Gamma-Ray SETI

Gamma-ray bursts are cosmic phenomena. As far as terrestrial astronomers go, they are unexpected (you can’t point your telescope in advance knowing where and when one will happen) and they are short-lived (so when one is detected you have a rather limited window of opportunity to point your telescope). Now, the question arises, are they all totally natural phenomena, or could some be manufactured, and like artificially generated radio waves, perhaps contain a message in a cosmic bottle? - A message of interest to those who seek out new life and new civilizations.

SETI (Search for ExtraTerrestrial Intelligence) scientists search for ET’s intelligent messages in the radio spectrum; and also in the visible region of the electromagnetic spectrum. Should they, despite the inherent difficulties, take the opportunity to analyse gamma-ray bursts for a signal in the gamma radiation noise? If they in fact they already have been examined for a signal I’m unaware of it or any such analysis and conclusions. It’s those unexpected and short-lived aspects that make gamma-ray SETI difficult in the extreme. It’s like sometime in the next 24 hours, on just one radio station, in some unspecified part of the world, lasting for only ten seconds, you will hear a voice. Good luck picking it up.

Gamma-ray bursts were discovered accidentally by the Vela series of satellites. The Vela satellites were sent up by the Americans to keep tabs on those naughty commies and to make sure they didn’t violate the Nuclear Test Ban Treaty. The Vela satellites indeed picked up one of the telltale signatures of atmospheric nuclear explosions (gamma-rays), except they weren’t coming from Terra Firma or within our atmosphere, but somewhere out there – way, way, way out there. Though first detected in 1967, the anomalous nitty-gritty details weren’t made public until about six years later – well these after all were top secret military spy-in-the-sky satellites.

Anyway, it was quickly realized that these cosmic gamma-ray bursts were coming from really, really far away. They weren’t sourced locally; they weren’t sourced at interplanetary distances, or even at interstellar distances. They were happening in galaxies far, far away, so far, far away that they happened a long, long time ago too (since it takes electromagnetic radiation, of which gamma-rays are a part thereof, finite times to cross finite distances). To cross such vast distances with such energy intensities suggested that gamma-ray bursts were not akin to a galaxy what a firecracker is to Planet Earth. Rather, it was more a galactic case of, well a terrestrial super-duper nuclear explosion on Planet Earth. 

Now gamma-rays are very high energy electromagnetic photons, more energetic than ultraviolet and X-rays. Even before the detection of those intergalactic gamma-ray bursts, we knew about gamma-rays since they are a natural product of electron – positron annihilation and of some radioactive decay processes.

So much for some background on gamma-rays and astronomical bursts of gamma radiation, how might that apply to SETI? Let’s assume that there is at least one highly advanced technological extraterrestrial civilization somewhere out there, who wishes to draw attention to themselves via a signal of some sort (which is not quite the same thing as actual one-on-one communication).  That desire might be akin to a more relevant terrestrial analogy like an anomous show-off graffiti artist – “here I am; I exist”. How would, or at least could, our ET do it?

Now what’s the biggest cosmic bang advertisement for your buck you can get? My understanding would be matter-antimatter annihilation. If an electron meets a positron, you get a gamma-ray. So, I wonder whether the rather anomalous and unpredictable gamma-ray bursts that are somewhat common, but not too common in the cosmos, might, or at least some of them might, be artificially created by that highly technological extraterrestrial civilization or perhaps, if plural, those extraterrestrial civilizations. An alien ‘message’ (as it were) or signal, in plain sight.

Here’s another possible scenario. Say once upon a time, billions of years ago, you had various, even numerous, high-tech extraterrestrial civilizations in various galaxies. In the classification scale of ET civilizations they would fall somewhere between a Type II (mastery of the energy output of a stellar object) and a Type III civilization (mastery over the energy resources of an entire galaxy). They shared information (‘communication’ in real time being out of the question due to the intergalactic distances involved) via radio waves, laser beams, etc. It’s efficient to send an electromagnetic packet of info in a tightly compressed, and short-lived, burst. In-person travel to and on-site visitations, possible in interplanetary and interstellar scenarios, are impossible when it comes to intergalactic scenarios. The distances are just too vast.

