Category: cosmology

Space Wasn’t Always A Big Place

“It’s true that we don’t know how large the unobservable part of the Universe truly is; it may be infinite. It’s also true that we don’t know how long inflation endured for or what, if anything, came before it. But we do know that when the hot Big Bang began, all the matter and energy that we see in our visible Universe today  all the stuff that extends for 46.1 billion light-years in all directions  must have been concentrated into a volume of around the size of a soccer ball.

For at least a short period of time, the vast expanse of space that we look out and observe today was anything but big. All the matter making up entire massive galaxies would have fit into a region of space smaller than a pencil eraser. And yet, through 13.8 billion years of expansion, cooling, and gravitation, we arrive at the vast Universe we occupy a tiny corner of today. Space may be the biggest thing we know of, but the size of our observable Universe is a recent achievement. Space wasn’t always so big, and the evidence is written on the Universe for all of us to see.”

If you take stock of our Universe as we see it today, you’ll find that it’s 46.1 billion light-years to the limits of what’s observable. Contained in that vast volume are some 2 trillion galaxies, typically containing hundreds of billions of stars apiece. And yet, if you think about our picture of the Big Bang, its tells us that all of this must have been smaller, hotter, and denser in the distant past.

It’s enough to make you wonder: by how much? How big a place was space in the early days? Luckily, physics, astronomy, and cosmology have the answers, and now so can you.

5 Things We Know About Dark Matter (And 5 We Don’t)

“It’s possible we’ll get an announcement of a candidate dark matter particle at any point from a variety of experiments, but it’s also possible that the ways in which we’re presently looking for dark matter will never bear fruit. Nevertheless, we not only know that dark matter exists from the astrophysical evidence, but we’ve definitively uncovered a large amount of information about what it is, how it behaves, and what it cannot be. In the quest to understand our Universe, one thing stands out above all others: we must be intellectually scrupulous and honest about what we know, what we don’t, and what remains uncertain.”

There’s always a lot of buzz about dark matter, but most of it is misinformation either from zealots eager to dismiss it or theorists clamoring for people to latch onto their latest wild (and unsupported) idea. But the real scientific truth is that we are absolutely certain that dark matter (or something very, very much like it) is present, and has properties that we can test for and measure in astrophysical environments. But it’s simultaneously true that there are a number of open questions about dark matter that we don’t have the first clue what the answer will turn out to be, and must remain open to the possibilities.

Here’s a great list of five things we actually know about dark matter (plus how we know it), along with five things that still remain obscure to us all.

Ask Ethan: Does Dark Energy Gravitate?

“Does dark energy gravititate? In other words does the increase in dark energy as space expands also create more gravity?”

Dark energy is the name we give to whatever’s responsible for the accelerated expansion of the Universe. According to our best theory of gravity, General Relativity, dark energy does indeed have an energy density, which doesn’t appear to be changing over time. This is bizarre, because for everything else, like matter and radiation, the fact that the Universe is expanding means that the density of “stuff” dilutes as time goes on. But for dark energy, it’s a form of energy that appears to be inherent to space itself, meaning that as the Universe expands, its density never goes down. You might think that adding more and more energy in the Universe would just cause it to gravitate more and more severely, though, eventually leading to a recollapse. That’s not what’s going on at all, though.

Why doesn’t dark energy lead to a recollapse? Does this mean the expanding Universe violates the conservation of energy? And what does it mean for dark energy to gravitate? Come get the answers today.

These 4 Pieces Of Evidence Have Already Taken Us Beyond The Big Bang

“There are other predictions of cosmic inflation, too. Inflation predicts that the Universe should be almost perfectly flat, but not quite, with the degree of curvature falling somewhere within 0.0001% and 0.01%. The scalar spectral index, measured to depart slightly from scale invariance, should “roll” (or change during the final stages of inflation) by about 0.1%. And there should be a set of not just density fluctuations, but gravitational wave fluctuations that arise from inflation. So far, observations are consistent with all of these, but we have not reached the level of precision necessary to test them.

But four independent tests are more than enough to draw a conclusion. Despite the voices of a few detractors who refuse to accept this evidence, we can now confidently state that we’ve gone before the Big Bang, and cosmic inflation led to the birth of our Universe. The next question, of what happened prior to the end of inflation, is now at the frontier of 21st century cosmology.”

