dark energy
esiegel | October 25, 2017"Dark matter is interesting. Basically, the Universe is heavier than it should be. There's whole swathes of stuff we can't account for." -Talulah Riley
One of the most puzzling facts about the Universe is that 95% of the energy in it, in the forms of dark matter and dark energy, are completely invisible, and have never been directly detected. Perhaps, the story goes, it’s our theory of gravity that’s to blame, rather than needing new components in the Universe. While dark matter and dark energy can explain a whole slew of observations, gravity modifications do a better job of explaining…
esiegel | September 22, 2017“The more clearly we can focus our attention on the wonders and realities of the universe about us, the less taste we shall have for destruction.” -Rachel Carson
The idea that the spatial fabric of the Universe itself is expanding, and that’s what’s behind the observed relationship between redshift and distance has long been controversial, and also long-misunderstood. After all, if more distant objects appear to recede more quickly, couldn’t there be a different explanation, like an explosion that flung many things outward? As it turns out, this isn’t a mere difference in interpretation,…
esiegel | September 3, 2017“There will be days when we lose faith. Days when our allies turn against us...but the day will never come that we forsake this planet and its people.” ―Optimus Prime
There was too much to simply keep it to a single article a day this week here at Starts With A Bang! The dynamic duo of Megan Watzke and Kimberly Arcand published a delightful contribution on scale, and we're gearing up for a month where we'll highlight some of the telescopes of the 2020s (and maybe beyond) that will help shape the future of astronomy.
In the meantime, those of you who caught totality from the eclipse have…
esiegel | September 1, 2017"For although it is certainly true that quantitative measurements are of great importance, it is a grave error to suppose that the whole of experimental physics can be brought under this heading." -Hendrik Casimir
Ever since we first discovered that the expansion of the Universe is accelerating, scientists have puzzles as to what’s causing it. Although we’ve measured it precisely and concluded that it’s uniform, static in time, and equivalent in its form to a cosmological constant, we still don’t know why it exists. Moreover, any attempts to calculate what its magnitude should be give…
esiegel | May 30, 2017"If you're puzzled by what dark energy is, you're in good company." -Saul Perlmutter
We normally assume that the fundamental constants of the Universe are actually constant, but they don’t have to be that way. They could vary in space, in time, or with the energy density of the Universe, in principle. Before believing in such an extraordinary claim, however, you’d need some remarkable evidence. It’s arguable that exactly that sort of evidence is emerging: from the tensions in the expansion rate of the Universe.
Three different types of measurements, distant stars and galaxies, the large…
esiegel | May 13, 2017"It's everywhere, really. It's between the galaxies. It is in this room. We believe that everywhere that you have space, empty space, that you cannot avoid having some of this dark energy." -Adam Riess
Have you heard about the accelerating Universe? What about dark energy, vacuum energy, or a cosmological constant? These are terms we throw around to talk about one of the strangest observations ever made in the Universe: that the more distant a galaxy is from us, the faster it appears to be receding from us. Not only that, but the rate of recession appears to actually increase over time, which…
esiegel | April 11, 2017"Losing an illusion makes you wiser than finding a truth." -Ludwig Borne
Every so often, an idea comes up in physics claiming that perhaps dark energy isn't real. The ideas focus on one of two lines of thought: either they discount the observational evidence, or they attempt to show that all the calculations are fundamentally flawed.
Measuring back in time and distance (to the left of "today") can inform how the Universe will evolve and accelerate/decelerate far into the future. We can learn that acceleration turned on about 7.8 billion years ago. Image credit: Saul Perlmutter / UC Berkeley…
esiegel | February 25, 2017"The history of astronomy is a history of receding horizons." -Edwin Hubble
As you look to greater and greater distances, you’re looking back in time in the Universe. But thanks to dark energy, what we can see and access today isn’t always going to be accessible. As galaxies grow more distant with the accelerated expansion of the Universe, they eventually recede faster than the speed of light. At present, 97% of the galaxies in the Universe aren’t reachable by us, even at the speed of light.
The observable (yellow) and reachable (magenta) portions of the Universe, which are what they are…
esiegel | February 24, 2017"It's the gravity that shapes the large scale structure of the universe, even though it is the weakest of four categories of forces." -Stephen Hawking
Galaxies don’t just exist in isolation in our Universe, but are often found bound together as a part of even grander structures. Our own Milky Way is bound in a galactic group (our local group), nearby are larger groups and galaxy clusters, and on still larger scales, cosmic superclusters appear to encompass as many as 100,000 individual galaxies.
