Big Bang Archives

March 24, 2014December 23, 2015 by Jason Major

Cosmologists Cast Doubt on Inflation Evidence

Some physicists still have questions on the true origin of the BICEP2 findings...

It was just a week ago that the news blew through the scientific world like a storm: researchers from the BICEP2 project at the South Pole Telescope had detected unambiguous evidence of primordial gravitational waves in the cosmic microwave background, the residual rippling of space and time created by the sudden inflation of the Universe less than a billionth of a billionth of a second after the Big Bang. With whispers of Nobel nominations quickly rising in the science news wings, the team’s findings were hailed as the best direct evidence yet of cosmic inflation, possibly even supporting the existence of a multitude of other universes besides our own.

That is, if they really do indicate what they appear to. Some theorists are advising that we “put the champagne back in the fridge”… at least for now.

Theoretical physicists and cosmologists James Dent, Lawrence Krauss, and Harsh Mathur have submitted a brief paper (arXiv:1403.5166 [astro-ph.CO]) stating that, while groundbreaking, the BICEP2 Collaboration findings have yet to rule out all possible non-inflation sources of the observed B-mode polarization patterns and the “surprisingly large value of r, the ratio of power in tensor modes to scalar density perturbations.”

“However, while there is little doubt that inflation at the Grand Unified Scale is the best motivated source of such primordial waves, it is important to demonstrate that other possible sources cannot account for the current BICEP2 data before definitely claiming Inflation has been proved. “

– Dent, Krauss, and Mathur (arXiv:1403.5166 [astro-ph.CO])

The history of the universe starting the with the Big Bang. Image credit: grandunificationtheory.com

Inflation may very well be the cause — and Dent and company state right off the bat that “there is little doubt that inflation at the Grand Unified Scale is the best motivated source of such primordial waves” — but there’s also a possibility, however remote, that some other, later cosmic event is responsible for at least some if not all of the BICEP2 measurements. (Hence the name of the paper: “Killing the Straw Man: Does BICEP Prove Inflation?”)

Not intending to entirely rain out the celebration, Dent, Krauss, and Mathur do laud the BICEP2 findings as invaluable to physics, stating that they “will be very important for constraining physics beyond the standard model, whether or not inflation is responsible for the entire BICEP2 signal, even though existing data from cosmology is strongly suggestive that it does.”

Now I’m no physicist, cosmologist, or astronomer. Actually I barely passed high school algebra (and I have the transcripts to prove it) so if you want to get into the finer details of this particular argument I invite you to read the team’s paper for yourself here and check out a complementary article on The Physics arXiv Blog.

And so, for better or worse (just kidding — it’s definitely better) this is how science works and how science is supposed to work. A claim is presented, and, regardless of how attractive its implications may be, it must stand up to any other possibilities before deemed the decisive winner. It’s not a popularity contest, it’s not a beauty contest, and it’s not up for vote. What it is up for is scrutiny, and this is just an example of scientists behaving as they should.

Still, I’d keep that champagne nicely chilled.

Source: The Physics arXiv Blog

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Want to read more about the BICEP2 findings from actual physicists? Read more in an article by Peter Coles, see what Matthew Francis has to say in his article on arstechnica here, and watch a video by Sean Carroll on PBS News Hour.

March 17, 2014April 26, 2016 by Brian Koberlein

We’ve Discovered Inflation! Now What?

Polarization patterns imprinted in the CMB. Image Credit: CfA

Days like these make being an astrophysicist interesting. On the one hand, there is the annoucement of BICEP2 that the long-suspected theory of an inflationary big bang is actually true. It’s the type of discovery that makes you want to grab random people off the street and tell them what an amazing thing the Universe is. On the other hand, this is exactly the type of moment when we should be calm, and push back on the claims made by one research team. So let’s take a deep breath and look at what we know, and what we don’t.

Multiverse Theory — Inflation could mean our Universe is just one of many. Credit: Florida State University

First off, let’s dispel a few rumors. This latest research is not the first evidence of gravitational waves. The first indirect evidence for gravitational waves was found in the orbital decay of a binary pulsar by Russell Hulse and Joseph Taylor, for which they were awarded the Nobel prize in 1993. This new work is also not the first discovery of polarization within the cosmic microwave background, or even the first observation of B-mode polarization. This new work is exciting because it finds evidence of a specific form of B-mode polarization due to primordial gravitational waves. The type of gravitational waves that would only be caused by inflation during the earliest moments of the Universe.

