Einstein wondered what would happen if the Sun were to suddenly explode. Since the Sun is so far away that it takes light eight minutes to travel to Earth, we wouldn’t know about the explosion straight away. For eight glorious minutes we’d be completely oblivious to the terrible thing that was about to happen.

But what about gravity? The Earth moves in an ellipse around the Sun, due to the Sun’s gravity. If the Sun wasn’t there, it would move off in a straight line. Einstein’s puzzle was when that would happen: straight away, or after eight minutes? According to Newton’s theory, the Earth should know immediately that the Sun had disappeared. But Einstein said that couldn’t be right. Because, according to him, nothing can travel faster than the speed of light — not even the effects of gravity. […]

Before Einstein people thought of space as stage on which the laws of physics play out. We could throw in some stars or some planets and they would move around on this stage.

Einstein realised that space isn’t as passive as that. It is dynamic and it responds to what’s happening within it. If you put something heavy in space — let’s say a planet like Earth — then space around it gives a little. The presence of the planet causes a small dent in space (and in fact, in time as well). When something else moves close to the planet — say the Moon — it feels this dent in space and rolls around the planet like a marble rolling in a bowl. This is what we call gravity. […] Stars and planets move, causing space to bend in their wake, causing other stars and planets to move, causing space to bend in their wake. And so on. This is Einstein’s great insight. Gravity is the manifestation of the curvature of space and time.

{ Plus Magazine | Part One | Part Two }

Our best theories of physics imply we shouldn’t be here. The Big Bang ought to have produced equal amounts of matter and antimatter particles, which would almost immediately annihilate each other, leaving nothing but light.

So the reality that we are here – and there seems to be very little antimatter around – is one of the biggest unsolved mysteries in physics.

In 2001, Tanmay Vachaspati from Arizona State University offered a purely theoretical solution. Even if matter and antimatter were created in equal amounts, he suggested that as they annihilated each other, they would have briefly created monopoles and antimonopoles – hypothetical particles with just one magnetic pole, north or south.

As the monopoles and antimonopoles in turn annihilated each other, they would produce matter and antimatter. But because of a quirk in nature called CP violation, that process would be biased towards matter, leaving the matter-filled world we see today.

If that happened, Vachaspati showed that there should be a sign of it today: twisted magnetic fields permeating the universe. […] So Vachaspati and his colleagues went looking for them in data from NASA’s Fermi Gamma ray Space Telescope.

{ New Scientist | Continue reading }

related { Rogue antimatter found in thunderclouds }

All galaxies are thought to have supermassive black holes at their center. These start out small—with masses equivalent to between 100 and 100,000 suns—and build up over time by consuming the gas, dust, and stars around them or by merging with other black holes to reach sizes measured in millions or billions of solar masses. Such binge eating usually takes billions of years, but a team of astronomers was stunned to discover what is, in galactic terms, a monstrous baby: a gigantic black hole of 12 billion solar masses in a barely newborn galaxy, just 875 million years after the big bang.

{ Science | Continue reading }

No Big Bang? Quantum equation predicts universe has no beginning

The widely accepted age of the universe, as estimated by general relativity, is 13.8 billion years. In the beginning, everything in existence is thought to have occupied a single infinitely dense point, or singularity. Only after this point began to expand in a “Big Bang” did the universe officially begin.

Although the Big Bang singularity arises directly and unavoidably from the mathematics of general relativity, some scientists see it as problematic because the math can explain only what happened immediately after—not at or before—the singularity.

{ Phys.org | Continue reading }

Hilbert managed to build a hotel with an infinite number of rooms, all of which are occupied.

Suppose a new guest arrives and wishes to be accommodated in the hotel. Because the hotel has an infinite number of, we can move any guest occupying any room n to room n+1 (the occupant of room 1 moves to room 2, room 2 to room 3, and so on), then fit the newcomer into room 1.

Now suppose an infinite number of new guests arrives: just move any occupant of room n to room 2n (room 1 to room 2, room 2 to room 4, room 3 to room 6, and so on), and all the odd-numbered rooms (which are countably infinite) will be free for the new guests.