Now, Cosmology 101, the expanding universe, tells us that most galaxies are moving away from most other galaxies. To keep intergalactic ‘communications’ or data sharing viable over the long term, you need to shout louder as time goes by; as your neighbouring or nearby galaxies gets farther and farther away from you. Gamma-ray bursts are ‘louder’ than most other energetic phenomena in the Universe. The basic data sending principle is the same. If you can use light waves or radio waves, etc. to send a message, why not a gamma-ray?

The drawback is that this is really high-energy expenditure. But, if you are a Type II or Type III civilization, ‘burning’ this amount of energy is akin to a billionaire lighting a match.

Now the odds are very high that in all probability, gamma-ray bursts are a totally natural phenomenon, albeit still a very mysterious one. But, you never know. I think it premature to rule out ET, at least until such time as we have a better grounding in the theory behind them and/or do a detailed analysis of a typical gamma-ray burst happening looking for some signal in the cosmic noise but not finding any.

The Mythology of the Night Sky: Part Two

We’re all quasi familiar with the stars in the night sky; some more than others which often depends on whether you’re in the centre of a brightly lit polluted city sky or out in the clear dark air of rural – wherever. To the ancients, those bright lights in the night sky weren’t just bright lights in the night sky, but actual representations of their myths and legends. Time and time again their gods rewarded various characters with immortality, not by turning them into deities, but by placing them forever and a night in the heavens for all to see and remember.

One of the highest honours any demigod, demigoddess, mortal male or female, or beast for that matter could be awarded in Greco-Roman times would be to immortalized as a star or a constellation in the heavens. Here’s a few of those that achieved that honour.

Continued from yesterday’s blog…

*Eosphoros [see] Venus.

*Eridanus [see] Auriga, the Charioteer.

*Equuleus, the Pony: In Greek mythology, Pegasus, the winged horse, had either a brother or son, the foal Celeris (meaning "swiftness" or "speed"). Celeris was given to Castor (one of the two Gemini twins) by Hermes (Mercury to the Romans). Another version has Equuleus as the horse struck from Poseidon’s trident during a pissing contest between him and the goddess Athena when contesting who would be the superior patron of Athens (that name gives away who won). Because Equuleus’s section of stars rises before the constellation of Pegasus, it is often called Equus Primus, or the First Horse. See also Pegasus.

*Ganymede [see] Aquarius, the Water-Carrier.

*Gemini, the Twins: The Dioscuri, the “Sons of Zeus” or the “Heavenly Twins” are better known as Castor and Polydeuces (who is even better known as Pollux). Despite the “Sons of Zeus” tag, Pollux was the son of Zeus and Leda, and Castor the son of Leda and her husband, the King of Sparta. However they were twins, and brothers to Helen (of Troy), daughter of Zeus and Leda. When Castor was fatally wounded, Pollux asked Zeus to let him die alongside his beloved brother. They were eventually placed among the stars as the constellation we know as Gemini.

*Hercules was finally undone by an act of deception. His wife without knowing the true facts of the matter had Hercules put on a poisoned robe, which was akin to him bathing in a tub of acid. In agony, the demigod builds his own funeral pyre and lays on it awaiting death. A passing King of Malis, a former Argonaut, Poias, lights the pyre. An almighty thunderclap booms out as the pyre started burning as Zeus took Hercules up to Olympus and made him an immortal god. Even his stepmother, Hera, finally give up her intense anger towards him and they were reconciled. To honour his son, Zeus set up the stars in the constellation now named for him. See also Draco, Hydra and Leo.  

*Hesperus [see] Venus.

*Hyades (star cluster) [see] Pleiades.

