Andromeda is headed our way at about seventy five miles per second.
In about three or four billion years the Andromeda and Milky Way galaxies will collide. The result, if anybody is around to see it, will be beautiful. The two galaxies will pass through each other first. There is so much empty space, and the distance between stars so great, that it’s extremely unlikely that any stars will actually collide. But dust and gas clouds will, and that means that the rate of star creation will be greatly boosted.
Additionally, supernovae (which currently happen within either galaxy every 50 years or so) will likely start happening about once a year with some of them being close enough to outshine all the rest of the stars as seen from Earth.
Having passed through on a grazing course, Andromeda will retreat for a while, and then come back for a head-on collision. This time, the super-massive black holes at the centers of the galaxies will pass close enough together to pull each other in and merge. Gravitational waves will fling many stars out of the galaxies into intergalactic space, and will pull many others closer to the core. There’s a good chance that our sun (which will be a bit bigger, but still exist) along with its planets (Earth will still be there, but it will be parched and lifeless) will get pulled towards the center of the combined galaxies and then flung outward. (There’s a smaller chance that the flinging could send us right into one of the black holes.)
Our night sky right now is beautiful. But compared to what will be visible during these goings-on, it’s downright dull. The sky will be filled with so many stars that the night will no longer be dark. Gas clouds will glow brightly and in many colors. If we get close enough to the center, we’ll even be able to see massive gas jets shooting from the black holes in the core.
Shortly thereafter, the sun will finally expand to engulf the Earth bringing our planet to its final demise. But what an exit!!
(That article is about eight years old, but still accurate. The most substantive change to our knowledge since then is the confirmation in 2012 via Hubble data that the collision is, in fact, inevitable.)
Baby teeth appear around the ages of six months and three years and begin to be replaced at about six years of age.
Humans are born with the beginnings of permanent teeth under the gums below the baby teeth. Baby teeth guide the growth and development of the jawbones and of the permanent teeth. Losing baby teeth too early can result in jaw not developing correctly, and the permanent teeth coming in crooked or being overcrowded.
Different teeth handle food in different ways. Incisors (front teeth) are chisel-shaped, their sharp edges bite off relatively large pieces of food. The cuspids (canine teeth) are cone-shaped, and are used for grasping and tearing food. The bicuspids and molars have flattened surfaces and are used for grinding food.
photo credit: Stefan Schäfer
When it comes to protecting the Earth from potentially catastrophic asteroid collisions, NASA has finally offered a plan that doesn’t rely on getting additional budget: Prayer.
It may sound surprising to hear that kind of advice from an organization that many think of as a bastion of secular science, but it is actually a better plan than the next best which is to do nothing at all. With the tiny portion of our country’s budget that goes to NASA (half a penny from a tax dollar), it just isn’t realistic to do anything else. They keep looking and (depressingly) keep finding more and more rocks out there in this shooting gallery called home, but if they find one headed our way with enough mass and/or speed to kill us all, then there’s not a whole lot that they can do about it unless they catch it quite a lot earlier than they are likely to.
The only realistic solution is to fund NASA more robustly, and as much as we here at Science That (including most of our wonderful readers) support that idea, our lawmakers and many of their constituents don’t. So, if you don’t mind remaining helpless while the heavens throw rocks at you and try really hard to kill you, then feel free to just sit back and click the next link to some other thing on the internet and enjoy a day of surfing. On the other hand, if you’re the least bit irked that public safety takes such a backseat to so many other things, then write to your congresspeople and tell them that you’d like for them to please save the world. This is not a partisan issue – if an asteroid claims lives, it will not care who sits where. It will be an equal opportunity catastrophe.
One of my favorite sayings, which I heard from a very religious and very Irish aunt, was, “Pray for rain, but plant potatoes.” Whether prayer works or not, the time is here to plant potatoes by telling our leaders to stop waiting until it’s too late.
You know when you get that feeling in your knuckles, back, or neck and you just have to crack it? The action is often accompanied by a relatively loud popping sound that is sometimes met with awkward looks from passersby. Or, if you’re like me, it’s met with a scolding from your mother and a warning that you’ll cause damage to your bones by grinding them together.
It seems intuitive but what’s actually going on when you pop a joint? And is it dangerous? The short answer is we don’t know and… we don’t know. But we have some ideas.
The prevailing hypothesis involves something called synovial fluid and dissolved gases.
Synovial fluid exists within the joint capsule between two bones and acts as a lubricant. The fluid has within it dissolved gases, when you push a joint toward its limit the joint capsule is stretched and the dissolved gases are rapidly released from the synovial fluid causing a popping sound.