{ Wikipedia | Continue reading }

A team of scientists in the UK claims they’ve found evidence for alien life coming to Earth. According to their paper, published in the Journal of Cosmology (more on that in a moment) they lofted a balloon to a height of 22-27 kilometers (13-17 miles). When they retrieved it, they found a single particle that appears to be part of a diatom, a microscopic plant. This, they claim, is evidence of life coming from space. […]

The team publishing this paper includes […] a man who has claimed, time and again, to have found diatoms in meteorites. However, his previous claims have been less than convincing: The methodology was sloppy, the conclusions were not at all supported by the evidence, and heck, he hadn’t even established that the rocks they found were in fact meteorites. He also has a history of seeing life from space everywhere based on pretty thin evidence.

Moreover, this team published their results in the Journal of Cosmology, an online journal that doesn’t have the most discerning track record with science.

{ Slate | Continue reading }

The visible universe—including Earth, the sun, other stars, and galaxies—is made of protons, neutrons, and electrons bundled together into atoms. Perhaps one of the most surprising discoveries of the 20th century was that this ordinary, or baryonic, matter makes up less than 5 percent of the mass of the universe.

The rest of the universe appears to be made of a mysterious, invisible substance called dark matter (25 percent) and a force that repels gravity known as dark energy (70 percent).

Scientists have not yet observed dark matter directly. It doesn’t interact with baryonic matter and it’s completely invisible to light and other forms of electromagnetic radiation, making dark matter impossible to detect with current instruments. […]

Dark energy is even more mysterious, and its discovery in the 1990s was a complete shock to scientists. Previously, physicists had assumed that the attractive force of gravity would slow down the expansion of the universe over time. But when two independent teams tried to measure the rate of deceleration, they found that the expansion was actually speeding up. One scientist likened the finding to throwing a set of keys up in the air expecting them to fall back down-only to see them fly straight up toward the ceiling.

Scientists now think that the accelerated expansion of the universe is driven by a kind of repulsive force generated by quantum fluctuations in otherwise “empty” space. What’s more, the force seems to be growing stronger as the universe expands. For lack of a better name, scientists call this mysterious force dark energy.

{ National Geographic | Continue reading }

A day on the planet Venus is longer than a year on the planet Venus.

{ Discover | Continue reading }

Alien abduction insurance is an insurance policy issued against alien abduction.

The insurance policy is redeemed if the insured person is abducted by aliens.

The very first company to offer UFO abduction insurance was the St. Lawrence Agency in Altamonte Springs, Florida. The company says that it has paid out at least two claims.

The company pays the claimant $1 per year until their death or for 1 million years, whichever comes first. Over 20,000 people have purchased the insurance.

{ Wikipedia | Continue reading }

UFO reports have been evaluated in terms of the supposed reliability of eyewitness accounts and questionable photographic evidence. The constraints that interstellar distances, time and the conservation of energy impose on interstellar space travel for these supposed alien craft seem never to be considered by UFO proponents. Since they do provide descriptions of spacecraft of circular disks, cylinders and triangles that move strangely and rapidly and vary in size from 50 feet in diameter to 300 feet long, I undertake here to apply these constraints to the design of a hypothetical spacecraft in order to determine the feasibility of such craft and their use for interstellar travel. As a physicist and astronomer I think it important to consider not just the accounts of alien contact, but the physics of such a possibility as well.

For my model I have chosen a spacecraft with a crew of six that will leave its planet for a planet in the habitable zone of a star 10 light years away. It will be accelerated at a rate of 10 m/s² (10 meters per second squared) to a velocity of 0.5 times the velocity of light (0.5c, where c is the velocity of light). The time for it to reach this velocity is given by this equation:

t = v/a = 1.5×10⁸/10 = 3.06×10⁷s = 174 days

(a = acceleration in meters/second squared; v = velocity in meters/second; s = time seconds)

This is remarkably short compared to the nonrelativistic time of 20 years for the trip to the destination star. I have chosen 0.5c to minimize the relativistic mass increase of the spacecraft and to minimize travel time. The acceleration rate is approximately equal to the gravity the crew would experience on an earth-like home planet.