*Hyas [see] Pleiades.

*Hydra, the Snake (or Water-Snake): After Hercules killed the Hydra (his second of twelve labours), the Hydra was placed in the firmament by Athena as the constellation Hydra, the Snake (or Water-Snake). See also Corvus, the Crow and Hercules.

*Ladon [see] Draco, the Dragon.

*Leo, the Lion: The first great labour of Hercules was to slay the great Nemean Lion who was invulnerable to arrows and spears and swords, etc. So, Hercules had to choke the beast to death. Hercules wore the skin of the lion as a cloak, and Zeus, to honour his son’s completion of his first Mission: Impossible task was to place the lion in the sky as a memorial – the constellation Leo. See also Hercules.

*Lyra: Orpheus, son of one of the nine Muses, was a highly skilled musician and singer who could charm the gods, mortals and beasts alike. However, when Orpheus eventually came to a sticky end, Zeus immortalized his music by placing his lyre among the stars as the constellation Lyra. Orpheus himself went to and stayed put in Hades, but that’s actually a happy ending, for he was forever reunited with his wife Eurydice, who he earlier, when alive, tried to rescue from the underworld, but failed to do so.

*Orpheus [see] Lyra.

*Ophiuchus, the Serpent Bearer: Asclepius, the son of Apollo and a mortal woman, turned out to be an extremely skilled physician. So skilled was he than he actually brought a corpse back to life! This was frowned on by Zeus as it got into deity only abilities, so Zeus smote him with his thunderbolts (and the now alive corpse as well). Now this pisses off Apollo, so in turn he smites the Cyclopes, the makers of those lethal thunderbolts. Now this as you would expect pisses off Zeus, so he forces Apollo into servitude to a mortal for one year as punishment. Meantime, as Asclepius was depicted with a staff with a snake coiled around it, he was immortalised as the eternal symbol in the heavens, the constellation Ophiuchus, the Serpent Holder (or Bearer). See also Sagitta.

*Orion: Orion, the mighty hunter, lusted after the Pleiades (the seven sisters) and their mum, so Zeus put the lot of them in the heavens thus out of Orion’s and harms way. Orion finally met his doom by boasting once too often about hunting and killing the wildlife, and so his was stung to death by a giant scorpion by orders of the earth goddess Gaia. On behalf of several of the gods or goddesses (Artemis and Leto) Zeus placed Orion too in the heavens, behind and forever chasing after those Pleiades sisters. The scorpion, for services rendered was also places in the heavens as the constellation Scorpio, still in pursuit of Orion! As an almighty hunter, Orion was accompanied by a hunting dog, the constellation Canis Major which includes the brilliant Dog Star, Sirius. 

*Pegasus: Pegasus, the winged horse was the offspring of the god of the sea, Poseidon (often identified with all things equine) and the gorgon Medusa, born when Perseus sliced off Medusa’s head. Pegasus was caught and tamed by Bellerophon, the two of which made a good team when Belleraphon slew the Chimera from the air and out of harms way.  But, he became unstuck when he tried to use his aerial transport and fly Pegasus to Olympus uninvited. Zeus, furious at the presumption that Bellerophon could just waltz into the abode of the gods any old time, sent an insect to sting Pegasus, causing the winged horse to throw off its rider, Bellerophon, who, without benefit of a parachute eventually went splat. Though Bellerophon survived the crash, he was crippled for life. Zeus then utilized Pegasus to draw his chariot filled with his thunderbolts, and as a final reward, placed Pegasus among the stars. See also Equuleus, the Pony.