Did the Universe really begin with a Big Bang? Although there’s an overwhelming suite of evidence in support of our modern Universe arising from a very hot, dense, expanding state a finite amount of time ago, the Big Bang is not the origin of our Universe. For decades, now, we’ve had multiple lines of evidence that demonstrate that no, you cannot extrapolate the Big Bang all the way back to arbitrarily high energies and densities: to a singularity. But a series of puzzles led to a spectacular idea: cosmic inflation, which could have set up and preceded the Big Bang. While inflation’s detractors frequently make the news, the scientific data is overwhelmingly in favor of it. 

Inflation has made concrete predictions, and of the ones that have been tested, inflation is 4-for-4. Come learn what lies beyond the Big Bang today.

The Expanding Universe Might Not Depend On How You Measure It, But When

“It’s definitely the case that different methods of measuring the expanding Universe give different values, but this is the first time that the same method has yielded two different results depending on whether you look at the full data set or the late-time measurements alone. The expansion rate of the Universe has been one of the most contentious issues in all of modern science — the Hubble space telescope was even named for its main science goal of measuring that rate, also known as the Hubble constant — and this new result provides a major clue.

Could factoring the effect of cosmic voids in all measurements account for the full discrepancy? Could we be seeing evidence that something, even if it’s not dark energy, is evolving in the Universe in an unexpected fashion? Or, quite possibly, could this be a suggestion that it’s the cosmic microwave background data that’s somehow mistaken, after all? One thing is clear: more and better data, which should be on the way with Euclid, LSST, and WFIRST, will help us decide.”

If you measure the current-day expansion rate of the Universe by looking back and measuring the distances and redshifts to various objects, you get a particular value of around 74 km/s/Mpc. On the other hand, if you look at the earliest light from the Universe, like from the cosmic microwave background, you get a different, inconsistent value of 67 km/s/Mpc. Now, using data from the large-scale structure of the Universe, a new team has discovered something remarkable: if they use all of their data, and factor in the effects of cosmic voids, they get an in-between value of 69 km/s/Mpc. On the other hand, if they restrict themselves to relatively nearby measurements, they get a much higher value: closer to 72.3 km/s/Mpc.

What, exactly, is going on? This is a presently unsolved puzzle in cosmology, but this new study reveals one more clue that brings us closer to understanding what’s happening.

Don’t Believe These 5 Myths About The Big Bang

1.) The Big Bang is the explosion that began our Universe. Every time we look out at a distant galaxy in the Universe and try to measure what its light is doing, we see the same pattern emerge: the farther away the galaxy is, the more significantly its light is systematically shifted to longer and longer wavelengths. This redshift that we observe for these objects follows a predictable pattern, with double the distance meaning that the light is shifted by twice as much.

Distant objects, therefore, appear to be receding away from us. Just as a police car speeding away from you will sound lower-pitched the faster it moves away from you, the greater we measure an object’s distance to be from us, the greater the measured redshift of its light will be. It makes a lot of sense, then, to think that the more distant objects are moving away from us at faster speeds, and that we could trace every galaxy we see today back to a single point in the past: an enormous explosion.”

The Big Bang is not an explosion, it doesn’t have a center point that we can trace the expansion back to, it never reached an infinitely hot-and-dense state, it doesn’t imply that the Universe began from a singularity, and it doesn’t take you back to a moment where space, time, and the laws of physics all spontaneously emerged. Do you believe any of these statements? Do you know why they’re not true? 

Here’s the real physics behind what we know about our Universe’s origin, with the scientific evidence to back it all up!

Our Home Supercluster, Laniakea, Is Dissolving Before Our Eyes

“Every supercluster that we’ve ever identified are not only gravitationally unbound from one another, but they themselves are not gravitationally bound structures. The individual groups and clusters within a supercluster are unbound, meaning that as time goes on, each structure presently identified as a supercluster will eventually dissociate. For our own corner of the Universe, the Local Group will never merge with the Virgo cluster, the Leo I group, or any structure larger than our own.

On the largest cosmic scales, enormous collections of galaxies spanning vast volumes of space appear to be real ⁠— the Universe’s superclusters ⁠— but these apparent structures are ephemeral and transient. They are not bound together, and they will never become so. In fact, if a structure had not already accumulated enough mass 6 billion years ago to become bound, when dark energy first dominated the Universe’s expansion, it never will. Billions of years from now, the individual supercluster components will be torn apart by the Universe’s expansion, forever adrift as lonesome islands in the great cosmic ocean.”

If someone asks you for your cosmic address, you’d tell them where you were here on Earth, followed by the Earth’s position orbiting our Sun, the Sun in motion around the Milky Way galaxy, the Milky Way’s membership in the Local Group, which itself lies on the outskirts of the Virgo cluster, which lives in our home supercluster: Laniakea.

