n\n\nGalactic Masses (Individuals and Groups) \nI will discuss galaxies as probes of the mass of the Universe. In some cases, there will be direct counting of galaxies, in other cases, the galaxies will be used as test particles. Define \n\n\nOmega(gal) = Omega(baryon) + Omega(other?) \nWe will measure Omega(galaxy) using light and dynamical techniques \n\n\nLight Method \nThis is straight-forward. We simply count up galaxies. The complication is that we observe primarily the galaxies which are easy to see. However, there are also many galaxies which are hard to see. These hard to see galaxies are the ones with low surface brightness (which means that they are very hard to see against the pervasive background of the night sky. The number of these low surface brightness galaxies is not yet well-established, however, the current density distribution of galaxies is interesting. But anyway, let's press onward under the assumption that we may be making a factor of 2 error or so by only considering the bright galaxies in our discussion. \n\nRecall, galaxies are divided up into different types: \n\n\n \nThe different types of galaxies have different Mass-to-Light (M/L) ratios. To get a feel for what M/L tells us, consider: \n\n\nA galaxy made of 1011 stars like the Sun. We then have M/L = 1011 M(Sun) / 1011 L(Sun) ===> M/L = 1 M(Sun)/L(Sun). If we measure M/L in units of solar masses to solar luminosities, then this galaxy has M/L = 1. \n\nSuppose that this same galaxy had in addition to its stars, 1011 black holes of mass 1 M(Sun) ===> M/L = 2 x 1011 M(Sun) / 1011 L(Sun) ===> M/L = 2 \n\nSuppose that we had a galaxy composed of 1011 stars of mass 10 M(Sun) and 104 L(Sun) ===> M/L = 1011 x 10 M(Sun) / [1011 x 104 L(Sun)] ===> M/L = 0.001 \n\nThe Mass-to-Light ratio depends on the types of stars that populate galaxies and how much unseen matter exists in the galaxies. \nThe typical M/L for the visible parts of galaxies are: \n\n\nEllipticals: (M/L) ~ 7 - 20 \nSpirals: (M/L) ~ 3 - 5 \n===> Omega(gal,visible) ~ 0.007 (factor of 2 uncertainty) << 1 \n\n\nDynamical Methods \nThe dynamical methods are indirect in the sense that you do not count-up things. You rely on Newton's laws of physics and gravity. The dynamical methods are applied on all scale
1165052
all the energy that is in the universe came from the Big Bang and the universe today is expanding, though a lot slower than before.\n\nHow do we know this? Astronomers have been using spectrometers to chart the temperature from the center of the universe onwards. As you may already know, the farther we look into space, the farther back in time we are looking. What we found, astonishingly, is that the temperature of the universe was hotter before and is slowly reducing. \n\nRight now the temperature is 3 Kelvin (-270 degrees Celsius) in deep space (deep space defined as one atom per cubic kilometer). It shows that energy is continually dissipating, leading to the expansion of the universe, which is leading to a slow decrease in temperature. So there is overwhelming evidence stating that all energy in universe came from the Big Bang and is contained.
985553
There has been many interesting developments on this topic lately :) Over 95% of our current universe is unknown; visible matter (consisting of stars, galaxies, planets... so on) make up mere 5% of our universe. Scientists currently believe that dark matter (type of matter emits little electromagnetic radiation) make up 25%, and mysterious dark energy, which is a type of unknown energy that permeates all throughout our universe with strong negative pressure, make up the rest (~75%). \n\nDark matter and dark energy had been just hypothetical till recently (I mean just last 5 years) when compelling evidences for both were discovered out in space. However, scientists still do not know for sure what makes up dark matter or energy. The ultimate fate of our universe will depend heavily on what these two unknown things turn out to be, as they make up more than 95% of our universe. Right now, the expansion of our universe seems to be winning; scientists discovered that the expansion actually began accelerating since the first couple billion years after big bang due to dark energy. Lots of new things are being discovered, though, and the final answer to your question is still somewhat uncertain.  :)
313486
your answer is in \nhttp://en.wikipedia.org/wiki/Big_Bang