The Universe began with a big bang. Not an explosion from a single point, but rather an early dense state. Of course an obvious question this raises is what came before the big bang? While it’s possible that the answer is “nothing,” that hasn’t stopped some theorists from postulating an earlier cause for the Universe. One of these ideas is known as the big bounce. 

The basic idea of the big bounce is that the Universe goes through a series of expansions and contractions. Right now we live in an expanding Universe, but at some point, the model argues, the Universe will start to contract. Eventually it will contract to a dense fireball again, and this will trigger a new big bang. This solves the “what came before” problem of the big bang by postulating an infinite series of big bangs, but it’s not without problems. For one, as we currently understand dark energy the Universe will likely continue to expand forever. For another, if the Universe did re-collapse into a dense state, we have no idea how it would trigger a new big bang.

A new work in Physical Review Letters proposes a solution to this second problem. The key to the idea is to introduce quantum theory into the mix. In a purely classical model, a shrinking universe will eventually collapse into a singularity. It’s long been thought that quantum theory could provide a solution to this problem, but the devil is in the details. To prevent the formation of a singularity, the work introduces a symmetry known as conformal invariance. As long as the Universe has this symmetry during its dense period, it could enter the dense period at the end of one “universe” and re-expand to form a new “universe.” The authors call this a perfect bounce.

So with the right conditions it’s possible that our Universe could simply be the period between bounces.

Paper: Steffen Gielen et al. Perfect Quantum Cosmological Bounce. Phys. Rev. Lett. 117, 021301 (2016). DOI: 10.1103/PhysRevLett.117.021301

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The Universe we see around us has some unusual properties. In every direction we see roughly the same number of galaxies on large scales. The cosmic microwave background has roughly the same temperature in all directions, and the Universe as a whole is topologically flat. In physics terms this means the Universe is homogeneous and isotropic. But according to the big bang model, we wouldn’t expect that to be the case. One way to solve this issue is through a process known as inflation, but this raises some interesting problems of its own.

The observational evidence for the big bang is quite strong, so we know the early Universe was extremely hot and dense. We also know the Universe is expanding at an ever increasing rate due to dark energy. But if cosmic expansion is only driven by dark energy, then it would seem the Universe is too homogeneous and isotropic. There simply wasn’t enough time for the Universe to reach a homogeneous state before things started collapsing under gravity. However, if the Universe had a period of very rapid expansion (known as the inflationary period), any major fluctuations in density and temperature would be smoothed out, and the Universe we observe would be a small fraction of the cosmos. The inflation model was first proposed by Alan Guth in the 1980s, but to understand the model we need a bit of quantum theory.

A false vacuum is a local energy minimum, but not the true minimum.

Physical systems tend to move toward a state of lowest energy. For example, a hot object will tend to cool down by emitting heat and light. The Universe is no exception, and so it’s tendency should be to expand and cool. A system will move toward the lowest energy if it can, but sometimes a system might reach a low energy state that isn’t the lowest possible energy. For example, a ball will tend to roll down a hill, but it might find itself in a shallow dip in the side of a hill. The dip is a local minimum, but the bottom of the hill is the true minimum. For an object like a ball, once it reaches a local minimum it is stuck there. The ball can’t climb out of the dip to keep rolling downhill. But quantum systems can shift out of a local minimum. Through a process known as quantum tunneling, they have a small probability of jumping the gap to reach lower energy.

Since the Universe is fundamentally a quantum system, the early Universe could have found itself in a local minimum, or what’s known as a false vacuum (since a vacuum would be the lowest state for the cosmos). It would stay in this false vacuum for a time before quantum tunneling to the true vacuum. What Guth found was that since the false vacuum state has energy, it could cause the Universe to undergo rapid expansion. Under the inflationary model, the early Universe was in such a false vacuum for a brief period, and thus had a brief period of inflation. The inflation model is actually pretty elegant, and since the  model solves these kinds of problems so well, it is generally thought to be the correct solution. Most astrophysicists figure it is just a matter of gathering enough data to detect its effects.

There are, however, some issues with inflation. One of the big ones is that there are lots of ways inflation could occur, and most of them wouldn’t lead to the type of Universe we observe. They might inflate so much that stars and galaxies never have a chance to form, or not enough to give us a homogeneous universe. There a very narrow range of inflation that would produce a universe like ours, and it seems odd that inflation would just so happen to occur that way. This problem is part of the larger issue of the anthropic principle, where some argue the Universe seems to be configured in just the right way for life to exist.

Eternal inflation would create countless pocket universes.

But a variation of the inflation model may solve the issue. Known as eternal inflation, it argues that the Universe might not collapse from a false vacuum as a single whole. Instead, different parts of the Universe might reach different false vacuums, and they might drop out of that false vacuum at different times. While our region of the Universe seemed to drop out rather quickly, other parts would have dropped out later, and still other parts might still be inflating. This model leads to a kind of multiverse, where there are pockets on non-inflationary universes surrounded by regions that are still inflating. As a result, all the different varieties of inflation would occur. Under eternal inflation, a universe such as ours is bound to occur.

