I read an entire book about the Tunguska explosion when I was in junior high, but it's interesting that astronomers now think an event like this could happen every 300 years.
One interesting detail I found, I think, on Wikipedia, is that if the meteor had hit about four hours later, due to Earth's rotation, it would have roughly hit Saint Petersburg.
If such events happen so frequently, we're pretty lucky so far. Given that much of Earth is covered in water, I could imagine a lot of these simply hit the ocean, but I don't know what would happen if it hit close to the coast.
a simple hit of ocean might be more devastating than hitting uninhabited parts of taiga. think about massive tsunami (at least that's what I would expect, depending on the impact force of course)
> think about massive tsunami (at least that's what I would expect, depending on the impact force of course)
You'd need something way more powerful than the Tunguska event; ignoring that Tunguska was most likely an airburst (not an impact), its estimated yield was about twice the Castle Bravo yield which did generate relatively inconsequential waves compared to the rest of its issues.
A "true" tsunami requires absolutely ridiculous amounts of water displacements, that doesn't happen with anything short of existential-risk impactors. Operation Hardtack confirmed that nuke-level energy didn't come close: there isn't enough displacement and that displacement is very temporary.
Tsunamis are generated by water displacement from e.g. underwater seismic activity or a massive landslide. Wind-driven waves or tides would be driven by sustained forces.
Whether or not an asteroid can/has cause(d) a tsunami I don't know.
A sufficiently energetic meteor strike will cause a high enough amplitude wave to qualify as tsunamis (and which therefore would produce destructive effects onshore).
Exact modelling is tricky, but that sort of thing appeals to some geophysicists.
The problem with the latter is that it will cause a nuclear winter. So that 75% will not die instantly but in 2-3 years after the impact. Add an order of magnitude or even half of that and then you have an extinction level event. It could kill organisms even at microbe level.
Keep in mind that when taking about the diameter of a three dimensional object, the amount of stuff scales with the cube. The second one is a million times more meteor.
I'm reminded of Killing Star by Charles R. Pellegrino and George Zebrowski. Even without aggressive aliens, stuff falling toward the galaxy's central black hole may get ejected at relativistic velocity. Very unlikely. But we wouldn't see it until it was almost here.
Well, we're getting photons and probably cosmic rays from Sagittarius A, so not that unlikely. :-)
You're right about small mass but macroscopic objects though, since Sag A's rotation is very sub-extremal, its mass is sufficiently high (higher mass means less curvature just outside the horizon), and its accretion structures and jets are sufficiently dim that there is essentially no chance for a rocky object to get any sort of gravity assist, much less to relativistic speeds.
Much smaller black holes are likely sources of "dangerous" gravity assists, but they also usually have accretion structures whose ICS-boosted radiation would probably disintegrate candidate objects.
On the other hand, even a fairly small chunk of rock boosted to near the speed of light would pretty much end Earth. (Time to dig up https://what-if.xkcd.com/1/ :) )
"up to 2 million miles per hour" is pretty slow compared to the speed of light :-)
These stars are in Kepler orbits so the speed tells us the relationship between their mass and the central mass. We can also use their periastrons to trace out the minimal radius of the central mass. Whatever's there is almost certainly a supermassive black hole. Gas or dust or a swarm of smaller black holes in the same radius would undergo gravitational collapse (and light up LIGO! and probably put out a lot of electomagnetic radiation too... but Sag A* is not very bright).
The UCLA Galactic Centre Group has a bunch of cool information about this sort of thing. You might enjoy:
I'm curious if we could mine in areas where large asteroids impacted and gets lots of minerals. Why do asteroid mining if we already have a few in the ground?
I saw a documentary a couple of years back which looked into a correlation of former (likely/suspected) meteor impact sites and natural resources. It looked like lots of areas rich in interesting metals/minerals turned out to probably have been hit by meteors in the past.
So in a way, we are doing that already (at least if that documentary was not totally bogus).
