Posted on by Vanessa Janek

Cosmology 101: The End

A1689-zD1, one of the brightest and most distant galaxies, is 12.8 billion light years away - an extremely far distance in our expanding universe. Image credit: NASA/ESA/JPL-Caltech/STScI

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Welcome back to the third, and last, installment of Cosmology 101. So far, we’ve covered the history of the universe up to the present moment. But what happens next? How will our universe end? And how can we be so sure that this is how the story unfolded?

Robert Frost once wrote, “Some say the world will end in fire; some say in ice.” Likewise, some scientists have postulated that the universe could die either a dramatic, cataclysmic death – either a “Big Rip” or a “Big Crunch” – or a slower, more gradual “Big Freeze.” The ultimate fate of our cosmos has a lot to do with its shape. If the universe were open, like a saddle, and the energy density of dark energy increased without bound, the expansion rate of the cosmos would eventually become so great that even atoms would be torn apart – a Big Rip. Conversely, if the universe were closed, like a sphere, and gravity’s strength trumped the influence of dark energy, the outward expansion of the cosmos would eventually come to a halt and reverse, collapsing on itself in a Big Crunch.

Despite the poetic beauty of fire, however, current observations favor an icy end to our universe – a Big Freeze. Scientists believe that we live in a spatially flat universe whose expansion is accelerating due to the presence of dark energy; however, the total energy density of the cosmos is most likely less than or equal to the so-called “critical density,” so there will be no Big Rip. Instead, the contents of the universe will eventually drift prohibitively far away from each other and heat and energy exchange will cease. The cosmos will have reached a state of maximum entropy, and no life will be able to survive. Depressing and a bit anti-climactic? Perhaps. But it probably won’t be perceptible until the universe is at least twice its current age.

At this point you might be screaming, “How do we know all this? Isn’t it all just rampant speculation?” Well, first of all, we know without a doubt that the universe is expanding. Astronomical observations consistently demonstrate that light from distant stars is always redshifted relative to us; that is, its wavelength has been stretched due to the expansion of the cosmos. This leads to two possibilities when you wind back the clock: either the expanding universe has always existed and is infinite in age, or it began expanding from a smaller version of itself at a specific time in the past and thus has a fixed age. For a long time, proponents of the Steady State Theory endorsed the former explanation. It wasn’t until Arno Penzias and Robert Wilson discovered the cosmic microwave background in 1965 that the big bang theory became the most accepted explanation for the origin of the universe.

Why? Something as large as our cosmos takes quite a while to cool completely. If the universe did, in fact, began with the kind of blistering energies that the big bang theory predicts, astronomers should still see some leftover heat today. And they do: a uniform 3K glow evenly dispersed at every point in the sky. Not only that – but WMAP and other satellites have observed tiny inhomogeneities in the CMB that precisely match the initial spectrum of quantum fluctuations predicted by the big bang theory.

What else? Take a look at the relative abundances of light elements in the universe. Remember that during the first few minutes of the cosmos’ young life, the ambient temperature was high enough for nuclear fusion to occur. The laws of thermodynamics and the relative density of baryons (i.e. protons and neutrons) together determine exactly how much deuterium (heavy hydrogen), helium and lithium could be formed at this time. As it turns out, there is far more helium (25%!) in our current universe than could be created by nucleosynthesis in the center of stars. Meanwhile, a hot early universe – like the one postulated by the big bang theory – gives rise to the exact proportions of light elements that scientists observe in the universe today.

But wait, there’s more. The distribution of large-scale structure in the universe can be mapped extremely well based solely on observed anisotropies in the CMB. Moreover, today’s large-scale structure looks very different from that at high redshift, implying a dynamic and evolving universe. Additionally, the age of the oldest stars appears to be consistent with the age of the cosmos given by the big bang theory. Like any theory, it has its weaknesses – for instance, the horizon problem or the flatness problem or the problems of dark energy and dark matter; but overall, astronomical observations match the predictions of the big bang theory far more closely than any rival idea. Until that changes, it seems as though the big bang theory is here to stay.