Of course all of this is pretty speculative. Since we don’t have any way to observe the multiverse, we’d need to understand just how eternal inflation could arise. Right now we don’t even have any direct evidence for inflation, and until we have evidence we can’t narrow down the nature of inflation (assuming it occurred). So for now we’ll just have to keep gathering evidence.

Ever onward, ever upward.

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[av_video src=’https://youtu.be/gJJmFnMea1Q’ format=’16-9′ width=’16’ height=’9′]

The cosmic microwave background (CMB) is the thermal remnant of the big bang. It was once a warm glow of about 3,000 K, but as the universe expanded and cooled the CMB gradually chilled to about 2.7 K. As a result, its once orange glow has shifted down to the microwave range, hence its name. Usually the CMB is presented as an image, where various colors represent the small fluctuations in the background, but when it was first observed it was detected as sound.

Because the CMB is in the microwave range, you can convert its electromagnetic waves to sound just as we do with radio. The result is a kind of faint static you can hear above. The sound was captured by Robert Wilson, who with Arno Penzias made the first measurement of the CMB as a blackbody background. It might not sound like much, but the very fact that it’s there was the first definitive proof of the big bang. Throughout the entire universe that faint sound can be heard. It’s everywhere and in all directions.

People often imagine the big bang as beginning with an explosion expanding out of darkness, but that faint hiss shows us that isn’t true. The big bang happened everywhere, and everything we see around us is a product of it.

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Did the big bang really happen? Yes, despite recent claims to the contrary.  A new paper in Physical Letters B has the popular press wondering if there was no big bang, but the actual paper claims no such thing.

The big bang is often presented as some kind of explosion from an initial point, but actually the big bang model simply posits that the universe was extremely hot and dense when the universe was young. The model makes certain predictions, such as the existence of a thermal cosmic background, that the universe is expanding, the abundance of elements, etc. All of these have matched observation with great precision. The big bang is a robust scientific theory that isn’t going away, and this new paper does nothing to question its legitimacy.

That doesn’t mean there aren’t unanswered questions about the big bang. For example, simple big bang models show that if you go back in time far enough, there is time when the entire universe was an infinitely dense singularity. This singularity would mark time zero for the cosmos. As many of you know, singularities are problematic, and they tend to stir up lots of debate. That’s where this paper comes in.

The paper presents a big bang model without an initial singularity. It does this by looking at a result derived from general relativity known as the Raychaudhuri equation. Basically his equation describes how a volume of matter changes over time, so its a great way of finding where physical singularities exist in your model. But rather than using the classical Raychaudhuri equation, the authors use a variation with a few quantum tweaks. This approach is often called semi-classical, because it uses some aspects of quantum theory, but isn’t a complete quantum gravity model (which we don’t have).

You can have a big bang without a beginning. Credit: Ethan Siegel.

What the authors show is that their modified Raychaudhuri model eliminates the initial singularity of the big bang. It also predicts a cosmological constant, which is a proposed mechanism for dark energy. Their model is really basic, but this first result shows that this type of approach could work. The catch is that by eliminating the singularity, the model predicts that the universe had no beginning. It existed forever as a kind of quantum potential before “collapsing” into the hot dense state we call the big bang. Unfortunately many articles confuse “no singularity” with “no big bang.”

While this is an interesting model, it should be noted that it’s very basic. More of a proof of concept than anything else. It should also be noted that replacing the big bang singularity with an eternal history isn’t a new idea. Many inflation models, for example, make similar predictions. But none of these ideas eliminate the big bang, which is an established scientific fact.

Paper: Ahmed Farag Alia & Saurya Das. Cosmology from quantum potential. Phys. Let. B. 741, 276–279. (2015)

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In the standard ΛCDM model of cosmology, the early universe was in a hot dense state known as the big bang. As the universe expanded, its density and temperature dropped to the point where electrons and nuclei could combine to form neutral hydrogen and helium (with small traces of other elements). At that point the light of the universe was finally free to travel great distances through space without colliding with ionized particles. We see that first light as the cosmic microwave background.

After that period (known as recombination) there was no way for new light to be created. The primeval fireball had become too cool to produce new light, and there were no stars to shine. As a result, the universe entered a period known as the dark ages, that spans the time between recombination and the formation of the first stars. Just how long that dark age lasted has been difficult to pin down.

Stars re-ionize material, which interacts with the cosmic background. Credit: ESA

Based on observations such as the Hubble Deep Field, it’s been estimated that the dark ages ended about 400 million years after the big bang.  But new observations from the Planck satellite gives us a much more accurate age of 550 million years after the big bang. This is possible by looking at the polarization of light from the cosmic microwave background. In the last moments before recombination, when the electrons finally started to bond with nuclei, the photons created in the big bang would have one last scatter off an electron before making its long journey across the universe. Because of this the light is polarized, which is one of the things Planck has studied in detail. Throughout the dark ages, that polarization was “fixed” since there was no free electrons for the light to scatter off. But once stars began to form, the new light and heat could re-ionized surrounding material. As a result, some of the light from the cosmic background was scattered again, polarizing it in a different way. This new scattering leaves its fingerprints on the CMB, which tells us when it occurs.