• Elements more volatile than metals (say, water) boil off and/or ablate off during atmospheric entry. If we want to have those, we'll need to mine them in space and shield them during re-entry.
That is assuming we even want to bring those minerals back to Earth. Most proposals intend to use them in-situ to supply spaceborne operations – theoretically, launching the equipment necessary to strip-mine an asteroid is vastly cheaper than sending up the same amount of raw resources. If we can refine those resources efficiently enough in space, things like the ISS or Lunar bases become a lot cheaper.
One factor is that we can choose which of perhaps hundreds of thousands of asteroids are worth mining, while with past impacts we only get what we happen to have been given.
I did a short analysis on the all the different types and sizes of meteorites if you are interested. The data is based on the meteorite dataset provided by the US Meteoritical Society.
> Given a long enough time period, there is a nearly 100-percent chance an asteroid large enough to destroy most life on Earth will impact our planet.
No worries. Since quantum mechanics dictates that, given enough time, anything can happen, we can also say that given a long enough time period, life will spontaneously reappear.
A more interesting question is : what kind of delay is worth worrying about?
I mean, for instance it is known that life will remain possible on Earth for about 500 million years, after which the Sun will be too bright. We don't seriously worry about it, since so many things can happen in half a billion years that it does not make much sense to try to plan or predict anything in such a timeframe.
Similarly, I personally don't worry about an impactor of 10 km diameter or so. Such an event is so rare that it's not likely to happen in several million years. To me that's still the kind of timeframe it does not make sense to worry about. I'm sure some people will disagree though.
Eventually you'll have to start worrying about very small but existential risks if you want any chance of preventing them. If the potential costs are as huge as they are with meteor impacts, I think the expected value of preparation is big enough.
The way to do this is to make it profitable to worry about it.
Some say that certain asteroids are worth trillions. While they're probably not worth quite that much, they're a pretty penny. Investors might be interested in a company designed to capture and harvest asteroids.
It will probably take a few centuries before that's a possibility, but it's interesting that it's probably just a matter of time before it doesn't sound so crazy.
The professor is lecturing, and says, "The Sun will grow to be a red giant, destroying all life on Earth in about a billion years...."
A distracted student suddenly sits up and cries out, "Oh my god!"
The professor says, "What's wrong? A billion years is a long time, you know. Nothing to worry about."
The student is visibly relief. "Oh, great! I thought you said a million years!"
Personally, I'd say a few hundred years is probably the reasonable max, maybe a thousand years. Beyond that, technology will be so incomprehensibly different that the risks and challenges will be completely different as well. What would be a civilization-killing asteroid today might just be "ooh, tasty resources already on a convenient trajectory" tomorrow. Or "aw shucks, it's going to make a big splash in the gray goo."
I strongly suspect that our species is already on its way to inevitable extinction, and much more quickly than a few hundred years.
Barring some science fiction scenarios, fertility has dropped below replacement and is of a nature where it never truly rises. Children who grow up in a low-fertility environment learn behaviors and personality traits that encourage and enhance the already-low fertility, and any who are atypical and have above-replacement fertility themselves are never enough to get the global average back to (or above) replacement. Not only have we trained the kids to have few kids themselves, we've trained them to train those few kids of their own the same (but with extra!).
You can disagree, almost everyone does. But the implications of disagreement are bizarre, you must imagine some future where all 5th generation-only children wake up and say "I want 2.1 children" or 10 percent of those 5th generation children wake up and say "I want 20 children".
Long ago I read "essai de prospective demographique"[1] written by French demographers. They were raising the concerns you mention and were trying to warn the public of a coming "demographic winter". So your point of view is not rare.
That being said, even if a demographic winter would probably have very adverse consequences, as it is not clear how well the industrialized society would fare if the population was drastically reduced, I have hard time picturing how that could lead to the complete extinction of mankind.