It should also be noted that this new work hasn’t yet been peer reviewed. It will be, and it will most likely pass muster, but until it does we should be a bit cautious about the results. Even then these results will need to be verified by other experiments. For example, data from the Planck space telescope should be able to confirm these results assuming they’re valid.

That said, these new results are really, really interesting.

What the team did was to analyze what is known as B-mode polarization within the cosmic microwave background (CMB). Light waves oscillate perpendicular to their direction of motion, similar to the way water waves oscillate up and down while they travel along the surface of water. This means light can have an orientation. For light from the CMB, this orientation has two modes, known as E and B. The E-mode polarization is caused by temperature fluctuations in the CMB, and was first observed in 2002 by the DASI interferometer.

The B-mode polarization can occur in two ways. The first way is due to gravitational lensing. The first is due to gravitational lensing of the E-mode. The cosmic microwave background we see today has travelled for more than 13 billion years before reaching us. Along its journey some of it has passed close enough to galaxies and the like to be gravitationally lensed. This gravitational lensing twists the polarization a bit, giving some of it a B-mode polarization. This type was first observed in July of 2013. The second way is due to gravitational waves from the early inflationary period of the universe. As inflationary period occurred, then it produced gravitational waves on a cosmic scale. Just as the gravitational lensing produces B-mode polarization, these primordial gravitational waves produce a B-mode effect. The discovery of primordial wave B-mode polarization is what was announced today.

The effect of early inflation on the size of the universe. Credit: NASA/COBE

Inflation has been proposed as a reason for why the cosmic microwave background is as uniform as it is. We see small fluctuations in the CMB, but not large hot or cold spots. This means the early Universe must have been small enough for temperatures to even out. But the CMB is so uniform that the observable universe must have been much smaller than predicted by the big bang. However, if the Universe experienced a rapid increase in size during its early moments, then everything would work out. The only problem was we didn’t have any direct evidence of inflation.

Assuming these new results hold up, now we do. Not only that, we know that inflation was stronger than we anticipated. The strength of the gravitational waves is measured in a value known as r, where larger is stronger. It was found that r = 0.2, which is much higher than anticipated. Based upon earlier results from the Planck telescope, it was expected that r < 0.11. So there seems to be a bit of tension with earlier findings. There are ways in which this tension can be resolved, but just how is yet to be determined.

So this work still needs to be peer reviewed, and it needs to be confirmed by other experiments, and then the tension between this result and earlier results needs to be resolved. There is still much to do before we really understand inflation. But overall this is really big news, possibly even Nobel prize worthy. The results are so strong that it seems pretty clear we have direct evidence of cosmic inflation, which is a huge step forward. Before today we only had physical evidence back to when the universe was about a second old, at a time when nucleosynthesis occurred. With this new result we are now able to probe the Universe when it was less than 10 trillion trillion trillionths of a second old.

Which is pretty amazing when you think about it.

March 17, 2014April 26, 2016 by Shannon Hall

Landmark Discovery: New Results Provide Direct Evidence for Cosmic Inflation

The BICEP telescope located at the south pole. Image Credit: CfA / Harvard

Astronomers have announced Nobel Prize-worthy evidence of primordial gravitational waves — ripples in the fabric of spacetime — providing the first direct evidence the universe underwent a brief but stupendously accelerated expansion immediately following the big bang.

“The implications for this detection stagger the mind,” said co-leader Jamie Bock from Caltech. “We are measuring a signal that comes from the dawn of time.”

BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) scans the sky from the south pole, looking for a subtle effect in the cosmic microwave background (CMB) — the radiation released 380,000 years after the Big Bang when the universe cooled enough to allow photons to travel freely across the cosmos.

The CMB fills every cubic centimeter of the observable universe with approximately 400 microwave photons. The so-called afterglow of the big bang is nearly uniform in all directions, but small residual variations (on the level of one in 100,000) in temperature show a specific pattern. These irregularities match what would be expected if minute quantum fluctuations had ballooned to the size of the observable universe today.

So astronomers dreamed up the theory of inflation — the epoch immediately following the big bang (10^-34 seconds later) when the universe expanded exponentially (by at least a factor of 10²⁵) — causing quantum fluctuations to magnify to cosmic size. Not only does inflation help explain why the universe is so smooth on such massive scales, but also why it’s flat when there’s an infinite number of other possible curvatures.

While inflation is a pillar of big bang cosmology, it has remained purely a theoretical framework. Many astronomers don’t buy it as we can’t explain what physical mechanism would have driven such a massive expansion, let alone stop it. The results announced today provide a strong case in support of inflation.