The joint can’t be popped again until the gasses are dissolved back into the synovial fluid, hence the delay in being able to pop a particular joint again.
While this is the leading explanation for most joint ‘cracking’ noises, popping noises can be generated via other means, if there is no delay in the ability to pop a joint it likely isn’t caused by the release of gas in the synovial fluid.
This leads us to our final question. Was Mom right about it being dangerous or harmful? The jury is still out on this one, results vary and are conflicting, some studies show no indication of harm or risk while others indicate that repetitive cracking may cause damage to surrounding tissues.
You’re probably in no real risk of severe damage. Know your body’s limits and when in doubt, consult a licensed physician.
P.S. I popped my knuckles about a dozen times while writing this. Am I alone? Did you crack your knuckles or neck while reading. Type up your thoughts with your newly limbered digits.
Everyone knows about the dazzling ring system of Saturn. The majestic gas giant’s elaborate system of rings makes Saturn a much loved target for observation through a telescope. What most people may not know is that Saturn has an even bigger, but very tenuous, ring—one that begins 6 million kilometers beyond the planet and extends outward another 12 million kilometers! Doing the math, we find that the diameter of this newly found ring is about 36 million kilometers. At a diameter of 116,464 kilometers, it would take 309 Saturns stacked across to fill the diameter of this ring. The ring is very thick as well—it would take about 20 Saturn diameters to match its thickness. If you could see it, the ring would span two full moons across the sky. The new ring is tilted at about 27° to the plane of the main ring system.
Another point of interest is that this ring orbits Saturn in a direction opposite that of the other rings and most of Saturn’s moons. This may explain why Saturn’s moon Iapetus has one dark side, as it is constantly slammed with dusty material from the ring. Orbiting in the direction of Saturn’s moon Phoebe and along the moon’s path, the origin of the gigantic ring may be from the moon itself due to collisions with other smaller bodies. Having a battered appearance, it is clear that Phoebe has lost a lot of its material. This material, along with debris from collisions with other objects, is likely what formed Saturn’s largest ring—the Phoebe ring.
The first time Saturn’s rings were discovered was in 1610 when Galileo Galilei pointed his telescope at the gas giant. Only back then, no one could conceive what planetary rings were, and he incorrectly guessed they were Saturn’s moons. In 1659, Christian Huygens solved the mystery—this was a ring system. Voyagers 1 and 2 provided a closer look at the rings in the 1980’s. The Cassini-Huygens spacecraft, launched in 1997 and arriving at the Saturn system in 2004, revealed the most detailed information about the system ever. But it was the Spitzer Space Telescope who discovered the new giant ring in 2009 with observations in the infrared.
Saturn’s main ring system is about one kilometer thick and 282,000 kilometers wide. The rings are relatively close together, except for the Cassini Division which spans about 4700 kilometers. Starting from the inner ring and working outwards, the main rings are known as C, B, and A, with the Cassini Division separating B and A. Within the A ring, there is yet another gap that is 325 kilometers wide—the Encke Gap. Less visible rings are the D ring (closest to the planet), and the F ring (beyond the A ring). Beyond the F ring are two even fainter rings called the G and E rings. The Roche Division, a 2600-kilometer-wide gap, separates rings A and F. There are several more gaps within the rings that are smaller, making this ring system very well defined and stunning to look at. Then, there is the Phoebe ring, visible in the infrared, inclined at 27° to the main ring system and circling in the opposite direction, far wider than the main ring system and lying far beyond it. While all the gas giants have rings, Saturn truly holds the most wondrous system of rings in the solar system.
Saturn’s Phoebe ring:
History of Saturn: http://huygensgcms.gsfc.nasa.gov/Shistory.htm
Saturn’s ring system:
Until recently, neurological studies involved implanting electrodes into specific regions of the brain. The activity of the neurons in contact with the electrodes was recorded, and correlated to the subject’s activity. Electrical stimulation can be used to fire neurons, but it covers a large area and can’t isolate specific neurons.
An ideal option is to have the ability to turn individual neurons on and off. To accomplish this, researchers turned to ion channels, which are specialized proteins, and depending on the type, either allow or block the movement of ions across a cell membrane (an example of an ion channel is rhodopsin, a light sensitive protein in the retina).
But how does one modify a neuron to include an ion channel? This requires engineering lentiviruses to carry the ion channel. The lentiviruses are inserted into specific neural regions, and the infection modifies the areas to include the ion channels.
Once the neurons include ion channels optical fibers are inserted into the modified neural regions. Specific light wave lengths are then can be used to turn the neurons on and off.