Posted on by Vanessa Janek

Cosmology 101: The Present

A map of the CMB as captured by the Wilkinson Microwave Anisotropy Probe. Credit: WMAP team
A map of the Cosmic Microwave Background (CMB) as captured by the Wilkinson Microwave Anisotropy Probe. Credit: WMAP team

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Welcome back! Last time, we discussed the first few controversial and eventful moments following the birth of our cosmos. Looking around us today, we know that in the span of just a few billion years, the universe was transformed from that blistering amalgam of tiny elementary particles into a vast and organized expanse just teeming with large-scale structure. How does something like that happen?

Let’s recap. When we left off, the universe was a chaotic soup of simple matter and radiation. A photon couldn’t travel very far without bumping into and being absorbed by a charged particle, exciting it and later being emitted, just to go through the cycle again. After about three minutes, the ambient temperature had cooled to such an extent that these charged particles (protons and electrons) could begin to come together and form stable nuclei.

But, despite the falling temperature, it was still hot enough for these nuclei to start to combine into heavier elements. For the next few minutes, the universe cooked up various isotopes of hydrogen, helium and lithium nuclei in a process commonly known as big bang nucleosynthesis. As time went on and the universe expanded even further, these nuclei slowly captured surrounding electrons until neutral atoms dominated the landscape. Finally, after about 300,000 years, photons could travel freely across the universe without charged particles getting in their way. The cosmic microwave background radiation that astronomers observe today is actually the relic light from that very moment, stretched over time due to the expansion of the universe.

If you look at a picture of the CMB (above), you will see a pattern of differently colored patches that represent anisotropies in the background temperature of the cosmos. These temperature differences originally stemmed from tiny quantum fluctuations that were dramatically blown up in the very early universe. Over the next few hundred million years, the slightly overdense regions in the spacetime fabric attracted more and more matter (both baryonic – the kind that you and I are made of – and dark) under the influence of gravity. Some small regions eventually became so hot and dense that they were able to begin nuclear fusion in their cores; thus, in a delicate dance between external gravity and internal pressure, the first stars were born. Gravity then continued its pull, dragging clumps of stars into galaxies and later, clumps of galaxies into galaxy clusters. Some massive stars collapsed into black holes. Others grew so heavy and bloated that they exploded, spewing chunks of metal-rich debris in every direction. About 4.7 billion years ago, some of this material found its way into orbit around one unassuming main sequence star, creating planets of all sizes, shapes, and compositions – our Solar System!

Billions of years of geology and evolution later, here we are. And there the rest of the universe is. It’s a pretty striking story. But what’s next? And how do we know that all of this theory is even close to correct? Make sure to come back next time to find out!

Posted on by Vanessa Janek

Cosmology 101: The Beginning

Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that followed. Credit: NASA/WMAP Science Team.
Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that followed. Credit: NASA/WMAP Science Team.

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Editor’s note: The article “The Universe Could be 250 Times Bigger Than What is Observable” sparked a sizable discussion among our readers, with several suggesting UT should have a series of articles about cosmology — a Cosmology 101, if you will. Our newest writer, Vanessa D’Amico, who wrote the aforementioned article, begins the Cosmology 101 series today, starting at the very beginning.

How did the universe get its start? It’s one of the most pressing questions in cosmology, and likely one that will be around for a while. Here, I’ll begin by explaining what scientists think they know about the first formative seconds of the universe’s life. More than likely, the story isn’t quite what you might think.

In the beginning, there was… well, we don’t really know. One of the most prevalent misconceptions in cosmology is that the universe began as an immensely small, inconceivably dense collection of material that suddenly exploded, giving rise to space as we know it. There are a number of problems with this idea, not least of all the assumption implicit in an event termed the big “bang.” In truth, nothing “banged.” The notion of an explosion brings to mind an expanding tide of material, gradually filling the space around it; however, when our universe was born, there was no space. There was no time either. There was no vacuum. There was literally nothing.