In Depth: We’ve Discovered Inflation! Now What?

The trick is in looking at the CMB where inflation’s signature is imprinted as incredibly faint patterns of polarized light — some of the light waves have a preferred plane of vibration. If a gravitational wave passes through the fabric of spacetime it will squeeze spacetime in one direction (making it hotter) and stretch it in another (making it cooler). Inflation will then amplify these quantum fluctuations into a detectable signal: the hotter and therefore more energetic photons will be visible in the CMB, leaving a slight polarization imprint.

This effect will create two distinct patterns: E-modes and B-modes, which are differentiated based on whether or not they have even or odd parity. In simpler terms: E-mode patterns will look the same when reflected in a mirror, whereas B-mode patterns will not.

E-modes have already been extensively detected and studied. While both are the result of primordial gravitational waves, E-modes can be produced through multiple mechanisms whereas B-modes can only be produced via primordial gravitational waves. Detecting the latter is a clean diagnostic — or as astronomers are putting it: “smoking gun evidence” — of inflation, which amplified gravitational waves in the early Universe.

“The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky,” said co-leader Chao-Lin Kuo from Stanford University, designer of the BICEP2 detector.

The team analyzed sections of the sky spanning one to five degrees (two to 10 times the size of the full moon) for more than three years. They created a unique array of 512 detectors, which collectively operate at a frosty 0.25 Kelvin. This new technology enabled them to make detections at a speed 10 times faster than before.

The results are surprisingly robust, with a 5.9 sigma detection. For comparison, when particle physicists announced the discovery of the Higgs Boson in July, 2012 they had to reach at least a 5 sigma result, or a confidence level of 99.9999 percent. At this level, the chance that the result is erroneous due to random statistical fluctuations is only one in a million. Those are pretty good odds.

While the team was careful to rule out any errors, it will be crucial for another team to verify these results. The Planck spacecraft, which has been producing exquisite measurements of the CMB, will be reporting its own findings later this year. At least a dozen other teams have also been searching for this signature.

“This work offers new insights into some of our most basic questions: Why do we exist? How did the universe begin?” commented Harvard theorist Avi Loeb. “These results are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was.”

Not only does inflation succeed in explaining the origin of cosmic structure — how the cosmic web formed from the smooth aftermath of the big bang — but it makes wilder predictions as well. The model seems to produce not just one universe, but rather an ensemble of universes, otherwise known as a multiverse. This collection of universes has no end and no beginning, continuing to pop up eternally.

Today’s results provide a stronger case for “eternal inflation,” which gives a new perspective on our desolate place within the cosmos. Not only do we live on a small planet orbiting one star out of hundreds of billions, in one galaxy out of hundreds of billions, but our entire universe may just be one bubble out of a vast cosmic ocean of others.

The detailed paper may be found here.
The full set of papers are here.
An FAQ summarizing the data is here.

March 12, 2014March 8, 2017 by Fraser Cain

What Is The Cosmic Microwave Background Radiation?

The Cosmic Microwave Background Radiation is the afterglow of the Big Bang; one of the strongest lines of evidence we have that this event happened. UCLA’s Dr. Ned Wright explains.

“Ok, I’m Ned Wright, and I’m a professor of physics and astronomy at UCLA, and I work on infrared astronomy and cosmology.”

How useful is the cosmic microwave background radiation?

“Well, the most important information we get is from the cosmic microwave background radiation come from, at the lowest level, is it’s existence. When I started in astronomy, it wasn’t 100 percent certain that the Big Bang model was correct. And so with the prediction of a cosmic microwave background from the Big Bang and the prediction of no cosmic microwave background from the competing theory, the steady state, that was a very important step in our knowledge.”

“And then the second aspect of the cosmic microwave background that is very important, is that it’s spectrum is extremely similar to a black body. And so, by being a black body means that universe relatively smoothly transitioned from being opaque to being transparent, and then we actually see effectively an isothermal cavity when we look out, so it looks very close to a black body.”

“And the fact that we are moving through the universe can be measured very precisely by looking at what is called the dipole anisotropy of the microwave background. So one side of the sky is slightly hotter (about 3 millikelvin hotter) and one side of the sky – the opposite side of the sky – is slightly colder (about 3 millikelvin colder), so that means that we are moving at approximately a tenth of a percent of the speed of light. And in fact we now know very precisely what that value is – it’s about 370 kilometers per second. So that’s our motion, the solar system’s motion, through the universe.”

