“Since its discovery in 1998, the accelerated expansion has lacked a compelling, simple explanation that didn’t hypothesize a completely new set of forces, properties or interactions. If you wanted a scalar field — a quintessence model — it had to be finely tuned. But in a very clever paper just submitted yesterday by Fergus Simpson, Raul Jimenez, Carlos Pena-Garay, and Licia Verde, they note that if a generic scalar field couples to the neutrinos we have in our Universe, that fine-tuning goes away, and that scalar field will automatically begin behaving as a cosmological constant: as energy inherent to space itself.”
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. Until now, that is! In a new paper by Fergus Simpson, Raul Jimenez, Carlos Pena-Garay and Licia Verde, they note that any generic scalar field that couples to the neutrino sector would dynamically and stably give rise to a type of dark energy that’s indistinguishable from what we’ve observed. The huge advance is that this scenario doesn’t require any fine-tuning, thanks to this dark energy arising from neutrinos “freezing,” or becoming non-relativistic. In addition, there are experimental signatures to look for to confirm it, too, in the form of neutrinoless double-beta decay!
Benjamin died on September 7th, 1936 in Hobart zoo. It is believed that he died out of neglect, as he was locked out of his shelter and was exposed to the searing hot sun and freezing cold night of Tasmania.
The Thylacine was one of the last large marsupials left on Australia (the other being the Kangaroo) after a great extinction event occurred around 40 thousand years ago. This extinction event, caused mainly by the arrival of humans, wiped out 90% of Australia’s terrestrial vertebrates, including the famous Megafauna.
The Thylacine was around 15-30kg (33-66lbs), were carnivorous, and had numerous similarities to other species like dogs, despite not being related and purely by chance, in a phenomenon known as convergent evolution (just like the ability to fly of bats and birds, despite following different evolutionary paths). Not only that, they could open their jaws up to 120 degrees, could hop around on two legs like a kangaroo, and both males and females had pouches.
Lastly in a cruel twist, the Tasmanian government decided to protect the Thylacine - just 59 days before the last one died, in a very notable case case of “Too little too late”. To date, many biologists believe that there are still Thylacine roaming the wild plains of Australia.
Underwater explosions are incredibly dangerous and destructive, and this animation shows you why. What you see here are three balloons, each half-filled with water and half with air. A small explosive has been set off next to them in a pool. In air, the immense energy of an explosion actually doesn’t propagate all that far because much of it gets expended in compressing the air. Water, on the other hand, is incompressible, so that explosive energy just keeps propagating. For squishy, partially air-filled things like us humans or these balloons, that explosion’s force transmits into us with nearly its full effect, causing expansion and contraction of anything compressible inside us as our interior and exterior pressures try to equalize. The results can be devastating. To see the equivalent experiment in air, check out Mark Rober’s full video on how to survive a grenade blast. (Image credit: M. Rober, source)
Infographic about Planet 9, the required planet to explain the trajectory of six of the most distand known Kuiper Belt Objects.
Source: http://imgur.com/S5faizX
Can you explain in a simple (???) way gravitational waves? please? do you know any books about it?
Sure!
According to Einstein’s General Theory of Relativity, what we think of as "empty space” isn’t nothing. Instead, space is more like a fabric that can be stretched, squashed, bent and shaped, and all matter and energy cause space to bend around them. The more mass or energy something has, the greater the bending of space around it it causes, a bit like heavier and lighter balls on a rubber sheet:
(Source - Note that this picture is a 2D analogy, and space is actually 3D! The bending of space isn’t something we can easily visualise, so we have to use analogies like the “balls on a rubber sheet” analogy - as long as we recognise their shortcomings!)
Let’s imagine the Sun is a bowling ball dropped onto a rubber sheet, creating a huge dent in space. And now let’s roll a marble - Earth - onto that sheet too. IF the marble is rolling too slowly, it will fall into the dent and roll around a few times, spiralling in and eventually colliding with the ball. If the marble is rolling too quickly, its path will be bent, but it will escape. If it’s rolling at a certain speed, however, the marble will roll around the bowling ball and go into orbit around it. (Here’s another shortcoming of the rubber sheet analogy - real rubber sheets have friction, so the marble would eventually slow down and roll in towards the bowling ball. Space, however, has no friction, so the Earth can stay in orbit around the Sun for a long time.) In other words, this bending of space is what we refer to as gravity!