Then the universe was born. Extremely high energies during the first 10-43 seconds of its life make it very difficult for scientists to determine anything conclusive about the origin of the cosmos. Of course, if cosmologists are correct about what they believe may have happened next, it doesn’t much matter. According to the theory of inflation, at about 10-36 seconds, the universe underwent a period of exponential expansion. In a matter of a few thousandths of a second, space inflated by a factor of about 1078, quickly separating what were once adjoining regions by unfathomable distances and blowing up tiny quantum fluctuations in the fabric of spacetime.

Inflation is an appealing theory for a number of reasons. First of all, it explains why we observe the universe to be homogeneous and isotropic on large scales – that is, it looks the same in all directions and to all observers. It also explains why the universe visually appears to be flat, rather than curved. Without inflation, a flat universe requires an extremely fine-tuned set of initial conditions; however, inflation turns this fine-tuning into a trick of scale. A familiar analogy: the ground under our feet appears to be flat (even though we know we live on a spherical planet) because we humans are so much smaller than the Earth. Likewise, the inflated universe is so enormous compared to our local field of view that it appears to be spatially flat.

As the theory goes, the end of inflation gave way to a universe that looked slightly more like the one we observe today. The vacuum energy that drove inflation suddenly transformed into a different kind of energy – the kind that could create elementary particles. At this point (only 10-32 seconds after the birth of the universe), the ambient temperature was still far too hot to build atoms or molecules from these particles; but as the seconds wore on, space expanded and cooled to the point where quarks could come together and form protons and neutrons. High-energy photons continued to dart around, continually striking and exciting charged protons and electrons.

So what happened next? How did this chaotic soup of matter and radiation become the vast expanse of organized structure that we see today? What’s going to happen to the universe in the future? And how do we know that this is the way the story unfolded? Make sure to check out the next few installments of Cosmology 101 for the answers to these questions and more!

Posted on by Matt Williams

What Is A Singularity?

Artist's conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library
Artist's conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library

Ever since scientists first discovered the existence of black holes in our universe, we have all wondered: what could possibly exist beyond the veil of that terrible void? In addition, ever since the theory of General Relativity was first proposed, scientists have been forced to wonder, what could have existed before the birth of the Universe – i.e. before the Big Bang?

Interestingly enough, these two questions have come to be resolved (after a fashion) with the theoretical existence of something known as a Gravitational Singularity – a point in space-time where the laws of physics as we know them break down. And while there remain challenges and unresolved issues about this theory, many scientists believe that beneath veil of an event horizon, and at the beginning of the Universe, this was what existed.

Definition:

In scientific terms, a gravitational singularity (or space-time singularity) is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system. In other words, it is a point in which all physical laws are indistinguishable from one another, where space and time are no longer interrelated realities, but merge indistinguishably and cease to have any independent meaning.

Credit: ESA/Hubble, ESO, M. Kornmesser
This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. Credit: ESA/Hubble, ESO, M. Kornmesse

Origin of Theory:

Singularities were first predicated as a result of Einstein’s Theory of General Relativity, which resulted in the theoretical existence of black holes. In essence, the theory predicted that any star reaching beyond a certain point in its mass (aka. the Schwarzschild Radius) would exert a gravitational force so intense that it would collapse.

At this point, nothing would be capable of escaping its surface, including light. This is due to the fact the gravitational force would exceed the speed of light in vacuum – 299,792,458 meters per second (1,079,252,848.8 km/h; 670,616,629 mph).

This phenomena is known as the Chandrasekhar Limit, named after the Indian astrophysicist Subrahmanyan Chandrasekhar, who proposed it in 1930. At present, the accepted value of this limit is believed to be 1.39 Solar Masses (i.e. 1.39 times the mass of our Sun), which works out to a whopping 2.765 x 1030 kg (or 2,765 trillion trillion metric tons).