*Perseus, who killed the gorgon Medusa, also rescued the lovely Andromeda from a sea monster, Cetus. Perseus and Andromeda of course married and had a son, Perses, but Parses was entrusted to and raised by King Cepheus (father of Andromeda) who needed a male heir to his throne (in Ethiopia). Now King Cepheus was married to the vain Cassiopeia (mother of Andromeda) who bragged she was better looking than the sea nymphs, the Nereids. The Nereids complained to their boss, Poseidon, the god of the sea who spat the dummy and demanded that her child, Andromeda of course, be sacrificed to Cetus, the sea monster, as retribution. That’s when Perseus happened by. All five, after they died their natural deaths, were placed among the stars as the constellations named after them. But Cassiopeia was placed upside down in the heavens to teach her some humility.

*Phaethon [see] Auriga, the Charioteer.

*Phosphorus [see] Venus.

*Pleiades (star cluster): The Pleiades, seven sisters all, were born of the Titan god Atlas and the Oceanid, Pleione. Prior to that Titan mated via the Oceanid Aithra producing a son, Hyas and his sisters, the Hyades. Thus the Pleiades were half-sisters to Hyas and the Hyades. Now one day Hyas was out hunting and was killed in the process by his prey, probably a boar. His sisters, the Hyades, died in turn from grief suffered by the loss of their beloved brother. In a triple-hankie story, their half-sisters, the Pleiades, also died, one and all, out of grief. Zeus, out of sympathy, immortalised the lot of them. Hyas and the Hyades as the star cluster Hyades; close in the sky to that of the Pleiades star cluster. The alternative version is that the hunter Orion had the hots for the seven sisters so Zeus intervened and transferred them to the sky where Orion couldn’t bother them. Of course later on, Orion too gets placed among the stars in the sky and to this day endlessly chases after the Pleiades. See also Orion.

*Pollux [see] Gemini.

*Sagitta, the Arrow: In ancient Greece, Sagitta was regarded as the weapon that Hercules used to kill the eagle (Aquila), an eagle that Zeus employed that perpetually gnawed at Prometheus’s liver. That was punishment for Prometheus’s ‘gift of fire’ to mankind, in defiance of Zeus’s instructions to the contrary. Another version believes the Arrow to be the one shot by Hercules towards the Stymphalian birds, his sixth labour. Those winged creatures had claws, beaks and wings of iron, and they lived on human flesh. Hercules got rid of the lot of them. Yet another version claimed it as the arrow with which Apollo exterminated the original trio of Cyclopes because the Cyclopes forged the thunderbolts for Zeus which Zeus used to kill Apollo’s son, Asclepius. See also Ophiuchus.

*Sagittarius: While undertaking his fourth labour, Hercules accidentally hit the centaur Chiron with one of his arrows that had been tipped with poison from the Hydra he killed earlier. Because the centaur was immortal and couldn’t die, he was doomed to be forever in agony. Zeus relieved him of his immortality, allowing Chiron to pass away, but Zeus in one manner restored Chiron’s immortality when he placed the centaur in the sky as the constellation Sagittarius. See also Centaurus.

*Scorpio [see] Orion.

*Sirius [see] Orion.

*Taurus, the Bull: When the king of the gods, Zeus, had his wicked way with Europa, he did so by shape-shifting into the form of a bull and carried Europa across the sea to Crete in that form, where they ‘did it’ (presumably Zeus shape-shifted back to human form before they ‘did it’). Since that time Crete (known as the Minoan culture or civilization) has had a long association with bulls or a bull-cult, like the sport of bull-jumping (grabbing the horns and somersaulting onto the back of the animal) and hosting half-a-bull as in the Minotaur. Because the bull-form suited Zeus so well, he immortalized the animal as the constellation Taurus.

*Ursa Major, the Great Bear: Callisto was the daughter of the King of Arcady, and she had the misfortune to have Zeus fall for her. Callisto was associated with the virgin goddess Artemis. When Zeus raped Callisto, she got in a family way (in mythology, every rape results in a pregnancy otherwise there’s no point to the rape in the first place). This rape ultimately produces a son, Arcas. Artemis, being the virgin, was livid and banished Callisto from any further association with her. Hera (Mrs. Zeus) in the meantime assumed Callisto was a willing partner to her wayward hubby and in revenge turned Callisto into a bear. Years later, Arcas, out hunting, ran across that bear and not realizing that it was mom, shot her dead. Zeus then placed Callisto into the zodiac as Ursa Major, the Great Bear (or the Big Dipper); Arcas ultimately got his place in the heavens too as the Little Bear (or the Little Dipper).