In Newton’s view of gravity, Earth would naturally follow a straight line through space, but its path would be bent towards the Sun by a mysterious pulling force. That force holds the planets in orbit around the Sun and pulls apples to Earth, but Newton couldn’t explain why - a mysterious influence that spread out through space, called the gravitational field, somehow caused bodies to attract one another. Einstein explained that massive objects curve the space around them. Earth would also naturally follow a straight line through space, but the space itself is curved, forcing Earth to follow a curved path - it’s a bit like trying to walk in a straight line along a hill. Try as you might, your path will have to bend to follow the contours of the landscape. According to Einstein, gravity isn’t really a “force” as such but an effect of this bending of space. Matter and energy tell space how to bend; space tells matter and energy how to move. That’s all gravity is. The gravitational field isn’t some mysterious entity in space - the gravitational field is the space itself! Here’s a nice little video to help you visualise all this:
(I’m oversimplifying a little, btw, saying that gravity is the bending of “space.” In Einstein’s theory, the three dimensions of space are unified with time into one four-dimensional fabric, the space-time continuum. So gravity isn’t just the bending of space, but the warping of time too - you can’t change one without changing the other! Gravity actually slows time down, so you would age slightly faster in space than you do at Earth’s surface. The difference is incredibly tiny, but measurable - time passes more quickly for the GPS satellites than it does for us here on Earth, and what the clock of a GPS satellite would measure as “one day” is about 38 microseconds shorter than what we measure as “one day.” That doesn’t sound like a big difference, but engineers have to take it into account when designing GPS systems - if they didn’t account for this, your GPS location would drift by as much as 10 kilometres per day! So this isn’t just some abstract theory - this is a real effect that’s already important for technology you probably use every day.)
General Relativity has now been through many, many tests and has passed every one with flying colours, and all of its predictions had been verified by the beginning of 2016 except one - gravitational waves.
What would happen if we could somehow destroy the Sun? Newton believed that there was a mysterious gravitational connection between the Sun and Earth, holding Earth in its orbit, that would instantly be broken if the Sun was destroyed. Earth would instantly fly out of its orbit in a straight line. Einstein, however, didn’t like this - his Special Theory of Relativity (which he put out 10 years before the General Theory) says that no information could ever travel faster than light. It takes about 8 minutes for the Sun’s light to reach us, so how could Earth fly out of its orbit instantly? That would let us know the Sun had been destroyed 8 minutes before the light from the Sun’s destruction reached us. Einstein wasn’t comfortable with this.
Thankfully, General Relativity resolves the paradox - if you got rid of the Sun, Earth would still stay in its orbit for a while, because the space-time around the Sun would still be curved. Meanwhile, at the place where the Sun was, space-time would spring back to its original flat state, and that would ripple through the surrounding space-time as everything adjusted back to where it was. That ripple - a gravitational wave - would spread out through space at the speed of light, so the space around Earth would stay curved and Earth would remain in its orbit until the same time the light from the Sun’s destruction passed us - at which point the gravitational wave would ripple through the space around Earth and restore it back to its original flat state, and Earth would finally leave its orbit.
Of course, in reality, stars don’t just disappear. But the gravitational environment does change. Stars move around, and the fabric of space-time also moves with them. Stars explode. Black holes and neutron stars form, putting huge dents in space-time, and sometimes they collide. All these events are a bit like changing the environment in a still pond - stars and planets gently orbiting are like ducks gently gliding through the pond, creating gentle ripples as they disturb its surface - and black hole collisions are more like throwing a rock into the pond and sending out massive waves. Almost everything in our universe produces gravitational waves, but most of the time, they’re too tiny to detect. (That’s why I said in real space the Earth can orbit the Sun for “a long time,” and not “forever.” Earth is constantly sending out very faint gravitational waves as it rolls around the Sun and moves through the fabric of space-time. Those waves are too small to detect, but they very, very slowly sap Earth’s energy and cause it to very, very slowly spiral in to the Sun. In reality, that would take unimaginable trillions upon trillions of years, and Earth will probably be destroyed by the dying Sun long before that! Even if Earth manages to survive that, it’s more likely to be pulled out of orbit by an incredibly rare passing star or knocked out by unpredictable gravitational tugs from the other planets or something before it spirals into the Sun. Orbits are stable for a very, very, very, very long time.) More intense sources of gravity than our puny Earth and Sun, however - things like neutron stars and black holes - can generate detectable gravitational waves.
Our first indirect evidence of gravitational waves came in 1984, when the American astronomers Russel A. Hulse and Joseph A. Taylor discovered a binary neutron star system - two intense sources of gravity orbiting each other very rapidly. As they orbited each other, they sent out huge gravitational ripples - a bit like stirring up that duck pond with two oars whirling round and round - and lost energy by a detectable amount. Hulse and Taylor found that their orbital period slowed down by about 75 milliseconds per year - short, but detectable! That slowing exactly matched the predictions of gravitational wave theory and got its discoverers the Nobel Prize for Physics in 1993.
(Source)
But gravitational waves weren’t directly observed until 2015 (and confirmed until this year) by a detector named LIGO (the Laser Interferometer Gravitational wave Observatory). All LIGO is is basically two beams of laser light travelling between two pairs of mirrors oriented at right angles to each other, like this, so you can measure how space-time is stretched in one direction and squashed in the other by a passing gravitational wave by recording how long it takes the light to travel from one mirror to the other*:
(Source for both images: http://phys.org/news/2016-02-ligo.html)
LIGO’s two “arms” (the two beams of light) are each 4 kilometres long, and a gravitational wave passing through the detector stretches or squashes each of the “arms” by a ridiculously small amount - the ones LIGO actually found stretched and about 1/10,000th the width of a proton. As you can imagine, the LIGO physicists had to account for many, many different effects that shook the detector too. But gravitational waves distort the two beams in a predictable way that would make that distortion stand out from ordinary passing trucks or distant earthquakes, and by February 11th, 2016, the LIGO physicists were confident enough that they really had detected a faint ripple in space-time passing through their detector. The signal was consistent with a gravitational wave from two black holes in orbit around each other, spiralling in to one another.