Another aspect of modern General Relativity is that at the time of the Big Bang (i.e. the initial state of the Universe) was a singularity. Roger Penrose and Stephen Hawking both developed theories that attempted to answer how gravitation could produce singularities, which eventually merged together to be known as the Penrose–Hawking Singularity Theorems.

Illustration of the Big Bang Theory
The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com

According to the Penrose Singularity Theorem, which he proposed in 1965, a time-like singularity will occur within a black hole whenever matter reaches certain energy conditions. At this point, the curvature of space-time within the black hole becomes infinite, thus turning it into a trapped surface where time ceases to function.

The Hawking Singularity Theorem added to this by stating that a space-like singularity can occur when matter is forcibly compressed to a point, causing the rules that govern matter to break down. Hawking traced this back in time to the Big Bang, which he claimed was a point of infinite density. However, Hawking later revised this to claim that general relativity breaks down at times prior to the Big Bang, and hence no singularity could be predicted by it.

Some more recent proposals also suggest that the Universe did not begin as a singularity. These includes theories like Loop Quantum Gravity, which attempts to unify the laws of quantum physics with gravity. This theory states that, due to quantum gravity effects, there is a minimum distance beyond which gravity no longer continues to increase, or that interpenetrating particle waves mask gravitational effects that would be felt at a distance.

Types of Singularities:

The two most important types of space-time singularities are known as Curvature Singularities and Conical Singularities. Singularities can also be divided according to whether they are covered by an event horizon or not. In the case of the former, you have the Curvature and Conical; whereas in the latter, you have what are known as Naked Singularities.

A Curvature Singularity is best exemplified by a black hole. At the center of a black hole, space-time becomes a one-dimensional point which contains a huge mass. As a result, gravity become infinite and space-time curves infinitely, and the laws of physics as we know them cease to function.

Conical singularities occur when there is a point where the limit of every general covariance quantity is finite. In this case, space-time looks like a cone around this point, where the singularity is located at the tip of the cone. An example of such a conical singularity is a cosmic string, a type of hypothetical one-dimensional point that is believed to have formed during the early Universe.

And, as mentioned, there is the Naked Singularity, a type of singularity which is not hidden behind an event horizon. These were first discovered in 1991 by Shapiro and Teukolsky using computer simulations of a rotating plane of dust that indicated that General Relativity might allow for “naked” singularities.

In this case, what actually transpires within a black hole (i.e. its singularity) would be visible. Such a singularity would theoretically be what existed prior to the Big Bang. The key word here is theoretical, as it remains a mystery what these objects would look like.

For the moment, singularities and what actually lies beneath the veil of a black hole remains a mystery. As time goes on, it is hoped that astronomers will be able to study black holes in greater detail. It is also hoped that in the coming decades, scientists will find a way to merge the principles of quantum mechanics with gravity, and that this will shed further light on how this mysterious force operates.

We have many interesting articles about gravitational singularities here at Universe Today. Here is 10 Interesting Facts About Black Holes, What Would A Black Hole Look Like?, Was the Big Bang Just a Black Hole?, Goodbye Big Bang, Hello Black Hole?, Who is Stephen Hawking?, and What’s on the Other Side of a Black Hole?

If you’d like more info on singularity, check out these articles from NASA and Physlink.

Astronomy Cast has some relevant episodes on the subject. Here’s Episode 6: More Evidence for the Big Bang, and Episode 18: Black Holes Big and Small and Episode 21: Black Hole Questions Answered.

Sources:

Posted on by Mark Thompson

Planck Unveils the Wonders of the Universe

Six areas of the sky in which distant galaxies can be seen by Planck, overlaid on the Planck’s first all-sky image. The emission from our own Galaxy, seen in blue and white, has to be removed before the distant population of galaxies can be seen. Each square inset image is around the same size as the Full Moon. Image credit: ESA / Planck Collaboration.