What’s interesting about this new result is that by the time the dark ages ended, stars and galaxies were already forming. This means that by the time stars began to shine the structure of galaxies was already set into motion. The dark ages lasted longer than we though, but it also ended more abruptly than we suspected.

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One of the big points of evidence in support of the big bang is the cosmic microwave background (CMB). It is often described as the afterglow of the primordial fireball, but it is much more than that. As we make better observations of the CMB we not only gather evidence of the origin of the universe, we also get an indication of the specific nature of our universe. One of the ways we see this is through what’s known as the three peaks.

When we look at the cosmic microwave background, one of its distinctive features is that it is a thermal blackbody. In all different directions, it has a temperature of 2.7 K. This is exactly what you’d expect if the universe was once in a hot, dense state.  While the CMB is extraordinarily uniform in temperature, it isn’t perfectly uniform. There are very small fluctuations in temperature. These fluctuations were mapped in detail by the COBE satellite in 1992. Later, more detailed maps of these fluctuations were made by the WMAP and Planck satellites.

Credit: Wayne Hu

These variations in temperature are like ripples on the cosmic pond. By observing these ripples we can determine what was happening in the universe when it was very young, which in turn tells us things about the universe today. One of the ways we do this is by looking at the scales at which temperature fluctuations occur.  You can see this in the figure, where the amount of temperature fluctuations (in microkelvin) is plotted against what is known as the multipole moment (l), which is a measure of the fluctuation scale. Basically, you just take the total average temperature of the whole sky, then split the sky into two regions and take an average of each section, then split and average again, and so on.  Keep doing that, and you get an “average” temperature at each higher multipole scale. When this power spectrum of CMB fluctuations is plotted, you notice a big first peak, followed by two smaller peaks before it dies off in a series of small fluctuations. It is these three peaks that paint a clear picture of our universe.

Credit: moot Cosmology Group

The first peak is an indication of how flat or curved the universe is as a whole. Since the cosmic microwave background comes from the farthest edge of the visible universe, it’s light can be distorted by the cosmic curvature. If the universe is flat (like a flat sheet of paper) then the fluctuations we observe would appear undistorted. If it is positively curved (like the surface of the Earth) then the fluctuations would appear magnified by the cosmic curvature. If the universe is negatively curved (like the surface of a saddle) then the fluctuations would appear smaller.

On the power spectrum curve, this means the first peak would be more to the left if the universe is positively curved and more to the right if negatively curved. What we find is that the first peak is at about l = 200, which the value for a flat universe. Within the limits of our CMB observations, the universe is exactly flat. This means that the universe as a whole is at least 150 times larger than the observable universe. It may be infinite, but at the very least it is really, really big.

The second peak tells us about the amount of matter in the universe. Given the initial fluctuations in the universe, all matter would tend to gravitationally clump toward the higher temperature (higher density) fluctuations, which would tend to reinforce them on smaller scales. But regular matter (the kind that interacts with light) would also tend to heat up as it clumps, and the resulting pressure would tend to push against the clumping matter. So the more regular matter you have, the more pushback you would get. This means that the more regular matter there is in the universe, the more the second peak will be damped. So the smaller the second peak, the more matter in the universe. Given the observed level, we find that regular matter makes up about 4.9% of the mass/energy of the universe.

The third peak is an indicator of dark matter in the universe. Dark matter gravitationally clumps like regular matter, but since it doesn’t interact strongly with light, it isn’t affected by the pressure of light against it. So as the regular matter clumping experiences a push-back, the dark matter clumping does not. So the height of the third peak gives us a measure of how much dark matter there is compared to the total amount of light in the early universe (what’s known as the matter/radiation ratio). Since we know that light and regular matter are related, the matter/radiation ratio tells us the amount of dark matter in the universe. From this we find that dark matter makes up about 26.8% of the mass/energy of the universe.

The universe according to the CMB. Credit: ESA/Planck

Since the universe is flat despite having matter and dark matter, the remaining mass energy must be in the form of dark energy. Without it, the universe would appear positively curved (closed), which we don’t see.  So from observations of the CMB we find the universe is flat, about 4.9% regular matter, 26.8% dark matter, and 68.3% dark energy.  This is found simply from the cosmic microwave background. We have other observations, such as the redshift/distance relation of galaxies, the way in which galaxies clump in the present universe, and a variety of other tests. They all give similar results. In this way we have a confluence of evidence that clearly shows the size, age, and structure of the universe.

But even if all we had was the cosmic microwave background, we would still know quite a bit. And as we gather even more sensitive observations, it will surely tell us even more.