“An then the final piece of information we’re getting from the microwave background now, in fact the Planck satellite just gave us more information along these lines is measurement of the statistical pattern of the very small what I call anisotropies or little bumps and valleys in the temperature. So in addition to the 3 millikelvin difference, we actually have plus or minus 100 microkelvin difference in the temperature from different spots. And so, when you look at these spots, and look at their detailed pattern, you can actually see a very prominent feature, which is there’s about a one and a half degree preferred scale, and that’s what’s caused by the acoustic
waves that are set up by the density perturbations early in the history of the universe, and how far they could travel before the universe became transparent. And that’s a very strong indicator about the universe.”

What does it tell us about dark energy?

“The cosmic microwave background actually has this pattern on a half degree scale, and that gives you effectively a line of position, as you have with celestial navigation where you get a measurement of one star with a sextant, then you get a line on the map where you are. But you can look at the same pattern – the acoustic wave setup in the universe, and you see that in the galaxy’s distribution a lot more locally. We’re talking about galaxies, so it might be a billion light years away, but to cosmologists, that’s local. And these galaxies also show the same wave-like pattern, and you can measure that angle at scale locally and compare it to what you see in history and that gives you the crossing line of position. And that really tells us where we are in the universe, and how much stuff there is and it tells us that we have this dark energy which nobody really understands what it is, but we know what it’s doing. It’s making the universe accelerate in it’s expansion.”

March 6, 2014March 8, 2017 by Fraser Cain

Why Is This A Special Time For The Universe?

You might be surprised to know that you’re living in a very special time in the Universe. And in the far future, our descendant astronomers will wish they could live in such an exciting time Let’s find out why.

You might be interested to know that you are living in a unique important and special time in the age of the Universe. Our view of the night sky won’t be around forever, in fact, as we think about the vast time that lies ahead, our time in the Universe will sound very special.

Astronomers figure the Universe has been around for 13.8 billion years. Everything in the entire Universe was once collected together into a singularity of space and time. And then, in a flash, Big Bang. Within a fraction of a second, the fundamental forces of the Universe came into existence, followed by the earliest types of matter and energy. For a few minutes, the entire Universe was like a core of a star, fusing hydrogen into helium. Approximately 377,000 years after the Big Bang, the entire Universe had cooled to the point that it became transparent. We see this flash of released light as the Cosmic Microwave Background Radiation.

Over the next few billion years, the first stars and galaxies formed, leading to the large scale structures of the Universe. These new galaxies with their furious star formation would have been an amazing sight. It would have been a very special time in the Universe, but it’s not our time.

Over the next few billion years, the Universe continued to expand. And it was during this time that the mysterious force called dark energy crept in, further driving the expansion of the Universe. We don’t know what dark energy is, but we know it’s a constant pressure that’s accelerating the expansion of the Universe.

As the volume of the Universe increases, the rate of its expansion increases. And over vast periods of time, it’ll make the Universe unrecognizable from what we see today. The further we look out into space, the faster galaxies are moving away from us. There are galaxies moving away from us faster than the speed of light. In other words, the light from those galaxies will never reach us.

The Universe 1.9 billion years after the Big Bang. Credit: Alvaro Orsi, Institute for Computational Cosmology, Durham University.

As dark energy increases, more and more galaxies will cross this cosmic horizon, invisible to us forever. And so, we can imagine a time in the far future, where the Cosmic Microwave Background Radiation has been stretched away until it’s undetectable. And eventually there will be a time when there will be no other galaxies visible in the night sky. Future astronomers will see a Universe without a cosmological history. There will be no way to know that there was ever a Big Bang, that there was ever a large scale structure to the Universe.

So how long will this be? According to Dr. Lawrence Krauss and Robert J. Scherrer, in as soon as 100 billion years, there will be no way to see other galaxies and calculate their velocity away from us. That sounds like a long time, but there are red dwarf stars that could live for more than a trillion years. We will have lost our history forever.

Cherish and make the most of these next hundred billion years. Keep our history alive and remember to tell our great great grandchildren and their robotic companions the tales of a time when we knew about the Big Bang.

What about you? What would you go see if you could witness any astronomical event in the history of the universe?

February 15, 2014December 23, 2015 by Jason Major

NOvA Experiment Nabs Its First Neutrinos

The NUmI (Neutrinos from the Main Injector) horn at Fermilab, which fires protons that degrade into neutrinos. (Image: Caltech)

Neutrinos are some of the most abundant, curious, and elusive critters in particle physics. Incredibly lightweight — nigh massless, according to the Standard Model — as well as chargeless, they zip around the Universe at the speed of light and they don’t interact with any other particles. Some of them have been around since the Big Bang and, just as you’ve read this, trillions of them have passed through your body (and more are on the way.) But despite their ubiquitousness neutrinos are notoriously difficult to study precisely because they ignore pretty much everything made out of anything else. So it’s not surprising that weighing a neutrino isn’t as simple as politely asking one to step on a scale.