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The mission began on 13th August 2009 with a goal to image the echo’s of the birth of the Universe, the cosmic background radiation. But scientists working on the European Space Agency’s (ESA) Planck mission got more than they bargained for making ground breaking discoveries and shedding light on old mysteries. By studying light from the far reaches of the Universe, Planck has to look through the rest of the Universe first and it was during this, that the incredible discoveries were made.

The crazy thing about looking at the far reaches of the Universe is that we actually look back in time as it takes billions of years for the light to reach us here on Earth. This enables astronomers to look back in time and study the evolution of the Universe almost back to the Big Bang itself. Amongst the discoveries was evidence for an otherwise invisible population of galaxies that seem to be shrouded in dust billions of years in the past. Star formation rates in these galaxies seem to be happening at an incredible pace, some 10-1000 times higher than we see in our own Milky Way galaxy today. Joanna Dunkley, of Oxford University, said “Planck’s measurements of these distant galaxies are shedding new light on when and where ancient stars formed in the early universe”.

One of the challenges of getting a clear view of these galaxies though has been removing the so called ‘anomalous microwave emission’ (AME) foreground haze. This annoying and poorly understood interference, which is thought to originate in our own Galaxy, has only just been pierced through with Planck’s instruments. But in doing so, clues to its nature have been unveiled. It seems that the AME is coming from dust grains in our Galaxy spinning several tens of billions of times per second, perhaps from collisions with incoming faster-moving atoms or from ultra-violet radiation. Planck was able to ‘remove’ the foreground microwave haze, leaving the distant galaxies in perfect view and the cosmic background radiation untouched.

Its also the ideal instrument to detect very cold matter in the form of dust in our Galaxy and beyond, thanks to its broad wavelength coverage. During its study, it detected over 900 clumps of cold dark dust clouds which are thought to represent the first stages of star birth. By studying a number of nearby galaxies within a few billion light years, the study shows that some of them contain much more cold dust than previously thought. Dr David Clements from Imperial College London says “Planck will help us to build a ladder connecting our Milky Way to the faint, distant galaxies and uncovering the evolution of dusty, star forming galaxies throughout cosmic history.”

These results make Planck a roaring success but it doesn’t stop there. Other results just published include data on galaxy clusters revealing them silhouetted against the cosmic microwave background. These clusters contain thousands of individual galaxies gravitational bound together into gigantic strings and loops.

The Planck mission, which was in development for 15 years is already providing some ground breaking science in its first few years of operation and its exciting to wonder what we will see from it in the years that lie ahead.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Posted on by Steve Nerlich

Astronomy Without A Telescope – Home Made Quark-Gluon Soup

The most powerful operational heavy-ion collider in the world, the Relativistic Heavy Ion Collider (RHIC) recently recorded the highest ever temperature created in an Earth-based laboratory of 4 trillion Kelvin. Achieved at the almost speed of light collision of gold ions, this resulted in the temporary existence of quark-gluon soup – something first seen at about ten to the power of minus twelve of the first second after the big bang.

And sure, the Large Hadron Collider (LHC) may one day soon be the most powerful heavy-ion collider in the world (although it will spend most of its time investigating proton to proton collisions). And sure, maybe it’s going to generate a spectacular 574 TeV when it collides its first lead ions. But you have to win the game before you get the trophy.

To give credit where it’s due, the LHC is already the most powerful particle collider in the world – having achieved proton collision energies of 2.36 TeV in late 2009. And it should eventually achieve proton collision energies of 14 TeV, but that will come well after its scheduled maintenance shutdown in 2012, ahead of achieving its full design capabilities from 2013. It has already circulated a beam of lead ions – but we are yet to see an LHC heavy ion collision take place.

So, for the moment it’s still RHIC putting out all the fun stuff. In early March 2010, it produced the largest ever negatively charged nucleus – which is anti-matter, since you can only build matter nuclei from protons and/or neutrons which will only ever have a positive or a neutral charge.