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Recently there was an article by Tim Reyes asking if the standard cosmological model is a Rube Goldberg machine. The idea is that so many ill-fitting ideas have been put together that it seems unreasonably complex.  I’ve used a similar criticism against certain models through the phrase “tweak theories are weak theories.” Given the latest implications that the Higgs field may contradict inflation, and the BICEP2 results may not hold up, should we really think of standard cosmology more as a tweak theory than a robust model?

Credit: Rube Goldberg

The current standard model of cosmology, often called the LCDM model, is basically as follows. About 13.8 billion years ago the observable universe was hot and dense. Then, driven by gravity, dark energy (L for lambda, which is the symbol for dark energy in general relativity) and cold dark matter (CDM) it expanded while galaxies and clusters formed, leading to the universe we see today. Since dark matter is a mysterious material we haven’t seen directly, and dark energy is even less understood, it is tempting to see them as “tweaks” just to make a model work. This urge is particularly strong given that these things aren’t only necessary for the LCDM model, they supposedly make up 23% and 73% of the known universe. Regular matter like planets and us are less than 4% of the universe. A model where 96% of it is hypothetical “stuff” hardly seems very scientific.

But taken from an observational approach, however, the LCDM model seems strikingly robust. There are three main observational tests for the model, which are sometimes referred to as the pillars of the big bang. These tests agree with LCDM to a degree that is almost unparalleled.

Redshift vs. Distance. Credit: Brian Koberlein

The first pillar is the redshift-distance relation. This relation was first demonstrated by Edwin Hubble, using the Cepheid variable period-magnitude relation discovered by Henrietta Leavitt.  By using Leavitt’s relation, Hubble could determine the distance to dozens of galaxies. He then observed their Doppler redshifts to determine how fast these galaxies move away from us. What he found was a linear relation between galactic distance and the speed at which the galaxies move from us.  It was the first evidence that the universe was indeed expanding.

Since Hubble’s first discovery of this relation in the late 1920s, we’ve made ever more detailed observations of the effect. Using the brightness of distant supernovae we can determine the distance of galaxies billion of light years away. From this we found the universe is not only expanding, but that space itself is expanding. Our observational data is now precise enough that we can distinguish between a universe where galaxies are moving through space (like an explosion from a point) and a universe where space itself expands over time.  The observations clearly match cosmic expansion. While this concept might seem quite odd, it is easily describable within general relativity, which has been verified experimentally countless times.

Blackbody spectrum of the cosmic microwave background. Credit: Brian Koberlein

The second pillar is the cosmic microwave background (CMB). Often the expanding universe is imagined as a loaf of rising raisin bread. But just because the raisins are expanding away from each other like galaxies, it would be silly to claim the bread began as a primordial dense state. So why do we assume this for the universe? Because the CMB tells us this.  If the universe did begin hot and dense, then there should be an afterglow of that original heat.   If space is really expanding, rather than matter exploded from a point, then the afterglow should be seen in all directions.  Not only that, the afterglow should appear thermal. In other words, its spectrum should match that of a blackbody. What we find is exactly that. The thermal glow has cooled so that it is now seen in microwaves (hence the term), and it is seen in all directions. Not only does the CMB appear thermal, but it is so close to a perfect blackbody that it is one of the best experimental fits humanity has ever done.

Since the discovery of the CMB in the 1960s, space observatories such as COBE, WMAP and Planck have measured tiny fluctuations in this background. The scale at which these fluctuations occur tell us something of the amount of dark matter and dark energy.  Basically the more dark matter the more fluctuations there should be, and the more dark energy the more spread out these fluctuations should be. What we find from the latest data is that the CMB predicts a universe with about 23% dark matter and 73% dark energy.  This matches the rate of cosmic expansion as seen in measurements of the Hubble relation. So the first two pillars are in good agreement.

Credit: NASA, WMAP Science Team
and Gary Steigman.

The third pillar is perhaps my favorite, and it deals with the abundance of elements in the universe. Since the cosmic microwave background is the light when the universe finally cooled enough to be transparent (known as recombination), we can determine the temperature of the universe at that time. Given our measure of dark energy, we know the rate at which the universe was expanding before that, and therefore we know the temperature of the universe when the first nuclei of atoms were forming. The thing about nuclear fusion is that it is very complex, and it is highly dependent upon the temperature and density of the nucleons. Change the temperature a bit one way or the other, and the initial ratio of primordial elements would be different.  So pillars one and two make very specific predictions about the abundance of elements.

Looking at some of the most distant quasars, we have found two examples where they illuminate primordial gas clouds. We can tell that they are primordial because they don’t contain any trace of heavier elements. When we compare the ratio of hydrogen to deuterium, we find that it agrees perfectly with the prediction of elemental abundance.  Other observations of slightly less pristine clouds find similar agreement for the ratios of helium and lithium.  This is perhaps the most difficult pillar to verify, but all evidence so far agrees with the predictions of LCDM.

Various observations of the state of our universe. The yellow triangle agrees with all of them.