Thankfully particle physicists are a tenacious lot, including the ones at the U.S. Department of Energy’s Fermilab, and they aren’t giving up on their latest neutrino safari: the NuMI Off-Axis Electron Neutrino Appearance experiment, or NOvA. (Scientists represent neutrinos with the Greek letter nu, or v.) It’s a very small-game hunt to catch neutrinos on the fly, and it uses some very big equipment to do the job. And it’s already captured its first neutrinos — even before their setup is fully complete.

Created by smashing protons against graphite targets in Fermilab’s facility just outside Chicago, Illinois, resulting neutrinos are collected and shot out in a beam 500 miles northwest to the NOvA far detector in Ash River, Minnesota, located along the Canadian border. The very first beams were fired in Sept. 2013, while the Ash River facility was still under construction.

One of the first detections by NOvA of Fermilab-made neutrinos (Image courtesy of NOvA collaboration)

“That the first neutrinos have been detected even before the NOvA far detector installation is complete is a real tribute to everyone involved,” said University of Minnesota physicist Marvin Marshak, Ash River Laboratory director. “This early result suggests that the NOvA collaboration will make important contributions to our knowledge of these particles in the not so distant future.”

The 500-mile (800 km) path of the NOvA neutrino beam (Fermilab) — The 500-mile (800 km) subterranean path of the NOvA neutrino beam (Fermilab)

The beams from Fermilab are fired in two-second intervals, each sending billions of neutrinos directly toward the detectors. The near detector at Fermilab confirms the initial “flavor” of neutrinos in the beam, and the much larger far detector then determines if the neutrinos have changed during their three-millisecond underground interstate journey.

Again, because neutrinos don’t readily interact with ordinary particles, the beams can easily travel straight through the ground between the facilities — despite the curvature of the Earth. In fact the beam, which starts out 150 feet (45 meters) below ground near Chicago, eventually passes over 6 miles (10 km) deep during its trip.

According to a press release from Fermilab, neutrinos “come in three types, called flavors (electron, muon, or tau), and change between them as they travel. The two detectors of the NOvA experiment are placed so far apart to give the neutrinos the time to oscillate from one flavor to another while traveling at nearly the speed of light. Even though only a fraction of the experiment’s larger detector, called the far detector, is fully built, filled with scintillator and wired with electronics at this point, the experiment has already used it to record signals from its first neutrinos.”

The 50-foot (15 m) tall detector blocks are filled with a liquid scintillator that’s made of 95% mineral oil and 5% liquid hydrocarbon called pseudocumene, which is toxic but “imperative to the neutrino-detecting process.” The mixture magnifies any light that hits it, allowing the neutrino strikes to be more easily detected and measured. (Source)

“NOvA represents a new generation of neutrino experiments,” said Fermilab Director Nigel Lockyer. “We are proud to reach this important milestone on our way to learning more about these fundamental particles.”

One of NOvA's 28 detectors (Fermilab) — One of NOvA’s 28 far detector blocks (Fermilab)

After completion this summer NOvA’s near and far detectors will weigh 300 and 14,000 tons, respectively.

The goal of the NOvA experiment is to successfully capture and measure the masses of the different neutrino flavors and also determine if neutrinos are their own antiparticles (they could be the same, since they lack specific charge.) By comparing the oscillations (i.e., flavor changes) of muon neutrino beams vs. muon antineutrino beams fired from Fermilab, scientists hope to determine their mass hierarchy — and ultimately discover why the Universe currently contains much more matter than antimatter.

Once the experiment is fully operational scientists expect to catch a precious few neutrinos every day — about 5,000 total over the course of its six-year run. Until then, they at least now have their first few on the books.

“Seeing neutrinos in the first modules of the detector in Minnesota is a major milestone. Now we can start doing physics.”
– Rick Tesarek, Fermilab physicist

Learn more about the development and construction of the NoVA experiment below:

(Video credit: Fermilab)

Find out more about the NOvA research goals here.

Source: Fermilab press release

The NOvA collaboration is made up of 208 scientists from 38 institutions in the United States, Brazil, the Czech Republic, Greece, India, Russia and the United Kingdom. The experiment receives funding from the U.S. Department of Energy, the National Science Foundation and other funding agencies.