Outlined in light blue, giant collections of galaxies can be divided up into superclusters. But…
esiegel | January 12, 2017"In the far, far future, essentially all matter will have returned to energy. But because of the enormous expansion of space, this energy will be spread so thinly that it will hardly ever convert back to even the lightest particles of matter. Instead, a faint mist of light will fall for eternity through an ever colder and quieter cosmos." -Brian Greene
It seems like the simplest, most fundamental quantitative question about the expanding Universe of all: how fast is it expanding? Even though it's been more than 80 years since Hubble's most career-defining discovery, we still don't know the…
esiegel | December 30, 2016“The joy of life consists in the exercise of one’s energies, continual growth, constant change, the enjoyment of every new experience. To stop means simply to die. The eternal mistake of mankind is to set up an attainable ideal.” -Aleister Crowley
As we learn more and more about the Universe, we'd like to describe it as simply as possible. While we have thousands or even millions of chemical configurations, they arise from less than 100 different atoms. Atoms themselves are made up of protons, neutrons and electrons. The great hope of unification and for fans of elegance in general is that…
esiegel | October 27, 2016"Even if I stumble on to the absolute truth of any aspect of the universe, I will not realise my luck and instead will spend my life trying to find flaws in this understanding - such is the role of a scientist." -Brian Schmidt
Just a few days ago, a new paper was published in the journal Scientific Reports claiming that the evidence for acceleration from Type Ia supernovae was much flimsier than anyone gave it credit for. Rather than living up to the 5-sigma standard for scientific discovery, the authors claimed that there was only marginal, 3-sigma evidence for any sort of acceleration,…
esiegel | October 7, 2016“What is wild cannot be bought or sold, borrowed or copied. It is. Unmistakeable, unforgettable, unshamable, elemental as earth and ice, water, fire and air, a quintessence, pure spirit, resolving into no constituents.” -Jay Griffiths
At the earliest times, we can trace the history of our Universe back to an inflationary state, where the energy inherent to space itself caused a rapid, exponential expansion. At the latest (current) times, billions of years after inflation ended and the Big Bang occurred, dark energy has come to dominate the Universe’s expansion. These two states are very…
esiegel | September 15, 2016"Even if I stumble on to the absolute truth of any aspect of the universe, I will not realise my luck and instead will spend my life trying to find flaws in this understanding - such is the role of a scientist." -Brian Schmidt
The discovery of the accelerated expansion of the Universe -- and of dark energy behind it -- in 1998 was one of the biggest physics revolutions of our lifetime. By measuring these distant galaxies and how their distances and redshifts scale in the Universe, we were able to determine that despite everything we knew about matter and radiation, there was an additional…
esiegel | July 28, 2016"Another very good test some readers may want to look up... is the Casimir effect, where forces between metal plates in empty space are modified by the presence of virtual particles." -Gordon Kane
If you ask what the zero-point energy of space itself is, you can sum up all of the quantum fluctuations you can that arise in quantum field theory, and arrive at an absurd answer: 120 orders of magnitude greater than the observed. Yet if you assume that there’s an incredible cancellation and you get exactly zero, that removes the one thing our Universe needs to explain its expansion: dark energy.…
esiegel | July 23, 2016"We detect motion along this axis, but right now our data cannot state as strongly as we'd like whether the clusters are coming or going." -Alexander Kashlinsky
When dark energy was discovered, and the expansion of the Universe was shown to be accelerating, there was concurrently another puzzle that received much less attention: the problem of the Great Attractor. Galaxies appear to move due to both the Hubble expansion and the local gravitational field, but the gravity from the galaxies we saw didn’t account for all the motion.
The "flows" of galaxies mapped out with the mass field nearby.…
esiegel | July 13, 2016"If you're puzzled by what dark energy is, you're in good company." -Saul Perlmutter
The accelerated expansion of our Universe was one of the biggest surprise discoveries of all-time, and something that still lacks a good physical explanation. While many models of dark energy exist, it remains a completely phenomenological study: everything appears consistent with a cosmological constant, but nothing appears to be a good motivator for why the Universe should have one.
How energy density changes over time in a Universe dominated by matter (top), radiation (middle), and a cosmological constant…
gregladen | June 7, 2016Check out our detailed interview with the famous and amazing Ethan Siegel.
We talk about the history of understanding the universe, why you should believe in Dark Matter even though it is obviously fake, why exploring uranus can lead to the discovery of amazing things, and more.
esiegel | June 4, 2016"Until the 1990s, there were few reliable observations about movement at the scale of the entire universe, which is the only scale dark energy effects. So dark energy could not be seen until we could measure things very, very far away." -Adam Riess
Just thirty years ago, scientists argued over the value of the Hubble expansion rate, and what it meant for the age, history and fate of the Universe. Was the Universe expanding slowly (~55 km/s/Mpc), was it very old, and would it coast to infinity? Or was it expanding rapidly (~100 km/s/Mpc), was it young, and would it eventually recollapse?…
esiegel | May 19, 2016"We've known for a long time that the universe is expanding. But about 15 years ago, my colleagues and I discovered that it is expanding faster and faster. That is, the universe is accelerating, and that was not expected, but it is now attributed to this mysterious stuff called dark energy which seems to make up about 70 percent of the universe." -Adam Riess
The Universe has been said to be not only stranger than we imagine, but stranger than we can imagine. After the discovery of the expanding Universe, scientists considered that there was a great cosmic race from the moment of the Big Bang…