Sometimes a fourth pillar, known as Olber’s paradox, is listed as well, but the big three are the ones that really put LCDM specifically to the test. Beyond that there are other tests such as the baryon acoustic oscillation (BAO) that looks at the distribution of galaxies in the universe as a measure of dark energy, or the Alcock-Paczynski cosmological test, which compares the LCDM model to other possible big bang models. All of these make specific predictions about the big bang, dark energy, dark matter and the age of the universe.  They agree to remarkable accuracy.

This doesn’t mean there still aren’t questions about many of the details. There are some big mysteries, such as early inflation and how the Higgs field comes into play. With new observational data being gathered, there will be a lot of arguments about the details and difficulties. But all of these arguments are not about the LCDM model as a whole. Even if we discover a radical new understanding of the universe, the LCDM model will continue to work amazingly well.

Even with its challenges, the LCDM model is not a “tweak theory”. It is a robust model of the universe supported by a great deal of astronomical data.

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There’s been several science headlines recently stating that “Scientists Claim Universe Shouldn’t Exist.” Which I suppose means we should all just vanish in a puff of logic, or (derp) the scientists have said something stupid again. Needless to say, “scientists” have said no such thing, and what has been said is an interesting venture into cutting-edge theoretical physics. The popular press articles are based on a paper published in Physical Review Letters, which looks at possible connections between the Higgs field (of Higgs boson fame) and early inflation possibly observed by BICEP2. The authors took the mass of the Higgs boson as determined by the LHC (which is a measure of the strength of the Higgs field) and the value of inflation as measured by BICEP2 (which is a measure of the strength of inflation in the early universe). They then analyzed what would happen according to our current understanding of early cosmology.  What they found is that given these two values, early cosmic inflation could create quantum fluctuations strong enough to cause the Higgs field to collapse.  This would effectively collapse the universe, hence the headlines.

A possible collapse of the Higgs field is something we’ve known since its discovery. It stems from the fact that quantum systems don’t always have to settle in their most stable configuration.  They can instead find themselves in a locally stable state (known as a metastable state).  We see this, for example, with electrons in an atom. The stable state of an electron in an atom is its lowest possible energy level, but an electron can be in a higher energy level for a while.  Eventually it can drop to a lower energy level, which releases a photon.  This effect is why we see line spectra in stars and interstellar clouds.

The Higgs appears metastable. Credit: luboš motl

Given the masses of the Higgs boson and the top quark, the Higgs field seems to be in a metastable state. If the top were more massive, it would be unstable, and if the Higgs were more massive, it would be stable. This fact is sometimes expressed by the statement that the universe could collapse into a new quantum state at any moment, but that’s a whole other topic. This new paper simply calculates that given current values it would seem the universe should have collapsed during inflation.

This tells us there is something wrong with our model, and there are several possibilities. One is that the measurements are off somehow. The BICEP2 results (if valid) give a value for inflation that is stronger than expected. If the inflationary period was weaker, then that could be a solution. Given the weakness of the BICEP2 result, it is quite likely that the inflation value is wrong.  Another option is that inflation is simply wrong, but that isn’t seen as very likely.

The authors look at another possibility, that somehow the Higgs field and inflation are connected. This idea has been examined before, but this new paper demonstrates that such a connection could resolve the problem of early collapse.  So what this paper actually does is point in the direction of new physics. Higgs driven inflation could resolve some real problems in the model, and that gives us motivation to explore things further.

Paper: Malcolm Fairbairn and Robert Hogan. Electroweak Vacuum Stability in Light of BICEP2. Phys. Rev. Lett. 112, 201801. (2014)

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There’s a popular picture that traverses the net now and then that states 97% of climate scientists believe that anthropogenic global warming is true. More specifically, that of peer reviewed climate research papers, of the ones that made a statement on the cause of global warming, 97% agreed that humanity was the cause.

You can imagine the lively discussions it induced.

There are certain areas of science that people find deeply controversial. In climate science it’s global warming. In biology, it’s evolution. In astrophysics it’s the big bang, or to a lesser degree things like dark matter. The experts in these fields don’t find these controversial at all. The big bang happened, evolution is real, and humans are a principal cause of global warming.

The researchers in these fields have moved beyond those basic facts and are investigating the details. Did the early universe have an inflationary period, and if so, how long did it last? How did bipedalism arise in early primates? Why is the rate of global temperature increase slower than expected? And yet in the popular press and blogs they are barraged with doubt.

In astrophysics we have it pretty easy. Big bang hecklers usually just argue that we don’t really know because we weren’t there, or that because we don’t know the exact cause of the big bang we don’t know anything about cosmic evolution. We aren’t generally accused of being part of a cabal that only “agrees” on the big bang to support a philosophical or social agenda, or that we’re simply promoting the big bang for the money (although the electric universe people often claim such things). Those arguments are often applied to evolutionary biologists and climate scientists.