*Ursa Minor [see] Ursa Major

*Venus: Eos (Dawn) or to the Romans Aurora, born to Astraios all of the stars in the sky, of which two were most notable: Phosphorus (or Eosphorus), the Morning Star, and Hesperus, the Evening Star. In reality, both ‘stars’ are one and the same ‘star’ and not stars at all but the planet Venus.  

*Virgo [see] Bootes.

It’s a pity all that came to an end. If you were living way back then, perhaps you too might have been immortalised as a star, a star cluster or perhaps even as a constellation to be recorded for posterity, seen and talked about by millions for generations upon generations to come.

Can Black Holes Evaporate? Part Two

While there is a constant transfer of matter and radiant electromagnetic energy (photons) between bodies throughout the cosmos, there are sinks, ultimate final resting places where matter/energy can retire to and be removed from the rest of the cosmos. These cosmic sinks are Black Holes. But is that retirement permanent, or can stuff re-enter the cosmic workforce? Can Black Holes evaporate? The theoretical short answer is “yes”; the long answer is “no”.

Continued from yesterday’s blog…

Now what about a Black Hole? Clearly a Black Hole isn’t isolated from the rest of the cosmos and objects therein. If you were just outside the event horizon you’d ‘see’ photons (of all wavelengths) because you’d see stars and galaxies, etc. just like you can locally. Neutrinos would still pass right through you on their way to their doom once passing through the event horizon. The Universe is full of interstellar and intergalactic atoms and molecules and dust and of course lots of larger stuff a Black Hole can snack on. Black Holes will sweep up stuff just like Earth does, only more so since it has more gravity with which to grab hold of stuff with, and also because once caught there’s no escape for the cosmic fish. Unlike Earth, everything that crosses that event horizon, that hits the Black Hole, won’t be reflected back (like photons). Neutrinos that can pass through light-years worth of solid lead without even ‘breathing hard’ will be imprisoned when they try that trick in a Black Hole’s inner sanctum. And of course atoms, molecules, interstellar dust, the big chunks will also get imprisoned. 

But we can imagine an idealized cosmos where all Black Holes have swallowed up all existing radiated particles (photons), all the atoms,  molecules, the dust and all the bigger stuff – all those stars and planets; asteroids and comets; even all that mysterious ‘dark matter’. So you have a cosmos of just Black Holes and the vacuum energy (well maybe a few bits and pieces escaped, but so few to be of no consequence).  Of course there is one further logical extension. Black Holes can swallow other Black Holes. Black Holes can merge to form bigger Black Holes. The final product is that the cosmos consists of one Black Hole – the Mother of all Black Holes – plus the vacuum energy!  So you end up with one Black Hole left standing with nothing left to eat.

Okay, so the only scenario now possible is that this Mother of all Black Holes evaporates via Hawking radiation. It might take trillions upon trillions upon trillions of years, but evaporate it does. Since matter and energy can neither be created nor destroyed, once the Mother of Black Holes has finally gone ‘poof’, the Universe is right back where it started from – full of stuff from photons to fundamental particles which them undergo chemistry to form atoms and molecules and stars and planets and perhaps life – and new Black Holes!

Perhaps this is a new and improved version of a cyclic/oscillating universe! - But then again, maybe not. There’s a fly in that ointment (but I had you going for a while back there!). That “idealized cosmos” was only a ‘what if’ thought experiment.

