Cosmology 101

Hi Force... Originally this: And in more modern times, this And most recently, this The radiation itself looks like this...Bugger, you try to be clever, and look what I've just found Edited by Admin, : Reduce image width.

Yes, they are. But not photographs of visible light - instead, they are of the the Cosmic Background Microwave Radiation. The horizontal band visible in all three images is the Milky Way Galaxy, unavoidably contaminating the picture of the rest of the Universe, as we're stuck within it.

Wow, you'd have thought that as a cosmologist, I might have known that...

Scalar fields have been part of space-time physics since GR was first published 93 years ago. Einstein's Cosmological Constant (CC) is effectively a trivial scalar field. The template for Inflation, the exponentially expanding de-Sitter space-time discovered a few years after GR was puclished, is driven by the CC. True scalar fields became a serious consideration in Kaluza Klein theories (1920s) and later in Brans-Dicke theory around 1960. In the 70s and 80s, scalar fields were scattered throughout Supergravity, and then onwards in all flavours of string theory and now M-theory. There is nothing new about scalar fields For a scalar field to drive an inflationary period of the Universe is trivial. However, to get the precise type of inflation that is consistent with observation requires a bit more care, and will probably involved a mixture of competing scalar fields. For those of us who have worked with supergravity and string theory, the scalar fields needed for inflation are not the ones we normally considered of old (wrong sign), but that has now been shown not to be a problem.There's a good chance we will see our first evidence of a scalar field in action as the LHC starts delivering results - the Higgs field.

Nonsense. Everything about the Universe is precisely what is required to enable life on at least one planet. To build up sufficient odds of life taking hold on a suitable planet/body, it appears that you require a Universe of this size, age, density, etc. To claim that the Universe is hostile or against life is simply missing the comsological "evolutionary" process that has brought us to this point. It is like claiming the utter hostily of the Earth to life, as life can only occur in a thin biosphere (even allowing for extremophiles) compared to the immense volume present. The immense volume is *required* to generate a viable biosphere. Or the inappropriateness of a Saturn V launch vehicle for manned space-flight, given how little of it is given over to human occupancy. And don't make the mistake of thinking I'm talking about design - this is simply about required precursors.There is nothing mystical, magical, or religious in pointing out that the Universe is utterly perfect for our existence. It's just good old weak anthropic tautology.Moving on to Rahvin's point:If the Earth existed in isolation, in a Ptolemaic cosmology, then there really would be a "fine-tuning" argument for a creator - but we now realise that we live in a "multiverse" of countless planets around countless stars in countless galaxies. These planets allow for innumerable plays at the game of life, and by simple anthropic reasoning, we find ourselves on one of the lucky winning planets.Now sure, tweak around with some of the fundamental constants and you may find in our local vicinity of the "Universal" parameter-space that there are some other possibilities that allow for elements with similar capabilities to carbon/silicon. There may even be far superior element sets that give rise to universes that are teaming with life compared to ours. But most modifications in the parameter-space are going to give not just useless elements, but no elements at all.We're not looking at the Universe as a whole as being finely-tuned for life, it is finely-tuned for some resemblence of "normal" existence - for structure, for planets (or similar), for stars (or similar), and for a reasonable time-scale. Universes that exist for between 1ms and 1Myrs are not going to be much use, whatever structure they may contain. Likewise, universes that live forever by expanding so quickly that individual quanta become causally isolated after a few 10^-30 seconds are not going to be particularly useful for life!It is difficult to have a rigorous measure on these things, but from all of our playing at building models of universes, there appears to be 10^(large number) more universes that are utterly hopeless at producing life compared to those that even get close to producing some form of structure.Some of the parameters may well have natural methods of arriving at their "finely-tuned" values - such as the critical density of the Universe. Inflation naturally generates this precise value. But others (such as the Cosmological Constant) seem to be so far from the values that we would expect, and are intimately tied with our existence (as in, any kind of life, plants, stars, etc.) And even inflation seems to require a precise set of circumstances, and so is possibly not as "natural" as we once hoped.The obvious answer is that just as the coarse high-level parameters relevant for life (mass of planet, distance from star, type of star, age of star, presence of moon, absence of nearby stellar unpleasantness, presence of Jupiter-type, etc, etc) are played out across the Universe, guaranteeing our existence somewhere (maybe as heptapodal gralfinches on Tau Ceti IV) - the fundamental parameters of our Universe are played out over a much larger scale. This is has been the direction that our research has pushed us for some time now - supergravity, string theory, eternal and chaotic inflation, ekpyrotic universes, and now the Landscape of modern string theory/M-theory. We are not short of multiverse theories! And for a long time, we have regarded them as a possible saving explanation for the otherwise apparent fine-tuning of our Universe that allows for "stuff" to exist, never mind life.

Sorry Rahvin, I made a large reply to your post but it ended up being tacked on to the end of a reply to Taz. Please see message 40 for the details.

Effectively, yes. They can appear as a negative energy or a positive energy in their effect upon the Universe, in terms of causing an expansion or contraction. Noramlly a field will fluctuate over all of time and space so there would be no particular overall frequency, but scalar fields in particular do have a habit of becoming "frozen out" at particular values, so in effect they are of a particular frequency.

Good question - first off, there is nothing unusual about scalar fields. On the contrary, they are the simplest type of field. All of the fields that we deal with every day are more complex than scalar fields - they are vector, spinor, and tensor fields. But as of yet, we don't have any direct evidence of a scalar field. The one scalar field we really think exists is the Higgs field, and we're hoping to discover direct evidence at the LHC within the next year or so.

I really don't see the relevance of your request to what you say Ago claimed. If the Universe did have the sole divinely inspired purpose to bring us into existence, it has done its job perfectly well. And Ago didn't even claim this - he said: He's not even sure he's talking about life in general, never mind anything about Earth. He is obviously confused over what he has read, so trying to argue with his misconception of someone else's point seems rather fruitless!Edited by cavediver, : No reason given.

Not so fast A Universe Without Weak Interactions is an excellent paper, with some fascinating insights into screwing around with the Stanadrd Model (not mention it is great as a teaching tool for graduates into how certain features of the SM arise)BUT, it certainly does not demonstrate that random tinkering with fundamental physics preserves the ability to create life-friendly structure. This is one (relatively small) change that is finely tuned by hand to match many of the features of our Universe. It is a potential life-supporting point in the global parameter space, slightly separated from our own Universe. We expect these, and I made reference in my earlier post. Well, in *theoretical* physics, we do have inputs. We have been looking at such scenarios for over thirty years with SuperGravity and its successor, String Theory/M-Theory. There have long been attempts to come up with THE specific string theory arrangement (compactification) that would reduce to something resembling our Universe and the Standard Model. It was remarkably difficult, and made us realise that coming up with our Universe is not as easy as we originally thought. Some of us (those of us fond of anthropic reasoning) believed that this would not be necessary, that there would be a vast array of different compactifications spanning the 10d (now 11d) space-time, and our 4d-Universe would simply arise in some small corner where the merging compactifications would be just right. This has now become mainstream (within the String fraternity) with the concept of the String Landscape. It is the biggest get-out clause ever devised - whatever fine tuning is or is not required for life, it is provided by the Landscape.Edited by cavediver, : No reason given.