(Source)
This is exciting for two reasons:1) It confirms the last outstanding prediction of General Relativity, and2) It opens up a whole new field of astronomy! Every so often astronomy is revolutionised by the discovery of new things we can look at from space. Originally all we could detect was the visible light that we could see with our eyes and telescopes. But soon we learned to build radio telescopes, and that opened up a whole new world to us - we could see phenomena that were invisible in ordinary light. With space telescopes we could see the sky in gamma rays, x-rays, ultraviolet and infra-red light as well. Now we could see the explosions of distant stars halfway across the observable Universe, look at clouds of gas and dust too cool to shine in visible light, and peer through other dark clouds to see stars forming inside. We also found particles we could see coming from space, too - neutrinos from the Sun and from supernovae, and cosmic rays. These opened up other windows on the Universe. And now we have gravitational waves - yet another new way of “seeing.” Gravitational wave astronomy will let us study some of the most puzzling events in the Universe, like colliding neutron stars, or black holes falling into other black holes - events we’ve never been able to see before.
So I hope that helps, Anon!
As for books, the problem is gravitational waves were detected so recently I don’t know of any books that have come out since then on the subject, so everything will be out of date. However, the basic physics has stayed the same since Einstein first predicted them, so any good popular book on general relativity (Spacewarps by John Gribbin, The Fabric of the Cosmos by Brian Greene and Travelling At the Speed of Thought: Einstein and the Quest for Gravitational Waves by Daniel Kennefick are good examples) should give you some good insight - just replace phrases like “if we detect gravitational waves” with “when we detected gravitational waves!”
(*Yes, yes, I know LIGO isn’t actually measuring the time taken for light to travel down each “arm,” but the interference of the laser beams. Still, that interference allows us to infer the travel time for the light, so I’m simplifying.)
Asteroid Watch logo. August 5, 2019
Near Earth Asteroid
An asteroid 570 meters in diameter is expected to approach 8 million kilometers from our planet on August 10. The situation is of no concern to NASA specialists, who stress the large number of similar celestial objects that are spotted each year near the Earth. The space agency says it fears more those who are not listed.
Artist’s impression of 2006 QQ23 asteroid
According to NASA, an asteroid the size of a skyscraper will pass near the Earth on Saturday, August 10. Called “2006 QQ23”, the celestial object is approximately 570 meters in diameter and its trajectory will place it at a distance of 8 million kilometers from our planet, closer to home, says CNN. A “more or less benign” situation for experts from the American Space Agency. This asteroid is of a “moderate size” Lindley Johnson of NASA’s Global Coordinating Office for Defense says the asteroid is “of moderate size” and explains that half a dozen similar-sized aerolites are approaching each year. Not to mention that the solar system includes nearly 900 of a volume greater than that which advances towards the Earth. The specialists are therefore reassuring.
2006 QQ23 orbit
They explain having already studied the movements of “2006 QQ23” since the year 1901 and until 2200. Because a possible impact between the Earth and a foreign body of this size would cause significant damage over a large area . Even if this scenario occurred, NASA would then be able to launch a space mission to deflect the celestial object. When it comes to asteroids, “it’s the ones we do not know about that worry us,” says Kelly Fast, also a member of the Coordination Office. Related article: Asteroid’s surprise close approach illustrates need for more eyes on the sky https://orbiterchspacenews.blogspot.com/2019/08/asteroids-surprise-close-approach.html Additional information: Asteroid Watch: For more information about asteroids and near-Earth objects, visit: http://www.jpl.nasa.gov/asteroidwatch and http://www.nasa.gov/asteroid . Updates about near-Earth objects are also available by following AsteroidWatch on Twitter at http://www.twitter.com/asteroidwatch . Near-Earth Object Program Office: http://neo.jpl.nasa.gov/ Images, Text, Credits: AFP/NASA/ESA/Orbiter.ch Aerospace/Roland Berga. Best regards, Orbiter.ch Full article
The solar eclipse that occurred in Chile on July 2, 2019 photographed by Dan Marker-Moore. Great job!
Via Colossal
A baobab tree and the central band of the Milky Way galaxy in the village of Antsiraraka in Madagscar, July 2010.
Credit: Florian Breuer
If someone is attractive and charming, you’re more likely to assume they’re intelligent and hard working- even if they’re not.
Known as the ‘Halo Effect’, it’s a theory that our generalized judgements of people can bleed over into the more specific judgements we make about them. Studies show that even though we understand the Halo Effect intellectually, it’s almost impossible for us to recognize when it’s actually happening.
(Source, Source 2)
This is a studyblr for everyone have some passion for science, especially astronomy and biology
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