Firstly, it’s actually very, very unlikely all the Black Holes in the Universe will ever merge together as long as the Universe keeps expanding. Since the galaxies are getting farther and farther away from each other due to that expansion, the collection of Black Holes contained within each galaxy keep getting further and further apart from other clusters of Black Holes contained within other galaxies. It’s like the passengers in one car get more and more remote from the passengers in another car when each car is going at different velocities and heading in different directions.

Now the collection of all Black Holes in any one galaxy could well coalesce into one super Black Hole galaxy. You have a galaxy that instead of containing billions and billions of stars and debris and particles now consists of just one Black Hole – the car only has one occupant. You have a pure Black Hole galaxy, or a galactic sized Black Hole. 

One might end up with a Universe composed of just these pure Black Hole galaxies, all spreading farther and farther apart over time. 

But secondly, there’s another fly in the ointment. All the space that separates these pure Black Hole galaxies from each other isn’t a perfect vacuum, quite apart from the vacuum energy. All the radiating stars and stuff may have been gobbled up within each galaxy, but all of interplanetary space, all of interstellar space, and all of intergalactic space, isn’t pure vacuum. There’s still the ‘it’s everywhere, it’s everywhere’ Cosmic Microwave Background Radiation (CMBR).

So what’s this CMBR?  If you have a massive hot explosion (like the Big Bang event is alleged to have been), and all that heat energy expands and expands, then you’d expect the temperature of the area occupied by that energy to drop, the temperature ever decreasing as the volume that finite amount of energy occupies increases. As the energy expands it gets diluted and thus cools, but can never reach an absolute zero temperature for reasons already noted. And that’s just what we find on a universal scale. There’s a fine microwave energy “hiss” representing a temperature a few degrees above absolute zero that’s absolutely everywhere in the cosmos. That’s the diluted heat energy of the very hot Big Bang – well it has been a long time since the Big Bang event (13.7 billion years worth of time) and that energy is now spread throughout a lot of cosmic volume. That microwave “hiss”, called the CMBR, was predicted way before it was discovered. There’s no doubt that it exists.

Since the CMBR is just photons with very long wavelengths, Black Holes could suck up the CMBR photons as easily as light photons. Removal of CMRB photons, already representing a temperature just slightly about the theoretical minimum – absolute zero – would mean the Universe gets even colder, which it would anyway since the Universe is ever expanding and thus available electromagnetic energy (photons) is ever diluting. Combining the two effects and the Universe is a chilly place indeed and will get even colder.

However, it’s probably not possible for Black Holes collectively to swallow up all of the CMBR since there will come a point of diminishing returns. What happens when the temperature of Black Holes equals the temperature of the Universe at large – the CMBR? The answer is thermal equilibrium like when your hot cup of coffee cools off to room temperature. Input into Black Holes from the CMBR will equal output via Hawking radiation. For every photon emitted via Hawking radiation, a CMBR photon gets sucked in. What does that mean? It means a Black Hole can not evaporate.

What about very tiny (micro) Black Holes that are relatively ‘hot’? Might they go ‘poof’ before thermal equilibrium is achieved? Will the contents of the Black Hole evaporate into the surrounding cosmos before they can equate to the surrounding temperature? The analogy might be like a hot drop of water could evaporate into the cold atmosphere before the liquid water drop can attain the temperature of its surrounding environment.

Even so, I still imagine that in the current matter and radiation dominated Universe, incoming would still exceed outgoing.

Of course if you could take a Black Hole, isolate and shield it from the rest of the cosmos and all that it contains, so all you have is the Black Hole and its internal energy (including the all pervading vacuum energy therein). An isolated Black Hole would be in a setting equivalent to putting it into an absolute zero temperature environment. If that’s the case then outgoing would exceed incoming since there could be no incoming, and therefore that Black Hole would then radiate and slowly evaporate and eventually go ‘poof’. BUT, and there’s always a BUT, I can not envision any scenario where a Black Hole can exist in such a theoretical isolation. So, Professor Hawking is quite correct – in theory. In practice, in the here and now, input exceeds Hawking radiation output, and even in the unimaginably far distant future equilibrium will be established where input equals output. 

