Imagine what it must have been like to look up at a moonless and clear night sky in preindustrial times. Perhaps a few thousand stars would fill the sky and perhaps you would wonder how far away they were. Figuring that out has taken a lot of time - the size of the known universe has expanded dramatically and cosmology has moved from the religion and philosophy to the physical sciences.
About a month ago came news of the discovery of primordial gravity waves and the possible confirmation of inflation. About the same time a poll that measured public attitudes towards statements on medicine and science was published bringing comments on the low levels of science literacy in the US. While I would agree that science literacy isn't high enough, I found myself wondering what the poll would report if answered by scientists. Polls depend strongly on how questions are asked - for example:
The universe began 13.8 billion years ago with a big bang
I would have problems agreeing and would find myself gaming the survey, trying to guess what it is trying to measure. The age is accurate enough to a single decimal point, but universe did not begin with an explosion of matter into space but rather space itself increases with time. There was a hot big bang, but it wasn't the beginning. And that is going to take a bit of explanation.
Einstein had a problem in 1915. He finally had general relativity, his theory of gravity, but it didn't work for universes that was static. Accepted wisdom of the day was that the universe was static so he made the common mistake we all make - he didn't question everything. He changed the theory a bit by adding a term that allowed it to be eternally static. Later he would say it was his greatest mistake. But someone was willing to see the beauty in the equations and ask the deeper questions.
Alexander Friedmann solved the equations for a general case and discovered the solutions changed with time - the universe had to be changing. Space itself had to be expanding or contracting. He came to the conclusion the universe was expanding. He had discovered, at least in theory, Einstein's general relativity implied an initial state of something infinitely dense - a big bang.1 Friedman published his work in 1922 - a time when the universe was confined to our galaxy and expansion didn't apply. There was no observational verification so it was mostly forgotten.
A fundamental discovery made the observable universe much bigger. Edwin Hubble discovered galaxies like Andromeda were external to the Milky Way and distant on a pervasively unimaginable scale. Specifically he discovered the distance of a galaxy was related to its velocity - the further away something is, the faster it moves. The notion of what the universe was had fundamentally changed.
You would think scientists would be tripping over each other working out where things came from, but that wasn't in fashion at the time - the field was very small and everyone had their own interests. Most of the work concentrated on fleshing out Hubble's discovery. But just after WWII George Gamow considered the implications of a compressing universe that was mostly hydrogen. The gas would compress getting hotter and hotter until the electrons were stripped from the hydrogen atoms. The resulting plasma would be about as hot as the surface of the Sun and opaque. Turning time around and considering Friedman's model you could imagine a hot big bang that expanded cooling to the point where this plasma ball turned back into hydrogen atoms complete with their electrons and the universe became transparent expanding and cooling as time went on. The important feature was that there would be a glow from this period - one that could be detected as a radiation spread throughout the universe. Fifty years ago Penzias and Wilson discovered that afterglow in their work at Bell Labs and the hot big bang had been confirmed.
It was possible to work out a lot of physics. The first few minutes after the big bang had such a high density and temperature that a few elements were forged - hydrogen, helium and lithium. Gravity caused the cooling gas to collect in great clouds forming stars and large groups of these clouds and stars formed galaxies. Lot and lots of detail that you'll find elsewhere.2 The Friedmann/Gamow/everyone-else big bang is a spectacular achievement of the human mind.
but there were a few nagging problems...
Without getting technical one problem, known as the horizon problem, is we would expect a much larger differences in the temperatures observed in the cooling plasma that became transparent about 400,000 years after the big bang. Another class of problem is the flatness problem. Again it gets technical, but a Friedman big bang implies an early density that has to be very accurate. If you look at the density a billionth of a second after the event the number has to be accurate to 24 decimal places. A difference of 0.000000000000000000000001 either way will cause the universe to collapse after a few hundred million years or less, or to expand so much that galaxies and stars would never have formed. And a few other somewhat more technical issue along with the big one of not knowing how the hot big bang worked. Not very satisfying to say the least.
The solution that may work is astounding and conceptually simple, although it is a bit mind wobbling. There are several heroes - if the results are confirmed, and that is always a big if in science, you'll hear their names read in Sweden.
Imagine a volume of air that weighs a gram. If you double its volume, assuming no new air has been added, its density halves. Keep doubling the volume and the density rapidly drops to nearly zero. But what if we had something that didn't dilute - what if we doubled its volume and the density remained the same? It turns out Einstein's equations allow such a process. Guth proposed a very rapid doubling very early on in the age of the universe. It began with a very small amount of mass and volume doubling once every hundredth of a trillionth of a trillionth of a trillionth of a second (10-38 seconds per doubling) and going through something like 260 such doublings to create all of the mass in the known universe. It started out very small with a tiny mass and a size much smaller than the smallest known fundamental particle and stopped leaving the mass of the universe that was on the order of a centimeter across - think the size of a small grape. As the initial inflation stopped, the tiny universe heated dramatically and the hot big bang proceeded ultimately leading to the creation of - well - everything we see.
In a short time I can't go into why the nagging problems were solved. Rather a bit of insight into what appears to be the ultimate free lunch.