The spacecraft would be constructed in orbit from components delivered by shuttles. It would include, in addition to engines and fuel, an internal power supply for all the operational systems as well as life support systems and sustenance for the crew. For a 20-year trip this would necessarily be a small nuclear reactor. A mechanism for rotating the crew’s quarters to provide artificial gravity would be essential. I have chosen a live crew rather than robots or androids because all of the alien encounter and abduction stories indicate their presence. A shuttle for transporting the crew to the surface of the destination planet would also have to be on board.

Our current space shuttles have an unloaded mass of 10⁵ kg. Consequently, considering all of the requirements, a mass of 10⁷ kg is not unreasonable for our model. The kinetic energy of the spacecraft, defined as the energy any object has by virtue of its motion, at 0.5c is

E = ½mv2 = 0.5×10⁷×2.25×10¹⁶ = 1.13×10²³ joules

(m is the mass of the spacecraft and v is the velocity equal to 0.5c).

This is the energy that must be supplied by engine thrust to reach 0.5c

The only source that can supply energy of this magnitude is thermonuclear fusion. […] This energy would be expended over the 174 days of acceleration and is equal to 1.8 megatons per second during acceleration. […] For propulsion of the hypothetical spacecraft the blast energy would have to be converted, with near 100% efficiency, to a constrained unidirectional particle beam with thrust pulses of 1.8 megatons per second for 174 days. For a round trip to a star 10 light years distant this rate of energy expenditure would be needed for slowing down at the destination, leaving, and slowing down again when returning to the home planet after a 40 year expedition.

A lesser source than thermonuclear fusion would be inadequate to provide the required energy for traveling at 0.5c. A lower velocity would mean travel times of hundreds to thousands of years. A lower acceleration rate would greatly increase the time to reach the desired velocity. […]

There is no possible material construction that can constrain and direct the thermal and blast energy of the nuclear fusion rate required for interstellar travel. Consequently, I conclude that alien spacecraft cannot exist.

{ Skeptic | Continue reading }

Any spacecraft, whether from present or future technology, would have a significant inertial mass. Ten thousand years from now conservation of energy will apply anywhere in the galaxy as well as it does today. […]

In point of fact we do have proof of the effects of two megaton unconstrained nuclear fusion reactions, and because of the maximum cohesive force that electrons can create between protons no substance will remain solid above 5000ºC.

{ Skeptic | Continue reading }

The notion of panspermia – the transferral of viable organisms between planets, and even between star systems, seems to be getting a bit more attention these days. […]

There is no doubt that planetary surface material is continually being shipped around between rocky planets and moons in our solar system. Ejected by high energy asteroid or comet impacts, chunks of stuff follow a range of orbital trajectories that result in both eventual return to their origins or transferral to the surfaces of other worlds. Increasing evidence suggests that a variety of (typically microbial) organisms could be carried along, surviving both the extremes of pressure and acceleration, as well as exposure to thousands to millions of years of interplanetary space. They need not do this in stasis, tucked well inside the interstices of rock and ice it’s not inconceivable that microbes could be passengers in the natural equivalent of the generation ships of science fiction.

It means that there is a real possibility for life to both cross-infect, and even to be ‘seeded’ from planet or moon to planet or moon. […] Enthusiasts for panspermia go further, and have been known to invoke these mechanisms for galaxy-wide dispersal of life – taking one rare occurrence of life and spreading it across the stars. […]

There is a factor about large-scale panspermia that to my knowledge is rarely considered, and that is natural selection. […] The sequence of events involved in panspermia will weed out all but the toughest or most serendipitously suited organisms. So, let’s suppose that galactic panspermia has really been going on for the past ten billion years or so – what do we end up with?

{ Scientific American | Continue reading }

photo { Adam Kremer }

If one day is not exactly 24hrs and is in fact 23hr 56 mins, shouldn’t the error add up, and shouldn’t we see 12AM becoming noon at some point in time?

You’re right that a “sidereal” day is about 23 hours, 56 minutes, 4 seconds. But this is not a day in the everyday sense.

A sidereal day is how long it takes the earth (on average) to make one rotation relative to the faraway stars and other galaxies in the sky.

If you find a star that is directly above you at midnight one night, the same star will be directly above you again at 11:56:04 p.m. the next evening.