Can Black Holes Evaporate? Part One

While there is a constant transfer of matter and radiant electromagnetic energy (photons) between bodies throughout the cosmos, there are sinks, ultimate final resting places where matter/energy can retire to and be removed from the rest of the cosmos. These cosmic sinks are Black Holes. But is that retirement permanent, or can stuff re-enter the cosmic workforce? Can Black Holes evaporate? The theoretical short answer is “yes”; the long answer is “no”.

Black Holes are astrophysical objects that are so massive, that have gravity so high, that their escape velocity (some seven miles per second on Earth) exceeds the ultimate cosmic speed limit – the speed of light (186,000 miles per second). Since nothing can travel faster than the speed of light, nothing (matter and/or energy) once inside a Black Hole can ever get out again – or so the seemingly ironclad logic went.

However, that’s all according to classical physics. A physicist by the name of Jacob Bekenstein came up with the idea of applying quantum physics to Black Holes (upon a suggestion by his mentor John Wheeler – who incidentally coined the phrase “Black Hole”), and once that was done, well lo and behold, Black Holes apparently exhibited entropy, and therefore had a temperature and therefore must radiate and therefore can vomit out stuff. His ideas were mulled over and over again and finally agreed to and expanded on by the celebrated astrophysicist/cosmologist Stephen Hawking. That stuff that a Black Hole can regurgitate now goes under the name of Hawking radiation, or to give credit where credit is due it is technically Bekenstein-Hawking radiation. However, it’s usually just called Hawking radiation so I’ll stick with that convention.

Of course if Black Holes have a temperature, then they must follow the same laws of thermodynamics as any other object with temperature. One key point in thermodynamics is that energy exchanges between objects are at least partly determined by one object’s temperature compared to another object’s temperature. The temperature of a hot cup of coffee will stay hot longer the higher the temperature of the environment that surrounds that hot cup of coffee. A Black Hole’s temperature must be compared to whatever temperature surrounds the Black Hole when considering the fate of the Black Hole. So how does a Black Hole get temperature?

In retrospect, how this happens is obvious (as are all great ideas when applying hindsight).

There is no such thing as the perfect vacuum. That could only be achieved at a temperature of absolute zero where and when everything is 100% frozen stiff. Alas, such a state violates one of the most fundamental principles of quantum physics – the Heisenberg Uncertainty Principle – where it is impossible to know both the momentum and position of anything with 100% precision. If something were at absolute zero, frozen stiff and standing still, you’d know both the momentum (which would be zero) and position (at a standstill) of that something with absolute precision.

Since there is always a minimum state of energy anywhere in the Universe (something above absolute zero), and since energy and mass are equivalent (Einstein’s famous formula/equation), then that energy state, the false not-quite-absolute-zero vacuum, the vacuum energy*, can generate mass – virtual particles. However, the particles come in matter-antimatter pairs, which usually immediately annihilate and return to their former pure energy state. BUT, and there is always, a BUT – there’s an exception to the rule – that normal state of affairs can be thwarted.

The vacuum energy, that which can generate particle-antiparticle pairs, exists everywhere where existence has any meaning. Part of that existence is an area called the event horizon**, which is a concept related to the concept we call Black Holes. All Black Holes have an event horizon which surrounds them.

The event horizon surrounding a Black Hole is that somewhat fuzzy region that separates the region (below the event horizon) from which gravity rules over the speed of light, and that region (above the event horizon) where gravity’s escape velocity can’t quite dominate that speed of light velocity. I say its “fuzzy” since it’s not razor sharp, albeit nearly so.

The vacuum energy is part and parcel of the space surrounding the event horizon, above, below and spot-on. Now, what if that vacuum energy generates a pair of virtual particles, one each popping into existence above the event horizon; one below the event horizon. Then, the particles will be unable to annihilate and recombine into pure energy. One will stay within the Black Hole. The other, being above the event horizon, can be dealt a ‘get out of jail’ card. And thus, slowly, ever so slowly, but ever so surely, the Black Hole loses mass, thus energy, and evaporates.