Although optogenetics is still in early stages, its potential has many exciting possibilities. Some applications include turning off compulsive behavior, restoring sight, curing Parkinson disease and epilepsy.
We have all heard the famous quotes “We are made of star stuff” from astronomer Carl Sagan and “We are not figuratively, but literally stardust” from astrophysicist Neil deGrasse Tyson. Now, let’s get into exactly what they mean, and how it is that we have come to be made from the stuff of stars.
Let’s begin with the two most common elements in the Universe: hydrogen, followed by helium. 13.8 billion years ago, the Big Bang gave rise to our Universe. The Big Bang created all the matter in the Universe after undergoing a series of events. The hydrogen nucleus is just a proton, so it was the first of the nuclei created, and the most abundant. Through nuclear reactions, hydrogen then formed helium nuclei. Very rarely, fusions led to the formation of lithium, and even less so, beryllium. This is pretty much all that was formed in the early Universe, because anything heavier requires more heat, and the Universe cooled quickly as it expanded with time. A point of interest is that all the hydrogen in the Universe today was formed when it was young—it is a relic of the Big Bang. Today, hydrogen and helium dominate the elements in the Universe at 98% by mass (about 73% hydrogen and 25% helium). The remaining 2% constitute the other elements.
The hydrogen produced in the early Universe then went into forming stars, stars that would fuse this hydrogen into heavier elements. Stars are like big nuclear fusion houses in which lighter elements are constantly being fused into heavier ones. A star begins by fusing hydrogen into helium. The lowest mass stars in the Universe run out to fuel once all their hydrogen has been fused into helium, leaving them with an inert helium white dwarf core. Medium sized stars like our Sun will fuse the helium into heavier elements like carbon and oxygen. Once all the helium is depleted, they are left with an inert carbon core and shed their layers in a planetary nebula, with a white dwarf remaining at the center.
Stars heavier than five solar masses are ones of particular interest—these are the stars that facilitate the formation of the heaviest atoms. Such stars will continue fusing carbon into even heavier elements. If a star is massive enough, it will go on fusing elements into nickel, which decays into iron, and become a red supergiant. Because it takes energy to fuse iron into heavier elements, iron is the end of the line for the star. At this point, the star will explode in a violent supernova that leaves behind either a neutron star or a black hole, depending on its mass. This explosion produces temperatures so high that it ignites nucleosynthesis again, producing elements as heavy as gold, platinum and silver, to name a few. Spewing elements the star once contained, and ones newly formed, the supernova essentially spreads out the necessary ingredients for life.
Elements spewed from supernovae enrich molecular clouds that condense under gravity, eventually forming stars, and possibly planets that orbit those stars. Such star systems will have all the ingredients required for life, thanks to stars fusing elements in their cores, and supernovae further fusing these elements into even heavier ones. On Earth, a few billion years combined with favorable conditions, the right distance from the Sun, and the required ingredients for life, resulted in a planet beaming with life. We can take “stardust” to be all atoms aside from hydrogen (which we know was exclusively formed during the Big Bang). Our bodies are composed of 60% water. Water is only about 11% hydrogen by mass. When looking at the rest of the stuff we are made of (which includes “stardust” and some hydrogen), we find that the human body is 93% stardust by mass—the remaining 7% is hydrogen, a relic of the big bang. In this way, we are all quite literally stardust, or star stuff (with a bit of Big Bang stuff).
Taking into account that this process is undergone everywhere in a universe as vast as the one in which we live, does it not follow that our universe may be beaming with life? The very stuff we are made of is spewed all over the universe, and becomes part of other molecular clouds that form star systems, systems that will be enriched will all the necessary ingredients for life… Life elsewhere seems almost inevitable, doesn’t it? I certainly think so.
When air moves against a boat’s sail, the momentum of the molecules in the air is imparted to the sail, causing the boat to move. Those molecules in the air have mass, and you multiply that mass by their velocity to determine how much momentum they possess.
That’s a simple example of classical Newtonian physics.
But we know that photons have no mass. If mass equals zero, then regardless of their velocity that multiplication works out to zero momentum. So how can a solar sail work?
If Isaac Newton’s classical model was entirely correct, then solar sails wouldn’t work. It’s Einstein’s relativity theories that fix it. As something accelerates (linearly for simplicity), it gains kinetic energy and its linear momentum increases. An actual particle of matter would have infinite mass and momentum if it got to light speed, which is why nothing with a rest mass can be accelerated to that speed.
Photons have no rest mass, though, and so don’t suffer from that problem.
The theory of relativity that people are most familiar with is E=mc², where E stands for Energy, m stands for mass, and c stands for the speed of light in a vacuum.