There will always be pockets of population with high fertility, at the very least among highly religious communities. Even if as you suggest reproductive behavior is transmitted, that works both ways, and simple natural selection will always, in the end, favor the reproductive behavior that leads to increasing numbers.
Demographic winter is a serious concern, but I can't imagine it leading to a complete extinction.
> There will always be pockets of population with high fertility,
What makes you say that? Is there some underlying principle I've failed to consider?
> I have hard time picturing how that could lead to the complete extinction of mankind.
It's simple math. Below-replacement fertility leads to extinction. More people die than are born, and since the original number is finite, the end number must be zero.
If you think that will not happen, what you're imagining is that the fertility rate will either rise at some point in the future, or at least plateau at whatever number leads to a stable population.
Why would they rise? If you grow up in a world where everyone around you has few children, then you grow up thinking/feeling that few children is the way things should be. You have few yourself. You might even have fewer than your parents' generation... but you'll rarely if ever have more. On average, you'll never have more.
Even in the fertility hot spots, this is true. They're above replacement fertility still, but each generation has a lower number. It's not exactly some sort of hidden trend, it's pretty basic.
> at the very least among highly religious communities.
It looks like the children of these communities break away from their religious upbringing at a higher rate than their pious siblings can replace with nephews and nieces. Especially in those religious communities that are unable to achieve a healthy economy... the FLDS communes that dispose of their sons, the ultraorthodox jews in their own self-imposed ghettos where there is little employment to be had.
> Even if as you suggest reproductive behavior is transmitted,
That's a little silly of me, actually. It must be the one behavior pattern that isn't transmissible.
> and simple natural selection will always, in the end, favor the reproductive behavior
The natural universe has no favorites. It does not preclude this sort of extinction. Those few who buck this trend will be starved for adequate mates at some point, and will raise their own children in a culture that ostracizes fertility...
> What makes you say that? Is there some underlying principle I've failed to consider?
Low fertility rates is a statistical rule. It's not absolute. There will always be people with high fertility, at the very least because they will be at the edge of the bell curve. Also again, look at religious communities, like the Amish. Those people do exist. Among seven billion human beings, you certainly can find a few millions that are very much willing to make babies. It only takes a small minority to ensure that the numbers will not go to zero.
> The natural universe has no favorites. It does not preclude this sort of extinction.
The lineage of people who don't have children will simply disappear, leaving room for the lineage of people who do. It's as simple as that.
> Why would they rise?
The fertility rate will rise because people with low fertility rate will die with no children. What will remain will be the children of people with high fertility rate, and presumably those children will have a similar reproductive behavior than their parents. Low fertility reproductive behavior will be "naturally" filtered out.
> Those few who buck this trend will be starved for adequate mates at some point, and will raise their own children in a culture that ostracizes fertility...
Fertility declines, but it's quite a stretch to talk about ostracization of fertility. And ostracization is not prohibition.
Low fertility doesn't lead to extinction in a few hundred years. Let's say the average is one child per woman (even places like Japan are above this), then it still takes 23 generations to reduce the global population to a thousand people, and a further ten generations to reduce to one.
Use Japan's fertility rate and you can roughly double those numbers.
I also don't see why disagreement has bizarre implications. World fertility rate is still somewhat above replacement, so all you really need is for the populations currently having lots of babies to keep on doing so. And even if the trend continues way downwards, reversal doesn't require weird scenarios where all children suddenly decide to have twice as many children as their parents. If fertility rates go from 1.5 to 2.5 over the course of ten generations, that would do it too.
Nobody really understands why fertility rates drop with wealth, so it's not weird to think that further changes could cause them to increase again, especially in a world with a much lower population than today.
> World fertility rate is still somewhat above replacement,
World fertility is only above replacement because of a few hot spots that have high fertility. As those cultures are converted to something more western-looking, fertility plummets.
You're postulating that, somehow, this will reverse and those places will convert the west to something not-so-western-looking, or that they'll fail to convert.
Both of these seem very unlikely.
Do you see any trends or evidence that either of those will come to pass?