Here’s the general picture. Black Holes can only radiate from the event horizon region which, in a very large Black Hole is going to be very cold because it’s not radiating very much, so initially only things like the mass-less photon escapes. Assuming there’s no incoming to replace the loss, the Black Hole shrinks, and as it gets smaller it warms up slightly (that’s what things that shrink tend to do) and can radiate particles with small mass – say neutrinos. When the Black Hole is tiny, it’s very warm, in a relative sense, and it can go out with a ‘bang’, maybe emitting an electron or positron which is way more massive. When there’s no more Black Hole, the vacuum energy still produces at random virtual particle pairs, but there’s no more event horizon from which to separate those virtual particle pairs and thus its all back to normal – the two annihilate and return to their vacuum energy state. That’s where the popular accounts end. End of story. The ultimate fate of Black Holes will be to evaporate via Hawking radiation, even if it does take trillions of years.

Alas, the written texts forget to mention that radiation emission (and other forms of emitted stuff) is a two-way street, not a one-way street. Black Holes can acquire stuff, as well as radiate stuff. If deposits exceed withdrawals, then Black Holes will always have a positive ‘stuff’ balance and thus won’t fully evaporate. Now this is perhaps why Hawking radiation hasn’t been observed. The tiny amount of Hawking radiation (outgoing) will be swamped by the greater, many orders of magnitude greater, amounts of incoming radiation and other stuff impacting the Black Hole.

Forget Black Holes (and their massive gravity) for a moment and concentrate on Planet Earth. Even at night, you see lots of suns – stars. You see them because they are radiating photons – particles of electromagnetic energy of which visible light is a small part. In fact you only detect a tiny fraction of visual photons because your visual detection devices (eyes) aren’t that efficient. Optical telescopes pick up a lot more of them, but they’re still just as real. You are also being hit by photons in the infrared, the ultraviolet, in radio wavelengths, X-ray photons, gamma-ray photons, etc. Though Earth’s atmosphere shields us from some of these photons (ultraviolet photons are far greater in number at the top of our atmosphere than at the bottom), you still get impacted by multi-billions of them; Planet Earth many orders of magnitude more. Some of the photons get reflected back into space; these don’t add to Earth’s energy/mass balance. Overall, there are roughly one billion photons for each and every fundamental particle with mass, like electrons and neutrinos.

Now in addition Earth (and you too) gets hit with cosmic rays, neutrinos, and cosmic dust. Even if you luck out, Planet Earth gets impacted by meteors and other outer space debris, sometimes debris large enough to not only hit the surface but do considerable damage. Planet Earth’s mass increases by many tons a day, all due to Earth’s sweeping up of the interplanetary dust and small rocks that intersect Earth’s orbit. The trillions of neutrinos that hit us are so ghostly that nearly all pass right through you and the entire planet as well despite them having a tiny amount of mass, so as far as our planet is concerned, they are of little significance. 

To be continued…

*If it helps to conceive of the concept of the vacuum energy, here’s an analogy. Think of the invisible but energetic atmosphere as the vacuum energy. Part of that atmosphere consists of invisible water vapour. But, all of a sudden, and for reasons that must have been mysterious to the ancients, part of the atmosphere undergoes a phase change into something you can see; into something solid – like a particle. You get mist/fog (clouds), rain drops, snow, sleet, hail, etc. Then, equally mysterious, those solid bits eventually undergo another phase change (evaporation standing in for annihilation) back to invisible water vapour in the equally invisible atmosphere. And so you have the invisible vacuum energy that generates particle-antiparticle pairs which annihilate back into the vacuum energy.

**The surface area of the event horizon is the same for both incoming and outgoing so there is no need to take that (non) variable under consideration.