This antimatter nucleus carried an anti-strange quark – which is crying out for a new name… mundane quark, conventional quark? And since the only matter nuclei containing strange quarks are hypernuclei, RHIC in fact created an antihypernucleus. Wonderful.

Then there’s the whole quark-gluon soup story. Early experiments at RHIC reveal that this superhot plasma behaves like a liquid with a very low viscosity— and may be what the universe was made of in its very early moments.  There was some expectation that melted protons and neutrons would be so hot that surely you would get a gas – but like the early universe, with everything condensed into a tiny volume, you get a super-heated liquid (i.e. soup).

An aerial view of the Relativistic Heavy Ion Collider (RHIC) in Upton, NY. The Alternating Gradient Synchrotron (AGS) built in the 1960s now works as a pre-accelerating injector for the larger RHIC.

The LHC hopes to deliver the Higgs, maybe a dark matter particle and certainly anti-matter and micro black holes by the nano-spoonful. And after that, there’s talk of building the Very Large Hadron Collider, which promises to be bigger, more powerful and more expensive.

But if that project doesn’t fly, we can still ramp up the existing colliders. Ramping up a particle collider is an issue of luminosity, where the desired outcome is a more concentrated and focused particle beam – with an increased energy density achieved by cramming more particles into a cross section of the beam you are sending around the particle accelerator. Both RHIC and the LHC have plans to undertake an upgrade to achieve an increase of their respective luminosities by up to a factor of 10. If successful, we can look forward to RHIC II and the Super Large Hadron Collider coming online sometime after 2020. Fun.

Posted on by Jean Tate

Big Bang Timeline

A fraction of a second after the big bang, the universe underwent inflation - but what does that mean? credit: NASA/WMAP
Time line of the Universe (Credit: NASA/WMAP Science Team)

The Big Bang timeline is basically just a list of relative times at which the major events in the history of the universe occurred, per the collection of theories, models, and hypotheses which together form what is called the Big Bang theory.

The start – when time began, when t = 0 – is not actually part of the Big Bang timeline (!), contrary to popular belief. That’s because the two theories of physics which are at the heart of the Big Bang theory – General Relativity (GR) and the Standard Model (of particle physics; SM for short) – are mutually incompatible, and that incompatibility becomes so intolerable that saying anything about what happened in the first Planck second (approx 10-43 second) is meaningless.

In fact, the closer to the Planck regime – when GR and the SM are utterly incompatible – the less reliable are our descriptions … but the relative times are nonetheless pretty good.

Actually, that’s not quite true … what is relatively certain are temperatures; forces, matter, and radiation interact in very distinct ways, depending on the temperature (and pressure, or density), but converting from temperature back to time depends on various parameters which are not so well pinned down. However, once the average mass-energy density of the universe, today, is estimated, the clock can be wound back with some confidence (it’s ~six hydrogen atoms per cubic meter, or about 7 x 10-27 kg/m3).

Around 10-35 seconds leptons and baryons were created (the strong force became a distinct force), and inflation caused the universe to expand so much that the part which later became our observable universe was both flat (no curvature, in the GR sense) and incredibly smooth (with only tiny variations in density due to quantum effects).

At around 10-11 seconds the electromagnetic and weak force became distinct.

And by about a microsecond the universe underwent another phase change … it was no longer a quark-gluon plasma, but hadrons formed (protons and neutrons).

When t = 1 second (more or less), nuclear reactions produced light nuclides, such as deuterium and helium-3 (before this time the universe was too hot for them to form) – Big Bang nucleosynthesis.

The earliest part of the universe we can still see, directly, happened when the electrons and protons (and other nuclei) combined to form hydrogen atoms; this is the recombination era, and we see it today as the cosmic microwave background … and gravity took over as the dominant force (before this it was electromagnetism – the universe was ‘radiation dominated’ – and before that, at the time of nucleosynthesis, the strong and weak forces ruled).

