tag:blogger.com,1999:blog-7446617232754011315.post7371384436593880036..comments2024-03-18T13:07:41.886+05:30Comments on The Vinod Wadhawan Blog: 2. The Big BangVinod Wadhawanhttp://www.blogger.com/profile/03806139017217746388noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-7446617232754011315.post-61650041332677028692011-12-22T10:39:12.231+05:302011-12-22T10:39:12.231+05:30Thank you for your comment and question. As you ca...Thank you for your comment and question. As you can see from the level of presentation, I am glossing over many important details. My sole aim here was to give a plausibility argument for how something can emerge out of 'nothing'.<br /> The emergence of matter from the early radiation field was a symmetry-breaking phase transition. A field called the Higgs field has been introduced in cosmology to understand this. This field results in the existence of a cosmological constant, which turns 'empty' space into a space that has an energy content. The problem at present is that the predicted cosmological constant has too large a value for a correct understanding of the observed cosmic evolution. It is believed that perhaps the Higgs cosmological constant had a large value right after the Big Bang, resulting in a violent and very rapid expansion (or inflation) of the universe. At a certain stage of this inflation, a cosmic phase transition occurred, which freed enormous amounts of energy. After this prelude of inflation and cosmic phase transition, the normal (much slower) expansion of the universe set in, and has continued ever since.<br /> But there are gaps in our understanding. Even as early as in the 1930s, it was known that gravitational effects in large galactic clusters are much higher than what can be expected from the known amount of matter there. Apparently, there is another, unknown, form of matter that is a full 90% of all matter, as indicated indirectly by the gravitational effects. It is called dark matter.<br /> There is not only dark matter, but also dark energy. Till the early 1990s the generally accepted belief in cosmology was that the universe cannot go on expanding at the current rate; the gravitational pull of all matter must at least slow down the rate of expansion. Two possibilities were conceivable: (i) The average energy density of the universe may be high enough to ultimately stop its expansion, and then cause its recollapse. (ii) The energy density may be so low that it may never stop expanding, but gravity would still slow down the expansion.<br /> Then something unexpected happened. In 1998 the Hubble Space Telescope observations seemed to show that the expansion of the universe is actually accelerating, rather than slowing down. Three explanations have been offered for this: (i) Perhaps the acceleration can be explained in terms of a long-discarded version of Einstein theory of gravitation, the one that contained a cosmological constant. (ii) Perhaps there is some unknown energy-fluid that fills all space. (iii) Perhaps Einstein's theory is wrong, and a new theory is needed that would include a new field that can explain the acceleration.<br /> No matter what the true explanation is, the phrase 'dark energy' was introduced to account for the mystery. It turns out that ~70% of the universe is dark energy. Dark matter makes up ~25%. The rest (including normal matter) adds up to less than 5% of the universe.<br />Further experiments and their interpretations have conjured up the following scenario: Till ~5 billion years ago, the universe was not having an accelerated rate of expansion. Both dark matter and normal matter pull the universe together. But dark energy does the opposite: It pushes the universe apart. Dark matter dominated the early universe, but dark energy overtook the influence of dark matter ~5 billion years ago. As the universe expands, the domination of dark energy over the effect of dark matter is getting stronger and stronger. Why should that be so? One explanation can come from Einstein's general-relativity theory mentioned above, with cosmological constant included. According to this theory, it is possible for more space to come into existence, and that 'empty space' possesses energy. Being an intrinsic property of space, this ENERGY CONTENT increases as the universe expands. This is what made me make the (admittedly speculative and simplistic) statement you have focused on. The phrase 'energy content' may include mass content also, but I am not sure.Vinod Wadhawanhttps://www.blogger.com/profile/03806139017217746388noreply@blogger.comtag:blogger.com,1999:blog-7446617232754011315.post-75046122703508401032011-12-22T08:44:00.861+05:302011-12-22T08:44:00.861+05:30I must applaud your efforts to explain science. Th...I must applaud your efforts to explain science. The following lines in your blog made me ponder.<br /><br />//Such ever-increasing distances mean a build-up of negative energy, which gets compensated by the creation of an equivalent amount of matter.//<br /><br />Does it mean that the creation of matter has not stopped and therefore we could expect more matter created to compensate the accelerating expansion of the universe ?neohttps://www.blogger.com/profile/01979850680649193300noreply@blogger.com