February 10, 2014March 8, 2017 by Fraser Cain

How Old is the Universe?

The Universe is vast bubble of space and time, expanding in volume. Run the clock backward and you get to a point where everything was compacted into a microscopic singularity of incomprehensible density. In a fraction of a second, it began expanding in volume, and it’s still continuing to do so today.

So how old is the Universe? How long has it been expanding for? How do we know? For a good long while, Astronomers assumed the Earth, and therefore the Universe was timeless. That it had always been here, and always would be.

In the 18th century, geologists started to gather evidence that maybe the Earth hadn’t been around forever. Perhaps it was only millions or billions of years old. Maybe the Sun too, or even… the Universe. Maybe there was a time when there was nothing? Then, suddenly, pop… Universe.

It’s the science of thermodynamics that gave us our first insight. Over vast lengths of time, everything moves towards entropy, or maximum disorder. Just like a hot coffee cools down, all temperatures want to average out. And if the Universe was infinite in age, everything should be the same temperature. There should be no stars, planets, or us.

The brilliant Belgian priest and astronomer, George Lemaitre, proposed that the Universe must be either expanding or contracting. At some point, he theorized, the Universe would have been an infinitesimal point – he called it the primeval atom. And it was Edwin Hubble, in 1929 who observed that distant galaxies are moving away from us in all directions, confirming Lemaitre’s theories. Our Universe is clearly expanding.

Which means that if you run the clock backwards, and it was smaller in the distant past. And if you go back far enough, there’s a moment in time when the Universe began. Which means it has an age. The next challenge… figuring out the Universe’s birthdate.

Time line of the Universe (Credit: NASA/WMAP Science Team)

In 1958, the astronomer Allan Sandage used the expansion rate of the Universe, otherwise known as the Hubble Constant, to calculate how long it had probably been expanding. He came up with a figure of approximately 20 billion years. A more accurate estimation for the age of the Universe came with the discovery of the Cosmic Microwave Background Radiation; the afterglow of the Big Bang that we see in every direction we look.

Approximately 380,000 years after the Big Bang, our Universe had cooled to the point that protons and electrons could come together to form hydrogen atoms. At this point, it was a balmy 3000 Kelvin. Using this and by observing the background radiation, and how far the wavelengths of light have been stretched out by the expansion, astronomers were able to calculate how long it has been expanding for.

Initial estimates put the age of the Universe between 13 and 14 billion years old. But recent missions, like NASA’s WMAP mission and the European Planck Observatory have fine tuned that estimate with incredible accuracy. We now know the Universe is 13.8242 billion years, plus or minus a few million years.

We don’t know where it came from, or what caused it to come into being, but we know exactly how our Universe is. That’s a good start.

December 18, 2013March 14, 2017 by Fraser Cain

What Is The Big Rip?

Dr. Thad Szabo is a professor of physics and astronomy at Cerritos College. He’s also a regular contributor to many of our projects, like the Virtual Star Party and the Weekly Space Hangout. Thad has an encyclopedic knowledge of all things space, so we got him to explain a few fascinating concepts.

In this video, Thad explains the strange mystery of dark energy, and the even stranger idea of the Big Rip.

What is the ‘Big Rip?’

If we look at the expansion of the universe, at first it was thought that, as things are expanding while objects have mass, the mass is going to be attracted to other mass, and that should slow the expansion. Then, in the late 1990’s, you have the supernova surveys that are looking deeper into space than we’ve ever looked before, and measuring distances accurately to greater distances than we’ve ever seen before. Something really surprising came out, and that was what we’ll now use “dark energy” now to explain, and that is that the acceleration is not actually slowing down – it’s not even stopped. It’s actually getting faster, and if you look at the most distant objects, they’re actually moving away from us and the acceleration is increasing the acceleration of expansion. This is actually a huge result.

One of the ideas of trying to explain it is to use the “cosmological constant,” which is something that Einstein actually introduced to his field equations to try to keep the universe the same size. He didn’t like the idea of a universe changing, so he just kind of cooked up this term and threw it into the equations to say, alright, well if it isn’t supposed to expand or contract, if I make this little mathematical adjustment, it stays the same size.

Hubble comes along about ten years later, and is observing galaxies and measuring their red shifts and their distances, and says wait a minute – no the universe is expanding. And actually we should really credit that to Georges Lemaître, who was able to interpret Hubble’s data to come up with the idea of what we now call the Big Bang.