Similarly, if you were sitting on the star Proxima Centauri looking through a powerful telescope at earth, you would see Toledo, Ohio, go by every 23 hours, 56 minutes, and 4 seconds.

However, we don’t keep time by the faraway stars — we measure time by a much closer star, the sun! And we are actually in orbit around the sun, orbiting in the same direction that the earth is spinning on its own axis. From our perspective, the sun goes a little slower in the sky because we are also orbiting around it.

How fast are we orbiting around the sun? We make one full orbit every year, or roughly 366.25 sidereal days.

So after a year, the faraway stars will have done 366.25 rotations around the earth, but the sun will only have done 365.25 rotations. We “lose” a sunset because of the complete orbit. (The extra quarter day is why we need a leap year every four years.)

So there are 365.25 “mean solar days” in 366.25 “sidereal” days. How long is a “mean solar day”? Let’s do the math: One sidereal day is 23 hours, 56 minutes, 4 seconds, or 86164 seconds. Multiply this by 366.25 sidereal days in a year, and you get 31557565 seconds. Divide by 365.25 solar days, and we get that a solar day is…. 86,400 seconds. That’s 24 hours exactly!

{ Quora | Continue reading }

If aliens come, we’re probably toast.

Whoever takes the trouble to come visit us is probably a more aggressive personality. And if they have the technology to come here, the idea that we can take them on is like Napoleon taking on U.S. Air Force. We’re not going to be able to defend ourselves very well.

{ Seth Shostak/IEEE | Continue reading }

related { Does the Pentagon have the right weapons to fight off an alien invasion? }

Sometime within the next 5 years, the Voyager 1 space craft is expected to reach interstellar space. It will be the first man made object to cross the heliosphere, which is the final stop in our solar system.

After being launched in 1977, Voyager 1 was the first probe to visit many of the outer planets. It has sent back countless original images from space, almost all of which have been released to the public. Although NASA does sell images, and many appear in copyrighted works (such as books); NASA is very good about releasing information into the public domain, almost all scientifically significant information from space is given to the public.

Voyager 1, famously contained a gold phonographic record. The record was filled with iconic sights, images, and sounds from earth, and the prevailing message, “we come in peace”. We think. Even though any alien that can figure out how to play a phonographic record, will have certainly already have received fox news, the contents of the actual gold record are not public domain.

The disc was comprised by a man named Carl Sagan, and it contained many pieces of art, songs, and images, that are all copyrighted. Sagan had to secure the rights to include these items separately, at great expense. The special alien license does not allow the right to free copy and distribution to educators. In fact, it is unclear if an original copy of the entire disc still exists on earth at all.

{ Active Politic | Continue reading }

Each Voyager space probe carries a gold-plated audio-visual disc in the event that either spacecraft is ever found by intelligent life-forms from other planetary systems. The discs carry photos of the Earth and its lifeforms, a range of scientific information, spoken greetings from the people (e.g. the Secretary-General of the United Nations and the President of the United States, and the children of the Planet Earth) and a medley, “Sounds of Earth,” that includes the sounds of whales, a baby crying, waves breaking on a shore, and a variety of music.

{ Wikipedia | Continue reading }

photo { featured in the Voyager Golden Record: Demonstration of licking, eating and drinking }

Could mirror universes or parallel worlds account for dark matter — the ‘missing’ matter in the Universe? In what seems to be mixing of science and science fiction, a new paper by a team of theoretical physicists hypothesizes the existence of mirror particles as a possible candidate for dark matter. An anomaly observed in the behavior of ordinary particles that appear to oscillate in and out of existence could be from a “hypothetical parallel world consisting of mirror particles,” says a press release from Springer. “Each neutron would have the ability to transition into its invisible mirror twin, and back, oscillating from one world to the other.”

{ Universe Today | Continue reading }

photo { Aaron Fowler }

{ On Tuesday/Wednesday June 5/6, Earth will have the best seat — the only seat — for a great show: the Transit of Venus across the face of the Sun. | Discover | full story }

In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles.

For example, a positron (the antiparticle of the electron) and an antiproton can form an antihydrogen atom in the same way that an electron and a proton form a “normal matter” hydrogen atom.