Except there are a few problems with this. The Virgo cluster and the Local Group are not bound together; they are receding away with the expansion of the Universe, and while each one will remain bound individually, they will never encounter one another. It’s even worse for Laniakea, our local supercluster, which includes many galactic groups and clusters. 

Unfortunately, Laniakea is only an apparent structure; in reality, it’s completely unbound, and is dissolving before our very eyes.

Ask Ethan: How Can We See 46.1 Billion Light-Years Away In A 13.8 Billion Year Old Universe?

“If the limit of what we could see in a 13.8 billion year old Universe were truly 13.8 billion light-years, it would be extraordinary evidence that both General Relativity was wrong and that objects could not move from one location to a more distant location in the Universe over time. The observational evidence overwhelming indicates that objects do move, that General Relativity is correct, and that the Universe is expanding and dominated by a mix of dark matter and dark energy.

When you take the full suite of what’s known into account, we discover a Universe that began with a hot Big Bang some 13.8 billion years ago, has been expanding ever since, and whose most distant light can come to us from an object presently located 46.1 billion light-years away. The space between ourselves and the distant, unbound objects we observe continues to expand at a rate of 6.5 light-years per year at the most distant cosmic frontier. As time goes on, the distant reaches of the Universe will further recede from our grasp.”

The fabric of space is expanding, and this is perhaps the most counterintuitive thing of all. Back in the earliest stages of the Big Bang, a point in space no farther away from us than the length of a city block could have emitted a photon, and it would take that photon a remarkable 13.8 billion years just to reach us. Moreover, that photon would journey for a total of 13.8 billion light-years before arriving at our eyes, and an object located at the exact same point in space where it was initially emitted from would now be 46.1 billion light-years away from us.

Why is this? Because that’s what the laws of General Relativity, coupled with our knowledge of what’s present in the Universe, demand of space and time. Come get the full story today!

How Far Is It To The Edge Of The Universe?

“If you define the edge of the Universe as the farthest object we could ever reach if we began our journey immediately, then our present limit is a mere distance of 18 billion light-years, encompassing just 6% of the volume of our observable Universe. If you define it as the limit of what we can observe a signal from — who we can see and who can see us — then the edge goes out to 46.1 billion light-years. But if you define it as the limits of the unobservable Universe, the only limit we have is that it’s at least 1,150 billion light-years in size, and it could be even larger.

This doesn’t necessarily mean that the Universe is infinite, though. It could be flat and still curve back on itself, with a donut-like shape known mathematically as a torus. As large and expansive as the observable Universe is, it’s still finite, with a finite amount of information to teach us. Beyond that, the ultimate cosmic truths still remain unknown to us.”

How far is it to the edge of the Universe? If you were to leave in a rocket ship today at the speed of light, what is the most distant object you’d be able to visit, and is that truly an edge? If you looked out at the most distant thing you could possibly observe, and the most distant location that could possibly observe us, how far would that be, and is that truly an edge? Or, would you consider the Universe beyond its observable limits, and wonder on the largest scales whose data exists only in our mind’s eye, whether there’s an edge at all?

Regardless of how you think about it, physics has answers, constraints, and limits for how far it truly is to the Universe’s edge. Find out how far it is today!

This Is How Galaxy Cluster Collisions Prove The Existence Of Dark Matter

“When two galaxy clusters collide — a cosmically rare but important event — its internal components behave differently. The intergalactic gas must collide, slow, and heat up, creating shocks and emitting X-rays. If there were no dark matter, this gas, comprising the majority of normal matter, should be the primary source of gravitational lensing. Instead, gravitational lensing maps indicate that most of the mass is displaced from the normal matter.”

Are you disappointed at how readily astronomers seem to accept the idea of dark matter? Does the notion that around 85% of the mass in our Universe isn’t in the form of matter we’re familiar with — stuff like protons, neutrons, and electrons — but instead is some new, undiscovered form of mass that doesn’t collide or interact with light or normal matter in any way? Astronomers only accept it because of the overwhelming observational evidence, and what it does (and doesn’t) indicate. In particular, colliding galaxy clusters tested dark matter against modified gravity directly, and there was a clear winner from the very first one we saw, confirmed over and over again with each new observation.

Come learn about the first empirical proof of dark matter, and why it should absolutely be considered the nail-in-the-coffin of modified gravity theories without dark matter.