But that’s a simplified version that doesn’t take momentum into consideration.
The more correct (and slightly less able to fit on a postage stamp) formula is E²-p²c²=m²c⁴ where p is momentum.
With photons, m=0 since they have no mass. Since m=0, the equation reduces to E²-p²c²=0.
Solving for p, we get p=E/c.
Therefore, the momentum of a particle is equal to its energy (frequency) divided by the speed of light. Put simply, a photon of higher frequency has more momentum than one of low frequency.
When a photon hits a solar sail (or hits anything, really), it is absorbed and then re-emitted. Imagine standing on very slick ice when somebody throws a baseball to you. When you catch it (absorb the photon) you get pushed away from the person who threw it to you. When you throw it back (emit the photon), you get another equal push. That’s how reflection works, and is the key to solar sail propulsion.
The effect of a single photon is minuscule though, since the speed of light is a very big number to divide by, so it takes A LOT of them to push anything.
Thankfully, the sun puts out a mindbogglingly large number of photons. Let’s think about just how many.
The following is admittedly kind of an oddball way to calculate this, but it is more easily graspable than the more common method of using a calorimeter to measure a small patch and then multiplying it out.
To perceive a point of light the human eye needs about 7000 visible photons per second to pass through the pupil, which is about 6 square millimeters in size when dark-adapted. (Technically, it needs this many to hit the retina, but the pupil is smaller and it is the gatekeeper so the pupil is what counts when you’re talking about a point-source, which is what we’ll have here.)
Our sun is bright enough to be just barely perceptible from 55 light years away. So imagine a spherical surface 110 light years in diameter. Your pupil could anywhere on that surface and still get just enough photons to see the sun (assuming no obstructions).
The surface area of a sphere is 4πr². Let’s express it in square millimeters since that’s what we’re using for the pupil. That’s a surface area of 6.5 × 10²¹ square millimeters. The fully dark-adapted pupil is about 6 square millimeters, so divide by 6 to see how many places your pupil could be on that sphere, and we get about 10²¹ non-overlapping places. (Clearly, we’re rounding, but these are all estimates anyway.)
Since the sun is visible from all those places, that means that each of those places gets 7000 photons per second, so multiply by 7000. This tells us that the sun is pumping out 7 × 10²⁴ randomly distributed photons every second.
Seven septillion. Every second of every day. That’s obviously a rough estimate, but it’s reasonably close.
To show just how big that number is, think of it this way: If the sun were putting out one visible photon per second, it would take about six trillion times the current age of the universe for it to put out as many visible photons as it currently puts out every single second of every day. Just our sun, all by itself.
Mind blown yet? I hope not, because there’s something HUGE missing in all the above…
All that math only takes into account photons within the visual spectrum. There are a lot of photons being emitted by the sun outside the visible range as well.
As it turns out, as fun and interesting as that seven septillion visible photons per second is, the total number of photons emitted every second is actually 60,000,000,000,000,000,000 times greater!!!
Seven septillion TIMES sixty quintillion!
The actual number is approximately 4.2 × 10⁴⁴. Every second.
NOW your mind has permission to be blown.
How many of those photons hit your sail is a function of the sail’s surface area and shape, its distance from the sun, and its angle relative to the light coming from the sun.
But the point is, it’s a lot. Like, a WHOLE lot. And it’s a very good thing that the effect is so minuscule for each photon: If it was even just a little bigger for each photon, the entire solar system would be blown to smithereens.
Left- A modern lacewing larvae, bottom right- 110 million year old lacewing encased in amber, top right- artist rendering of the discovered specimen.
Lacewings are a group of insects with an interesting larval behavior; they have protrusions from their backs that they decorate with various objects they find in their environment as a form of camouflage.
They aren’t alone in this behavior; some types of crabs will also decorate themselves in order to better blend in with their surroundings. It is speculated that they may even be selective about what they choose, rather than just allowing any old thing to stick to their backsides. This is a relatively complex behavior that makes one question the intelligence required, especially in something like a larval insect.
It also causes one to wonder where along the evolutionary path this behavior first exhibited itself. Lacewing insect fossils previously found in the Dominican Republic are dated to 45 million years but a recent discovery pushes the date further still. Michael Engel a Paleontologist from the University of Kansas co-authored a paper about their discovery.
What they found was a 110 million year old larval lacewing encased in amber. The amber acting like a sepia colored time capsule preserved not only the insect but pieces of ancient fern tangled within the protrusions on its back. This pushes the date of camouflaging lacewings back 65 million years further, and according to Engel, “it’s also the earliest occurrence of this camouflaging behavior among insects as a whole.”