This is why you have things like the 97% image. On the face of it, the 97% argument is rather meaningless. It doesn’t matter whether 97% agree or 9% agree. Science is not a democracy. You don’t get to declare what is true by consensus. What matters is what the data tells you. What matters are the theories that work. It also meaningless that 3% don’t agree with anthropogenic global warming. Not every astrophysicist agrees that the big bang is real. I once met a physicist who didn’t think photons exist. I’m sure if I searched hard enough I could find one that thinks the Earth doesn’t move.

What the 97% argument does do is raise a specific question: at what point does a reasonable non-specialist concede that the scientists are right? In the case of the big bang, I can (and have) present the evidence we have for the big bang. If you search the internet you can find evidence arguments against the big bang. I can explain why I don’t find those arguments compelling, and note that the vast majority of astrophysicists find the evidence for the big bang to be compelling.

If you still aren’t convinced, that’s about as far as we can go. You aren’t obligated to believe me, and I’m also not obligated to convince you. But if the reason you aren’t convinced is because you don’t think there’s enough evidence yet, or because you know of a scientist that disagrees with the majority, then you are basically arguing that the majority of experts in the field are either confused or disingenuous. Basically it means you just don’t trust them. Hence the assertion that evolutionists are promoting atheism, or that climate scientists are committing fraud to make money.

Because if 97% of people who have devoted their lives to mastering a scientific field have looked at the evidence and come to the same conclusion. If they are earnest and honest in their search for the truth, and have been convinced by the evidence, then that is a compelling argument that the theory is sound. Without becoming an expert yourself, the only counter is to doubt their veracity.

That might sound like I’m saying there’s no room for dissension from the general public. That you should either agree with “us experts” or you’re an idiot. This isn’t the case at all. There is room for disagreement in science. No theory is above reproach, and it is always possible that new evidence can overturn a long-held theory. But your disagreement does not invalidate a particular theory. Calling anthropogenic global warming nonsense, for example, doesn’t change the fact it’s the best model we have.

Science is about questioning results, but there also comes a time where the evidence we have demands a verdict.

Note: Feel free to comment, but name-calling of particular groups, or of individuals other than myself will be deleted. State your opinions, but be ladies and gentlemen of honor.

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Only about half of Americans are confident in the validity of the big bang. That’s a rather surprising number given that the big bang is not only well supported by the evidence, it is now a foundational concept in modern astronomy.  There are, of course, several reasons for this lack of acceptance, but one I hear often in interactions with the public is the claim that the big bang (and astrophysics or cosmology in general) is not scientific because it is not falsifiable. After all, there is only one universe, and you can’t run that experiment again.

The underlying assumption of this assertion is that if you can’t do a repeatable experiment in a lab, then it isn’t science. Science is apparently what is performed in the here and now, and over and over. This is contrasted with “historical” science such as cosmology or evolution, where untestable theories are inferred. Thus the big bang is just an idea, not a scientific theory.

Except that isn’t how it works. It’s true that in a broad sense falsifiability is a necessary aspect of any scientific theory, but that doesn’t have to come from repeatable experiments. An often cited example is the statement that “all swans are white”.  Find a single black swan, and you’ve invalidated my swan theory. Finding a second black swan doesn’t change that fact.

So is there a realistic way that the big bang model could be falsified? Sure.  One way would be an irreconcilable contradiction between different cosmological parameters.  The big bang makes certain predictions about things like the hydrogen/helium ratio, the age of stars and galaxies, the temperature of the cosmic microwave background, etc. The observational evidence we have thus far shows that all of these agree with the big bang model.  If, as we refine our observations, these begin to contradict each other, then the big bang would face a problem.

Of course falsifiability isn’t the only thing that makes a model scientific. Scientific models also have to be supported by a confluence of evidence. The big bang has that through galactic redshift, the cosmic microwave background, the distribution and evolution of galaxies in the universe, and lots more.  Like any robust scientific theory, the big bang model (or more properly the ΛCDM model, of which the big bang is a part) is both supported by a wealth of evidence and capable of being overturned by new discoveries.

The point is that science is not confined to the lab. It is a process of gathering and analyzing data to produce models that work.

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Although there is a great deal of evidence for the big bang, it does raise an interesting question.  If the universe began with the big bang, what caused the big bang? That’s a bit of a stumper, because we aren’t entirely sure.  Observationally, we have a good understanding of the universe as far back as nucleosynthesis, which occurred when the universe was about 10 seconds old.  We also have some initial observational evidence of the inflationary period, which occurred in the earliest moments of the universe.    As for the cause of the universe, we just have ideas at this point.  One of the more popular ones is that the universe quite literally came from nothing.

The “nothing” in this case is not the type of nothing we might typically imagine. Here, “nothing” refers to the idea that there are no particles, energy, space, or anything else that could be considered “real” in a traditional sense.  Instead there is only a quantum potential, or a nebulous cosmic wavefunction.  You might argue that a quantum state subject to some set of physical laws is hardly “nothing”, and I’d be inclined to agree with you, but in cosmology the term “nothing” has kind of stuck.  It’s similar to the term “big bang” being used for an event that was neither big nor explosive.