OK - I lied when I said I wouldn't write an equation, but you've all seen it: E = mc2. It falls out nicely from special relativity. You can increase the mass of something by adding energy to it.3 Charge a battery or stretch a rubber band and its mass will increase by a tiny amount. Release some energy and its mass reduces. The effect is not huge in our normal experience - adding 25 kilowatt-hours of energy, any form of energy, to a system increases its mass by a microgram - but we notice it with considerable drama in nuclear reactions.
Gravity is an attractive force, but general relativity doesn't talk just about mass and gravity - it also talks about pressure. In general relativity a positive pressure causes an attractive gravity. A gas has positive pressure - you have to supply energy to compress it. A rubber band, on the other hand, has negative pressure - you have to add energy to stretch it. An inflating substance has a large negative pressure. The energy required to expand our uniform density bog to twice its volume is just enough to double its mass.
Guth found the repulsive gravitational force caused by the negative pressure was about three times stronger than the attractive force caused by the mass, so the net gravity in an inflating object causes it to keep inflating. So the inflating blob produces an anti-gravity that blows it up and the energy it expends in the process creates just enough new mass to keep the density constant. The balance of the total energy of the system hasn't changed even though it is now much larger with much more mass.
The ultimate free lunch.
Very very strange indeed. Inflation not only solved the nagging problems of the hot big bang, but it provided predictions that can be tested. One important one was the very strong gravity waves that are seen in the cosmic background radiation bear the imprint of quantum mechanical fluctuations present at the beginning of inflation.4 Those fluctuations gave rise to some non-uniformities in the universe which, in turn, allowed gravity to selectively pull areas together forming everything we know. Those predicted signatures are what were reported last month from the experiment in Antarctica. We went from knowing about the universe about a minute after the big bang, to a period right at the beginning of the hot big bang and a litle before. If it holds there are many more new questions - the same is true if it doesn't, but the questions shift.
If it does hold there is an interesting and probably likely possibility that inflation didn't stop - that we might be in pocket universe where inflation stopped with an infinite amount of creation taking place. The concept of a multiverse is something that demands attention.
We went from the center of the world being our village with the universe not being much farther than a person can travel in their lifetime, to something not much larger than the earth, to one centered around the Sun and perhaps extending to Saturn, to losing the concept of a Sun centered universe, to the Milky Way and then to our current observable universe. But perhaps reality is much richer than that limit.
There is an important lesson that is told over and over again in science. If something nearly works but has a small set of problems it is often a sign that something deeper and more interesting lurks. Often these leaps are out of reach, but they are the source of the really earth-shaking changes in how we understand Nature.
1 The term big bang was coined by Fred Hoyle in a BBC radio broadcast in the last 40s. Ironically Hoyle believed in a steady state universe. Skipping over history a bit, Georges Lemaître came up with a similar solution a bit later. At the time both Lemaître and Friedman were largely ignored. Some ideas come a bit early and in all fairness there are an enormous number of ideas which never work out. A hypothesis should make testable predictions in order to being taken seriously.
2 A rough summary is there was a hot expanding core about 13.82 billion years ago. For the first few minutes it was a hot fusion reactor producing about three quarters hydrogen a quarter helium and bits of lithium. Expansion cooled the universe to the point where fusion stopped. Around 380,000 years ago the hot plasma cooled and became transparent. Radiation from this surface, heavily red-shifted - is the cosmic microwave background - note it is not from the big bang, but a visible artifact of it. Clumps of matter were pulled together by gravity forming galaxies, solar systems and so on. Some of the stars supernoved spewing heavier elements into space. These heavy elements became part of a new generation of solar systems that allowed chemical complexity. At least one of these had the conditions to allow life to form.
3 E= mc2 is the simple form of the equation for energy E and a rest mass m. There is a deep relation between mass and energy. A misconception is that mass must be destroyed to produce the energy in a nuclear reaction, but the energy release is just the difference in the masses of the initial and final bits of the reaction.
A more complete form relates energy, mass and momentum: E2 = (mc2)2 + (pc2)2.. a lovely short video by MinutePhysics gives a good explanation.
4 This may offer important insight into the potential linkage of the quantum mechanics and gravity.
5 Common usage of the term implies something speculative. Anti-science groups exploit this difference to their advantage.
There are many ways to do split pea soup. Here is a rough outline of one I made the other day. A trick for olive oils is unless the flavor is very important, you can get away with something cheap.
Split Pea Soup
° 2 cups split peas
° 1 large stick celery, finely chopped
° 1 medium onion, finely chopped
° 1 cup diced carrots
° 2 tbl olive oil
° 1/3 cup dried barley
° 2 bay leaves
° 1 tel Tamari soy
° 1 to 1-1/2 tsp salt
° black pepper to taste
° sauté the onion in olive oil 'til it is transparent in a large pot
° add 8 cups of water and bring it to a boil, add 4 cups of water to a smaller pot and bring it to a boil
° add peas and bay leaves to the large pot and cook until the peas break apart easily - about 45 or 50 minute for me. Stirring more towards the end
° add the barley to the small pot and cook until tender - about 45 minutes
° cook the carrots in a small pot of salted water until tender, drain and set aside
° when the peas are tender, remove the bay leaves. Now blend the peas until smooth with an immersion blender or in a blender (I prefer immersion blenders - less chance of spilling disasters). If you want something a bit chunkier just whisk away as the peas will break apart nicely.
° strain the barley and add to the soup with the carrots and Tamari soy. Salt and pepper as you like it.