So, the expansion’s happening – wait, it’s getting faster. And now the attempt is to try to understand how dark energy works. Right now, most of the evidence points to this idea that the expansion will continue in the space between galaxies. That the forces of gravity, and especially magnetism and the strong nuclear force that holds protons and neutrons together in the center of an atom, would be strong enough that dark energy is never going to be able to pull those objects apart.

However, there’s a possibility that it doesn’t work like that. There’s actually a little bit of experimental evidence right now that, although it’s not well-established, that there’s a little bit of a bias with certain experiments that dark energy may get stronger over time. And, if it does so, the distances won’t matter – that any object will be pulled apart. So first, you will see all galaxies recede from each other, as space starts to grow bigger and bigger, faster and faster. Then the galaxies will start to be pulled apart. Then star systems, then planets from their stars, then stars themselves, and then other objects that would typically be held together by the much stronger forces, the electromagnetic force objects held by that will be pulled apart, and then eventually, nuclei in atoms.

So if dark energy behaves so that it gets stronger and stronger over time, it will eventually overcome everything, and you’ll have a universe with nothing left. That’s the ‘Big Rip’ – if dark energy gets stronger and stronger over time, it will eventually overcome any forces of attraction, and then everything is torn apart.

You can find more information from Dr. Thad Szabo at his YouTube channel.

December 16, 2013March 14, 2017 by Fraser Cain

Can Stars Collide?

Imagine a really bad day. Perhaps you’re imagining a day where the Sun crashes into another star, destroying most of the Solar System.

No? Well then, even in your imagination things aren’t so bad… It’s all just matter of perspective.

Fortunately for us, we live in out the boring suburbs of the Milky Way. Out here, distances between stars are so vast that collisions are incredibly rare. There are places in the Milky Way where stars are crowded more densely, like globular clusters, and we get to see the aftermath of these collisions. These clusters are ancient spherical structures that can contain hundreds of thousands of stars, all of which formed together, shortly after the Big Bang.

Within one of these clusters, stars average about a light year apart, and at their core, they can get as close to one another as the radius of our Solar System. With all these stars buzzing around for billions of years, you can imagine they’ve gotten up to some serious mischief.

Within globular clusters there are these mysterious blue straggler stars. They’re large hot stars, and if they had formed with the rest of the cluster, they would have detonated as supernovae billions of years ago. So scientists figure that they must have formed recently.

How? Astronomers think they’re the result of a stellar collision. Perhaps a binary pair of stars merged, or maybe two stars smashed into one another.

Professor Mark Morris of the University of California at Los Angeles in the Department of Physics and Astronomy helps to explain this idea.

“When you see two stars colliding with each other, it depends on how fast they’re moving. If they’re moving at speeds like we see at the center of our galaxy, then the collision is extremely violent. If it’s a head-on collision, the stars get completely splashed to the far corners of the galaxy. If they’re merging at slower velocities than we see at our neck of the woods in our galaxy, then stars are more happy to merge with us and coalesce into one single, more massive object.”

There’s another place in the Milky Way where you’ve got a dense collection of stars, racing around at breakneck speeds… near the supermassive black hole at the center of the galaxy.

This monster black hole contains the mass of 4 million times the Sun, and dominates the region around the center of the Milky Way.

This artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Supermassive black holes are enormously dense objects buried at the hearts of galaxies. Image credit: NASA/JPL-Caltech — Supermassive black holes are enormously dense objects buried at the hearts of galaxies. Image credit: NASA/JPL-Caltech

“The core of the Milky Way is one of those places where you find the extremes of nature. The density of stars there is higher than anywhere else in the galaxy,”Professor Morris continues. “Overall, in the center of our galaxy on scales of hundreds of light years, there is much more gas present than anywhere else in the galaxy. The magnetic field is stronger there than anywhere else in the galaxy, and it has it’s own geometry there. So it’s an unusual place, an energetic place, a violent place, because everything else is moving so much faster there than you see elsewhere.”

“We study the stars in the immediate vicinity of the black hole, and we find that there’s not as many stars as one might have expected, and one of the explanations for that is that stars collide with each other and either eliminate one another or merge, and two stars become one, and both of those processes are probably occurring.”

Stars whip around it, like comets dart around our Sun, and interactions are commonplace.

There’s another scenario that can crash stars together.

The Milky Way mostly has multiple star systems. Several stars can be orbiting a common center of gravity. Many are great distances, but some can have orbits tighter than the planets around our Sun.

When one star reaches the end of its life, expanding into a red giant, It can consume its binary partner. The consumed star then strips away 90% of the mass of the red giant, leaving behind a rapidly pulsating remnant.