> Low fertility doesn't lead to extinction in a few hundred years. Let's say the average is one child per woman (even places like Japan are above this), then it still takes 23 generations to reduce the global population to a thousand people, and a further ten generations to reduce to one.
It's a compounding effect. When there are only one thousand people, you still expect those who grew up in such an environment will still somehow manage a fertility rate of 1.0?
What will allow you to hit 1.0 and plateau at that for 33 generations?
> Nobody really understands why fertility rates drop with wealth,
That's easy to understand. As individuals can be mentally ill, so can large groups of people be so collectively. And collectively, the world is neurotic.
> so it's not weird to think that further changes could
"When there are only one thousand people, you still expect those who grew up in such an environment will still somehow manage a fertility rate of 1.0?"
OK, so you're going to declare that not only will fertility drop way lower than it is today, but that even in a hypothetical future where overpopulation is not a problem it must continue to drop.
And somehow my ideas are "miracles" but your ideas are obviously true.
I get the impression you're not actually open to ideas on this.
> but that even in a hypothetical future where overpopulation is not a problem it must continue to drop.
This supposes that population is currently dropping because of overpopulation. I see no evidence of that. China is your best candidate as a counterexample, and it falls flat.
They've rescinded the one child policy. If you are right, fertility should climb there... but the initial indications are that a people trained to be low-fertility continue to be low-fertility even after the training stops.
> Barring some science fiction scenarios, fertility has dropped below replacement and is of a nature where it never truly rises.
Its dropped because of shifting economic incentives. Its pretty simple to shift those incentives to shift it back the other way to some degree (and almost certain to happen if, for an extended period of time, the developed world sees negative overall growth counting both natural growth and immigration.)
> You can disagree, almost everyone does. But the implications of disagreement are bizarre, you must imagine some future where all 5th generation-only children wake up and say "I want 2.1 children" or 10 percent of those 5th generation children wake up and say "I want 20 children".
No, I just imagine a future where policymakers -- having known for generations the policy factors which promote low birth rate -- look at the situation in their countries, recognize that negative natural growth is no longer being offset by immigration, tweak the policies so that reproduction is more incentivized, resulting in the overall growth rate rising out of negative territory. Its not people magically waking up with different preferences, its people reacting to different situations with different policies and changing the payoff matrices people face in society with the same preferences.
Once in a million years is not equal to a million years later. If an asteroid hit the earth today, a million years later one could say that the probability of an asteroid hitting earth is once in a million years.
The sun getting bright is different than a meteorite impact. The latter has a Poisson distribution; a big one could hit next year, and the one following that in 10, but it also could be many thousands of years before the next big hit.
On the other hand, if our understanding of astrophysics is even remotely correct, the sun will not get too bright for the first 100,000 years. So, it makes perfect sense to not worry about the sun now, as it will not happen soon.
I also expect some governments have spent time thinking of what to do in case of impending “once in 500 million years” events (probably lumped together with all smaller ‘end of life on earth’ events. The big question here will be: (when) do you tell the public?)
Because things can only happen until entropy heat-death. Then there's not enough energy to do anything. Stuff stops happening. And that's in, what, 20 trillion years? So bounded.
{ edited: trillion }
Ha! 10^30 years by some estimates. So, a thousand billion billion billion years. Anyway, bounded.
Numbers aside, there is nothing in our universe that suggests that we shouldn't take the concept of future timelike infinity seriously, and some evidence that we should, notably the accelerating metric expansion of space.
That in turn gives us a receding horizon, which gives us Unruh radiation, which gives us fluctuations (and there are other sources for those), and that in turn poses all sorts of theoretical problems ranging from outright Poincaré recurrence to "mere" Boltzmann brains. Getting rid of these when you take infinity seriously is a theoretical challenge.
If we could prove that the universe will not expand forever, that would be a nice outcome of research in physical cosmology.
That's cute, but the statement doesn't even suggest all life would be gone. If I had to guess, "most life on Earth" would be the majority of macrofauna and macroflora.