The rest, as they say, is history … the Dark Ages (during which the first stars were formed), the era of recombination (when stars and quasars ionized the diffuse hydrogen), galaxy formation, … and then about 13.4 billion years later we observed the skies and worked out the timeline!

There’s a lot of good material on the web on the Big Bang timeline; here are some: John Baez (who’s always worth reading) has a brief timeline, in terms of temperature; there’s a more extensive one from the University of Wisconsin-Madison, and perhaps the best, A Brief History of the Universe (University of Cambridge).

Want to explore more? Here are some of the many Universe Today articles on the Big Bang timeline: Cosmologists Look Back to Cosmic Dawn, A Star as Old as the Universe, and Book Review: The Mystery of the Mission Antimatter.

Astronomy Cast has several episodes for you to explore, to learn more about the Big Bang timeline; here are a few: The Big Bang and Cosmic Microwave Background, Inflation, and this 2009 Questions Show.

Sources:
http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang
http://www.damtp.cam.ac.uk/research/gr/public/bb_history.html

Posted on by John Carl Villanueva

What is the Oscillating Universe Theory?

The Oscillating Universe Theory is a cosmological model that combines both the Big Bang and the Big Crunch as part of a cyclical event. That is, if this theory holds true, then the Universe in which we live in exists between a Big Bang and a Big Crunch.

In other words, our universe can be the first of a possible series of universes or it can be the nth universe in the series.

As we know, in the Big Bang Theory, the Universe is believed to be expanding from a very hot, very dense, and very small entity. In fact, if we extrapolate back to the moment of the Big Bang, we are able to reach a point of singularity characterized by infinitely high energy and density, as well as zero volume.

This description would only mean one thing – all the laws of physics will be thrown out of the window. This is understandably unacceptable to physicists. To make matters worse, some cosmologists even believe that the Universe will eventually reach a maximum point of expansion and that once this happens, it will then collapse into itself.

This will essentially lead to the same conditions as when we extrapolate back to the moment of the Big Bang. To remedy this dilemma, some scientists are proposing that perhaps the Universe will not reach the point of singularity after all.

Instead, because of repulsive forces brought about by quantum effects of gravity, the Universe will bounce back to an expanding one. An expansion (Big Bang) following a collapse (Big Crunch) such as this is aptly called a Big Bounce. The bounce marks the end of the previous universe and the beginning of the next.

The probability of a Big Bounce, or even a Big Crunch for that matter, is however becoming negligible. The most recent measurements of the CMBR or cosmic microwave background radiation shows that the Universe will continue on expanding and will most likely end in what is known as a Big Freeze or Heat Death.

CMBR readings are currently being gathered by a very accurate measuring device known as the WMAP or Wilkinson Microwave Anisotropy Probe. It is the same device that has measured with sharp precision the age of our universe. It is therefore highly unlikely that future findings will deviate largely from what has been discovered regarding the Universe’s expansion now.

There is however one mysterious entity whose deeper understanding of may change the possibilities. This entity, known as dark energy, is believed to be responsible for pushing the galaxies farther apart and subsequently the universe’s accelerated expansion. Unless its actual properties are very dissimilar from what it is showing now, we may have to shelve the Oscillating Universe Theory.

We’ve got a few articles that touch on the Oscillating Universe Theory here in Universe Today. Here are two of them:

Physics World also has some more:

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

Sources:
PBS.org
Wikipedia

Posted on by John Carl Villanueva

The Big Crunch: The End of Our Universe?

The Big Crunch is one of the scenarios predicted by scientists in which the Universe may end. Just like many others, it is based on Einstein’s Theory of General Relativity. That is, if the Big Bang describes how the Universe most possibly began, the Big Crunch describes how it will end as a consequence of that beginning.