That said, there has been some interesting theoretical work on just what this quantum nothing might have been like.  One such work was recently published in Physical Review D. In this paper the authors looked at what is known as the Wheeler-DeWitt equation, which is a way to describe the entire universe within the framework of quantum mechanics.  The model is not without its problems, but it is a way to study the intersection between general relativity (gravity) and quantum theory.

Within the Wheeler-DeWitt formalism, it is possible for quantum fluctuations to occur.  Basically, within the quantum nothing fluctuations of spacetime can appear, though they would dissolve back into the quantum-ness. The team showed that in certain cases it is possible for such a fluctuation to expand rapidly, where the state of the quantum system acts as a cosmological constant to cause inflation.  Once that occurs, the fluctuation is to big to dissolve back into a quantum state, and has thus become “real”.  What this shows is that it is possible for a quantum state to give rise to a universe with an early inflationary period, similar to the way our universe seemed to arise.

It should be kept in mind that this is still very speculative.  This work is really a demonstration of a possibility, and not confirmation of how our universe came to be.  We are only beginning to gather evidence on the inflationary period of the big bang, and we’ll need a solid understanding of that period before we can explore any quantum origin of the Cosmos.

In the end, these ideas might prove successful, or it may turn out that nothing comes of it.

Paper: Dongshan He, Dongfeng Gao, and Qing-yu Cai. Spontaneous creation of the universe from nothing.  Phys. Rev. D 89, 083510 (2014)

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The origin of the universe is often portrayed in popular science as a vast sea of darkness.  Centered in this darkness is a bright point of light, which suddenly expands, filling your view with light, fading into a dance of galaxies.  Of course this raises all sorts of questions:  What did the universe expand into? What triggered the initial explosion?  Where did all that matter and energy come from? The problem is, this isn’t how cosmologists see the big bang at all.

Popular science loves to portray cosmology starting with the big bang and ending with our modern universe, but in astrophysics we work the other way around.  We start with what we observe in the universe today, and work back as far as we can to the early moments of the universe.  This is an important distinction, because it means we don’t have to know every detail of the origin of the universe to know quite a bit about its history and early period.  In the same way, biologists don’t have to know exactly how early life appeared on Earth (abiogenesis) to know that the variety of life we see today evolved through natural selection from that early common ancestor.  Understanding that earliest moment is our destination, not our starting hypothesis.

So let’s walk through the process of how what we observe today leads us to conclude that the universe started with a big bang 13.8 billion years ago.  It’s a rather detailed process, but I’ve written about many of the underlying topics before.  Instead of restating all of them here, I’ve just summarized them and added links to earlier posts).  How far you want to delve into the details is up to you, but I think it’s useful to explain just how well we understand the origin and history of the universe.

The first clue was found by observing the relation between a galaxy’s distance and speed. There are various ways we can determine the distance of a particular galaxy.  For example, there are certain variable stars known as Cepheid variables that brighten and darken at a rate correlating to their overall brightness.  There is a type of supernova called type Ia that has a pretty standard brightness.  By observing the apparent brightness of these things in a particular galaxy we can get an accurate measurement of just how far away they actually are.

We can measure the speed of a galaxy by observing the Doppler shift of light coming from the galaxy.  Atoms and molecules emit and absorb light at specific wavelengths.  By observing this spectral pattern we can determine what type of atoms and molecules exist in a particular galaxy.  But if a galaxy is moving away from us, that pattern is shifted a bit toward the red end of the spectrum.  The light waves emitted from the galaxy are stretched a bit due to the galaxy’s motion away from us.  Similarly, if a galaxy is moving toward us, the pattern is shifted a bit toward the blue end of the spectrum, as the light waves bunch up a bit.  You’ve probably experienced this effect with sound, where the sound of a passing car or train sounds higher as it approaches you and lower as it passes you by.

When we observe different galaxies, we find that the light of most galaxies are red shifted.  Not only that, the more distant a galaxy is, the more its light tends to be redshifted.  This was first observed in detail by Edwin Hubble in 1927.  Hubble demonstrated that there was a linear relationship between a galaxies distance and its redshift.  When this was first observed, it was generally thought that the universe was pretty static. If that were the case, then one would expect galactic speeds to be random, with some moving toward us, and some moving away from us.  Since galaxies appear to be receding from us at a rate proportional to their distance, a better model is that of an expanding universe.  Not just fixed region of space where galaxies are flying away from us, because that wouldn’t account for more distant galaxies having greater speeds.  Instead it must be that the universe itself must be expanding, kind of like bread dough rising.

That seems like a rather radical idea (which it was), but it is the model that best fits the data.  It also agrees with Einstein’s theory of relativity, which has been verified extensively.  Einstein had actually had a chance to predict the expansion of the universe, since it’s a consequence of the theory of relativity.  But Einstein assumed the universe must be static, so he introduced a cosmological constant to allow for stationary universe.  More modern observations show that not only is the universe expanding, it is expanding at an ever increasing rate, and one way to account for this is through a cosmological constant.