In other words, life would probably still persist in some form (life...finds a way) and would continue evolving.
* What is the "4 billion years ago impact" that is refered in the video? At first I thought it was the Theia impact, but the sizes and speeds don't quite match, and the simulation doesn't result in a second moon.
* It also mentions that it has happened 6 times. The only impact large enough I can remember of the top of my head that sort of matches that scale would be the canadian impact basin. A quick search on wikipedia tossed me to this list [0] but everything there seems to be on a different scale than what's described in the video. Are those impacts mentioned in the full program?
* It was recently reported that an expedition drilling in a part of the ocean where the crust is thin had found microbes near the magma, but I can't find any link. Given that it has been theorized even Venus may hold life in it's upper atmosphere [1], my guess would bethat, life is far more resilient than we imagine it to be.
A fun science fiction read is "Singularity" by Bill DeSmedt; the premise is the Tunguska event being a mini-black hole - and it's caught inside the earth, eating it from the inside out.
I love that book. I listened to his podiobook version of it a few years ago. It still seems scary despite how very unlikely the scenario is to be true.
I would argue it's much better. I don't want to give away too much of the story but it has lots of questions about physics, politics, and alternate history. It's quite a good read.
> With this in mind, we can view our future with some certainty. Something big is going to smash into us, sooner or later, and probably sooner.
I started reading Cosmos by Carl Sagan a week ago and he discusses the Tunguska event for several pages. It's an amazing book that I wish I had studied long ago. Had I not read that book, this statement would have instilled an impending sense of doom into me, which does nothing but demoralize me. Now that I've read that book, I can now tell with certainty that this prophecy is utter crap. As this article mentions, the asteroids are being tracked, so, we most likely will know it before hand.
> Before you freak out, there's no chance that the asteroid is going to smash into us. The space agency is still determining its exact trajectory, but at the closest estimate, it'll be 18,000 km (11,000 miles) away as it passes us by - which would make it easily viewable with the help of a telescope. To put that into perspective, that's roughly one-twentieth the distance from Earth to the Moon. Alternatively, the asteroid could travel further afield, and pass us at a distance of around 14 million km (9 million miles).
> The reason for the big difference in these two estimates is that NASA only discovered this asteroid three years ago - hence the very-catchy name, asteroid 2013 TX68 - and haven't had much time to observe it just yet.
The Tunguska+Tesla event is quite fascinating (the whole life of Tesla is actually).
People love to make up a lot of theories and conspiracies, it's nothing new.
What is particularly worrisome is that Tesla was a very brillant man and that he believed himself to have caused this. From the information that we have, it wasn't a marketing stunt by his entourage. The guy himself was working on this particle-beam for some time and claimed to have triggered it that night. He tried to sell the technology for more almost 3 decades.
Was this made up, was this a coincidence, or did it actually happen?
Extraordinary claims require extraordinary proof. "No one is certain" is not the right way to approach the possibility that Tesla actually caused Tunguska.
And Tesla did nothing of note from that time onward. Did the suspicion that he was responsible for thousands of deaths, and that he'd invented a weapon too terrible to contemplate, cause him to retreat from his work? Hard to think otherwise.
This site[0] appears to provide a referenced timeline and breakdown of the feasibility of Tesla's particle beam weapon. The author's conclusion seems to be that, while the principle may be sound (particle beams do exist), in actual practice the energy required to meet Tesla's claims would be infeasible even in the modern era - and certainly would have been impossible in Tesla's day.
However, The "death ray" proper only appears to have been developed decades after Tunguska (Tesla mentions working on it in 1934, Tunguska was 1908[1]), so it seems to be out of the running as a possible catalyst. The Tesla Society, predictably, has a page on this[2] that links to a number of articles from the time[3] describing Tesla's claims about wireless energy transmission and its potential as a weapon.