It tells us that the Universe’s expansion, which is due to the Big Bang, will not continue forever. Instead, at a certain point in time, it will stop expanding and collapse into itself, pulling everything with it until it eventually turns into the biggest black hole ever. Well, we all know how everything is squeezed when in that hole. Hence the name Big Crunch.

For scientists to predict with certainty the possibility of a Big Crunch, they will have to determine certain properties of the Universe. One of them is its density. It is believed that if the density is larger than a certain value, known as the critical density, an eventual collapse is highly possible.

You see, initially, scientists believed that there were only two factors that greatly influenced this expansion: the gravitational force of attraction between all the galaxies (which is proportional to the density) and their outward momentum due to the Big Bang.

Now, just like any body that goes against gravity, e.g. when you throw something up, that body will eventually give in and come back down for as long as there is no other force pushing it up.

Thus, that the gravitational forces will win in the end, once seemed like a logical prediction. But that was until scientists discovered that the Universe was actually increasing its rate of expansion at regions farthest from us.

To explain this phenomena, scientists had to assume the presence of an unknown entity, which they dubbed ‘dark energy’. It is widely believed that this entity is pushing all galaxies farther apart. With dark energy, and what little is known about it, in the picture, there seems to be little room for the possibility of a Big Crunch.

Right now, measurements made by NASA’s Chandra X-ray observatory indicate that the strength of dark energy in the University is constant. Just for added information, an increasing dark energy strength would have supported the possibility of a Big Rip, another universe ending that predicted everything (including atoms) to be ripped apart.

Even with an unchanging dark energy strength, an ever expanding universe is still the most likely scenario. So unless data that contradicts these properties are collected, the Big Crunch will have to remain as a less favored theory.

Articles on the big crunch are so hot. It’s a good thing we’ve got a nice collection of them here in Universe Today. Here are two of them:

Here are links from NASA about the big crunch:

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

Sources:
NASA
Wikipedia

Posted on by John Carl Villanueva

Center of the Universe

Where is the center of the Universe? One of the confusing aspects of the whole Big Bang idea is the notion that the Universe doesn’t have a center. You see, if we associate the Big Bang with just about any typical explosion, then we can be tempted to pinpoint the source of the explosion to be the center.

For example, if a firecracker explodes and we take a snapshot of it, then the outermost debris would mark the boundaries of the whole explosion. Looking at the directions of each debris, whether outermost or not, would give us an idea as to where the explosion first started and, subsequently, the center.

Furthermore, if there was a point of origin (the center) of the Big Bang similar to typical explosions, then that point and all regions near it would be comparatively warmer than all others. That is, as you move further from the center of a typical explosion, you would expect to measure cooler temperatures.

However, when scientists point their detectors to all directions, the readings they obtain indicate that the Universe, in general, is homogeneous. No large region is relatively warmer than the rest. Of course, each star is hotter than the regions away from it.

But if we look at many galaxies, and thus including the stars that comprise them, a homogeneous overall picture is painted. If that were so, then that center or point of origin of the explosion cannot exist.

The favorite analogy used by lecturers to simplify the concept of a universe having no center is that of the behavior of dots on the surface of an expanding balloon; for as we know, the Universe is expanding. If we imagine the dots to be galaxies, we can visualize the Universe’s expansion by observing how the dots are brought away from one another as air is slowly blown into the balloon.

For us to get a near accurate analogy, it is important that the observation be limited to the surface alone. If we try to interpret the expansion as being manifested by the whole balloon, we will be tempted into interpreting the geometric center of the balloon as the center of the expanding Universe.

Going back, if we just focus on the surface, you’ll notice that each and every dot will drift farther away from adjacent ones and that no single dot will appear as the center. Also, if you picture yourself as an ant at the center of a single dot, all the other dots will move away from you as if you were the center, just like in our universe.

We’ve got a few articles that touch on the center of the universe here in Universe Today. Here are two of them:

NASA also has some more:

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

Source: NASA Spitzer