So if the universe is currently expanding, then in the past the universe must have been smaller.  Extrapolating really, really far back, the universe must have been really, really small.  So it must have had a beginning as a small initial “seed”.  This idea was first proposed by Georges Lemaître, who referred to that initial seed as the primordial atom.  From Hubble’s original data you could get an age for this primordial atom of 10 – 20 billion years, which would be the age of the universe.

Now this is a huge leap.  After all, no one looks at a loaf of rising bread and presumes a week ago it must have begun as ultra dense “primordial dough”.  Many astronomers thought extrapolating cosmic expansion back to a primordial atom was pseudoscientific nonsense.  Among them was astronomer Fred Hoyle, who actually coined the term “big bang”.  (It’s rumored that Hoyle meant the term to mock the idea, but Hoyle denied it.)  Hoyle proposed an alternative interpretation, known as the steady-state model.  In Hoyle’s model, the universe has a process of slow continuous creation of matter, which creates the positive pressure necessary to cause cosmic expansion.  Thus the universe is ever expanding, but is ageless.

Of course both of these models have very clear predictions.  In particular, the big bang model predicts a very specific signature.  If the universe began as a dense primordial fireball, then a remnant of that intensely hot period must still exist.  As the universe expanded its temperature would cool, but it wouldn’t be zero.  So either there is a background temperature to the universe, or the big bang model is wrong.  Given Hubble’s observations of cosmic expansion, that temperature should be a few Kelvin today.  In 1965 just such a background temperature was observed by Penzias and Wilson.  This cosmic microwave background as it now known matched the temperature of a thermal blackbody exactly, with a temperature of 2.7 K.

The cosmic microwave background (CMB) and the evidence of cosmic expansion demonstrated pretty clearly that billions of years ago the universe was a primordial fireball.  But we have to be a bit careful here.  The simple existence of the CMB does not tell us the universe began as a primordial atom.  The CMB is not light from the big bang itself, but light from when the universe had a temperature of about 4000 K.  At higher temperatures hydrogen ionizes into a plasma of electrons and protons.  Light is heavily scattered in a plasma, so it isn’t possible for us to see anything further back than then.

Light travels at a finite speed (about 300,000 km/s), and that means the more distant an object is the longer it takes for the light to reach us.  That means when we view distant objects such as galaxies, we are seeing them as they were in the past.  It also means when we observe something that happened in the past, we observe how it happened light years away from us.  Our best measurement of the age of the CMB is 13.798 billion years ago.  That means the CMB we observe is from a region of space that was 13.798 billion light years from our current position at that time.  Due to the expansion of the universe, that region of space is about 47 billion light years from us today.  In other words, by the time the universe had cooled enough to condense into neutral gas (the time of the CMB), that gas covered a region at least  28 billion light years across, because that was the size of the observable universe at the time.

So now that we know that 13.8 billion years ago the observable universe was a primordial fireball 28 billion light years wide, what’s to say we can extrapolate further back than that?  What if the universe simply began as a fiery expanse of gas?  To go beyond the time of the CMB we need high energy physics.

We know high energy physics pretty well.  We’ve been doing high-energy experiments since the mid 20th century, so we have a good understanding of how matter behaves at high energies.  If we use this knowledge to extrapolate before the CMB, we reach a point where the temperature would be about a billion Kelvin, too hot for atomic nuclei to form.  If the universe began at least that hot, then as it cooled the protons would collide with such energy that a fourth of them would fuse into helium nuclei, a process known as nucleosynthesis.  That means the matter of the post CMB universe would have to consist of about 75% hydrogen and 25% helium by mass (with small traces of elements such as lithium).  This ratio agrees perfectly with the distribution of elements we see today.  We have recently observed the spectra of distant quasars and observed early gas clouds that contain no higher elements (carbon, nitrogen, etc), exactly as we would expect from nucleosynthesis.

Once we’ve reached back to nucleosynthesis, we’ve covered the history of the universe back 13.8 billion years to the time where the initial elements of the universe formed.  At this point the universe is at most about 10 seconds old.  We can extrapolate further back using particle physics, to a time when quarks and gluons form into protons and neutrons, or earlier, where the weak nuclear force and electromagnetism unite into the electroweak force. At this point the universe is no more than a trillionth of a second old, and the observable universe is about the size of a grapefruit.

This is what particle physics, astronomy and astrophysics tells us.  This is what we can demonstrate scientifically.  The early observable universe was once small enough to fit in the palm of your hand.

Of course this is only the observable universe.  Remember that our view is limited by the finite age of the universe.  If that early universe were truly only the size of a grapefruit, then its mass and energy would have curved space over time, and we would see the effects of that curvature on the expansion of the universe.  But to the limits of our measurements the universe has no overall curvature.  That means the universe must be much larger than the region we can observe.  As best we can tell, the universe is infinite in size. So our best understanding of the universe is that it’s infinite in space, finite in time, made of matter, dark matter and dark energy.

And we are a part of it all.

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