What about when galaxies collide? That sounds like a recipe for mayhem.
Surprisingly, not so much.

“That’s actually a very interesting question, because if you imagine two galaxies colliding, you’d imagine that to be an exceptionally violent event,’ Professor Morris explains. “But in fact, the stars in those two galaxies are relatively unaffected. The number of stars that will collide when two galaxies collide is possibly counted on the fingers of one or two hands. Stars are so few and far between that they just aren’t going to meet each other with any significance in a field like that.”

Galaxy mergers, such as the Mice Galaxies will be part of Galaxy Zoo's newest project. Credit: Hubble Space Telescope — The Mice galaxies merging. Credit: Hubble Space Telescope

“What you see when you see two galaxies collide, however, on the large scale, is that the tidal forces of the two galaxies will rip each of the galaxies apart in terms of what it will look like. Streams of stars will be strewn out in various directions depending on the precise history of the interaction between the two galaxies. And so, eventually over time, the galaxies will merge, the whole configuration of stars will settle down into something that looks unlike either of the two initially colliding galaxies. Perhaps something more spheroidal or spherical, and it might look more like an elliptical galaxy than the spiral galaxy that these two galaxies now are.”

Currently, we’re on a collision course with the Andromeda Galaxy, and it’s expected we’ll smash into it in about 4 billion years. The gas and dust will collide and pile up, igniting an era of furious star formation. But the stars themselves? They’ll barely notice. The stars in the two galaxies will just streak past each other, like a swarm of angry bees.

Phew.

So, good news! When you’re imagining a worse day, you won’t have to worry about our Sun colliding with another star. We’re going to be safe and sound for billions of years. But if you live in a globular cluster or near the center of the galaxy, you might want to check out some property here in the burbs.

Thanks to Professor Mark Morris at UCLA – visit their Physics and Astronomy program homepage here.

December 12, 2013March 14, 2017 by Fraser Cain

Is Everything in the Universe Expanding?

The Universe is expanding. Distant galaxies are moving away from us in all directions. It’s natural to wonder, is everything expanding? Is the Milky Way expanding? What about the Solar System, or even objects here on Earth. Are atoms expanding?

Nope. The only thing expanding is space itself. Imagine the Universe as loaf of raisin bread rising in the oven. As the bread bakes, it’s stretching in all directions – that’s space. But the raisins aren’t growing, they’re just getting carried away from each other as there’s more bread expanding between them.

Space is expanding from the Big Bang and the acceleration of dark energy. But the objects embedded in space, like planets, stars, and galaxies stay exactly the same size. As space expands, it carries galaxies away from each other. From our perspective, we see galaxies moving away in every direction. The further galaxies are, the faster they’re moving.

There are a few exceptions. The Andromeda Galaxy is actually moving towards the Milky Way, and will collide with us in about 4 billion years.In this case, the pull of gravity between the Milky Way and Andromeda is so strong that it overcomes the expansion of the Universe on a local level.

Within the Milky Way, gravity holds the stars together, and same with the Solar System. The nuclear force holding atoms together is stronger than this expansion at a local scale. Is this the way it will always be? Maybe. Maybe not.

A few decades ago, astronomers thought that the Universe was expanding because of momentum left over from the Big Bang. But with the discovery of dark energy in 1998, astronomers realized there was a new possibility for the future of the Universe. Perhaps this accelerating dark energy might be increasing over time.

In billions years from now, the expansive force might overcome the gravity that holds galaxies together. Eventually it would become so strong that star systems, planets and eventually matter itself could get torn apart.This is a future for the Universe known as the Big Rip. And if it’s true, then the space between stars, planets and even atoms will expand in the far future.

This image shows the Hubble Ultra Deep Field 2012, an improved version of the Hubble Ultra Deep Field image featuring additional observation time. The new data have revealed for the first time a population of distant galaxies at redshifts between 9 and 12, including the most distant object observed to date. These galaxies will require confirmation using spectroscopy by the forthcoming NASA/ESA/CSA James Webb Space Telescope before they are considered to be fully confirmed. — The space between the galaxies is expanding. Credit: NASA/HST

Is this going to happen? Astronomers don’t know. Their best observations so far can’t rule it out, or confirm it. And so, future observations and space missions will try to calculate the rate of dark energy’s expansion.

So no, matter on a local level isn’t expanding. The spaces between planets and stars isn’t growing. Only the distances between galaxies which aren’t gravitationally bound to each other is increasing. Because space itself is expanding.