The fossil was discovered by a Ricardo Pérez-de La Fuente of the University of Barcelona, a doctoral student. They speculate that since the Lacewing lineage goes back to the Jurassic period, the behavior may go back as far as well.
Particle physics. Ultimately, showing someone the standard model and then expecting them to understand particle physics is a bit like someone watching a documentary on the pyramids of Giza and then being expected to decipher the cryptic hieroglyphics lining the walls on the inside. Both are things that will take years of study to fully understand (and even then, there is a lot we don’t get).
That being said, we have compiled a beginner’s guide to the basics of the Standard Model terminology, and included some very common misconceptions and descriptions of the more abstract workings. With particle physicists, they like to have all similar sounding names to describe different groups of particles, which can get very confusing. But hopefully, after reading this, you will better understand particle physics and the various articles that contain the subject matter.
First, let’s talk about hadrons. Hadrons are defined as any particle consisting of multiple quarks. In essence, they form different particles ranging from mesons (two quark particles) to baryons (three quark particles). The most common baryons are the ones found inside the nucleus of atoms, called nucleons. (These are known as the familiar proton, and the unstable neutron.) This is an area of extremely density, with a small radius that is typically 100 000 times smaller than the radius of the electrons that orbit it. As strange as that sounds, it is where the majority of the mass can be found, in the form of energy.
The important thing to note with nucleons is that they are full of stuff popping in and out of existence, for only a brief amount of time (sometimes called ‘quantum foam,’ other times, we call the phenomenon ‘virtual particles’), but overall have no net flow of energy. The conservation of quantum numbers (like electric charge), with 2 up quarks and a down quark in a proton, and 2 down quarks and an up quark in a neutron, keeps everything consistent, in midst of the crazy field fluctuations inside a nucleon.
One of the most glorious triumphs of physics over the last 100 years is the precise framework we call the Standard Model of Particle Physics. It constitutes 6 leptons and 6 quarks. The rows themselves are in arbitrary positions, but they to do go in horizontal order from smallest to largest.
There are 6 quarks. From the order of lightest to heaviest (in terms of mass-energy) they consist of the up, charm, top quarks in row 1; and the down, strange, bottom quarks in row 2. They all have fractional charge, and they are never observed on their own (fractional charges do not exist in nature). This means quarks can only to be inferred indirectly through experiments. The top 3 have the fractional charge of 2/3, the bottom three have -1/3. These are mediated, or interact amongst each other through the massless, force carrier particle called the gluon, described by the quantum field theory QCD, or quantum chromodynamics. We will get into this more in part 2 of this article.
Also note, because quarks are not massless, some theoretical physicists have postulated that they may be divided up into particles called Preons. The nature of this possibility is largely speculation at this point in time.
These particles – the Leptons – are the bottom six of the Standard Model table. These consist of the electron, muon and tau particles (in row 3). There is also the electron neutrino, muon neutrino, and the tau neutrino in row 4. The neutrinos do not have a charge, the electron, muon and tau particles all have a charge of -1. Neutrinos are peculiar in the fact they oscillate between their flavors, depending on their initial energy and the distance they travel, but not much else is known about them. They are the subject of great interest for explaining the matter/antimatter asymmetry observed in the universe. Or in other words, why there is matter existing at all, if they all are suppose to get annihilated by their antiparticles.
All of these particles (quarks and leptons) are called fermions. As you will begin to notice, physicists like to use names with the suffix ‘on’ regularly, just to make understanding particle physics seem that much harder (!). All fermions have their own antiparticle, which have the exact opposite properties as their matter counterparts, a mirror image if you will. Fermions, or particles that constitute fermions (like protons and neutrons) are subjected to the Pauli exclusion principle (PEP) and have spin property of 1/2, called half integer spin.
In short, the PEP describes how these particles cannot share the same quantum state, as defined by their intrinsic set of numbers (like angular momentum, spin, ect) . In other words, no two identical particles (thus with the same properties) can have the same exact same location in an atom, or anywhere else in the universe – for that matter. The PEP, combined with electromagnetism, is the reason why matter can have any substance at all.
This strong, sudden and sharp repulsion from the Pauli exclusion principle – fighting against a longer-ranged and smoother attraction of gravitation and electromagnetism – is what forms everything we see around us in the universe, so it’s fairly important. The PEP is also responsible for halting the gravitational collapse of white dwarfs (through electron degeneracy pressure) and neutron stars (neutron degeneracy pressure). That is, until an object gets massive enough where nothing can stop the gravitational collapse from happening, forming a black hole.
In the next article, I will talk a bit about the bosons and the forces they mediate. So stay tuned.