Furthermore, mixing matter and antimatter can lead to the annihilation of both, in the same way that mixing antiparticles and particles does, thus giving rise to high-energy photons (gamma rays) or other particle–antiparticle pairs.

The result of antimatter meeting matter is an explosion.

There is considerable speculation as to why the observable universe is apparently composed almost entirely of matter (as opposed to a mixture of matter and antimatter), whether there exist other places that are almost entirely composed of antimatter instead, and what sorts of technology might be possible if antimatter could be harnessed. At this time, the apparent asymmetry of matter and antimatter in the visible universe is one of the greatest unsolved problems in physics.

{ Wikipedia | Continue reading }

An international collaboration of scientists has reported in landmark detail the decay process of a subatomic particle called a kaon – information that may help answer fundamental questions about how the universe began. The research used breakthrough techniques on some of the world’s fastest supercomputers to expand on a 1964 Nobel Prize-winning experiment. […] “This calculation brings us closer to answering fundamental questions about how matter formed in the early universe and why we, and everything else we observe today, are made of matter and not anti-matter,” says Thomas Blum, associate professor of physics at the University of Connecticut, a co-author of the paper.

{ DailyGalaxy | Continue reading }

photo { Lee Kwang-Ho }

A new company backed by two Google Inc. billionaires, film director James Cameron and other space exploration proponents is aiming high in the hunt for natural resources—with mining asteroids the possible target. (…)

The possibility of extracting raw materials such as iron and nickel from asteroids has been discussed for decades, but the cost, scientific expertise and technical prowess of fulfilling such as feat have remained an obstacle. NASA experts have projected it could cost tens of billions of dollars and take well over a decade to land astronauts on an asteroid. (…)

Earlier this month, a study by NASA scientists concluded that, for a cost of $2.6 billion, humans could use robotic spacecraft to capture a 500-ton asteroid seven meters in diameter and bring it into orbit around the moon so that it could be explored and mined. The spacecraft, using a 40-kilowatt solar-electric propulsion system, would have a flight time of between six and 10 years, and humans could accomplish this task by around 2025.

{ WSJ | Continue reading | Asteroid Retrieval Feasibility Study | PDF }

{ New analysis of 36-year-old data, resuscitated from printouts, shows NASA found life on Mars, an international team of mathematicians and scientists conclude in a paper published this week. }

One of the great challenges in cosmology is understanding the nature of the universe’s so-called missing mass.

Astronomers have long known that galaxies are held together by gravity, a force that depends on the amount of mass a galaxy contains. Galaxies also spin, generating a force that tends to cause this mass to fly apart.

The galaxies astronomers can see are not being torn apart as they rotate, presumably because they are generating enough gravity to prevent this.

But that raises a conundrum. Astronomers can see how much visible mass there is in a galaxy and when they add it all up, there isn’t anywhere enough for the required amount of gravity.  So something else must be generating this force. 

One idea is that gravity is stronger on the galactic scale and so naturally provides the extra force to glue galaxies together.

Another is that the galaxies must be filled with matter that astronomers can’t see, the so-called dark matter.

{ The Physics arXiv Blog | Continue reading }

photo { Bela Borsodi }

One by one, pillars of classical logic have fallen by the wayside as science progressed in the 20th century, from Einstein’s realization that measurements of space and time were not absolute but observer-dependent, to quantum mechanics, which not only put fundamental limits on what we can empirically know but also demonstrated that elementary particles and the atoms they form are doing a million seemingly impossible things at once. (…)

Eighty-seven years ago, as far as we knew, the universe consisted of a single galaxy, our Milky Way, surrounded by an eternal, static, empty void. Now we know that there are more than 100 billion galaxies in the observable universe. (…)

Combining the ideas of general relativity and quantum mechanics, we can understand how it is possible that the entire universe, matter, radiation and even space itself could arise spontaneously out of nothing, without explicit divine intervention. (…)

Perhaps most remarkable of all, not only is it now plausible, in a scientific sense, that our universe came from nothing, if we ask what properties a universe created from nothing would have, it appears that these properties resemble precisely the universe we live in.

{ Lawrence M. Krauss/LA Times | Continue reading }

artwork { Ellsworth Kelly, White curve I (black curve I), 1973 }