Could Tesla's energy experiments have caused the Tunguska Event? That probably depends on the plausibility of his ideas about long-range power transmission.
Wireless tranmission of electricity is possible, however, that alone doesn't mean the idea scales. Unfortunately, because Tesla, finding an objective, scientifically grounded discussion of Tesla's ideas and technology given modern knowledge on the internet was difficult. Quora[4][5] implies that Tesla, for all his genius, simply didn't realize his process would have been too inefficient to work at the scales he envisioned. As with the "death ray," it seems the energy required would have been impossible[6].
Nikola Tesla also claimed to have created an earthquake generator - which was debunked on Mythbusters[7][8]. He also claimed to be in contact with aliens[8]. The truth about Nikola Tesla is, while he was an unparalleled genius, he was also sometimes spectacularly wrong.
I'm wondering if Tesla's equipment may have provided a standing wave to ground the ionosphere or some such technobabble. Certainly he didn't wield the power to make such a blast. But the Earth has powers that large.
And Yeah Mythbusters. They 'busted' the myth than you can start a fire using a stick and a bow. Yet my Boy Scouts do this for fun all the time.
Fair enough, although I saw them start a fire with a bow drill on an episode not too long ago. Report back when your Boy Scouts cause an earthquake with Tesla's oscillator.
There is a great twitter feed, @AsteroidMisses, that tweets out based off a NASA monitoring dataset. Browsing it provides some perspective on just how many asteroids are whizzing around the Earth all the time.
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[ 3.7 ms ] story [ 137 ms ] threadIf such events happen so frequently, we're pretty lucky so far. Given that much of Earth is covered in water, I could imagine a lot of these simply hit the ocean, but I don't know what would happen if it hit close to the coast.
You'd need something way more powerful than the Tunguska event; ignoring that Tunguska was most likely an airburst (not an impact), its estimated yield was about twice the Castle Bravo yield which did generate relatively inconsequential waves compared to the rest of its issues.
A "true" tsunami requires absolutely ridiculous amounts of water displacements, that doesn't happen with anything short of existential-risk impactors. Operation Hardtack confirmed that nuke-level energy didn't come close: there isn't enough displacement and that displacement is very temporary.
I think that if the asteroid is big enough to make a massive deadly tsunami, it will also create a very big mess if it hit the land.
Tsunamis are generated by water displacement from e.g. underwater seismic activity or a massive landslide. Wind-driven waves or tides would be driven by sustained forces.
Whether or not an asteroid can/has cause(d) a tsunami I don't know.
Exact modelling is tricky, but that sort of thing appeals to some geophysicists.
Funny headlines, serious research:
http://news.ucsc.edu/2003/05/355.html http://www.livescience.com/49298-asteroids-causing-tsunamis....
A 100 m object will flatten some trees in Siberia.
A 10 000 m object will kill 75% percent of all species on the planet (the KT event).
Lets start testing this stuff now... may also solve the greenhouse gas problem.
I'm reminded of Killing Star by Charles R. Pellegrino and George Zebrowski. Even without aggressive aliens, stuff falling toward the galaxy's central black hole may get ejected at relativistic velocity. Very unlikely. But we wouldn't see it until it was almost here.
You're right about small mass but macroscopic objects though, since Sag A's rotation is very sub-extremal, its mass is sufficiently high (higher mass means less curvature just outside the horizon), and its accretion structures and jets are sufficiently dim that there is essentially no chance for a rocky object to get any sort of gravity assist, much less to relativistic speeds.
Much smaller black holes are likely sources of "dangerous" gravity assists, but they also usually have accretion structures whose ICS-boosted radiation would probably disintegrate candidate objects.
On the other hand, even a fairly small chunk of rock boosted to near the speed of light would pretty much end Earth. (Time to dig up https://what-if.xkcd.com/1/ :) )
The impact description in Killing Star is similar to xkcd's, for what it's worth.
These stars are in Kepler orbits so the speed tells us the relationship between their mass and the central mass. We can also use their periastrons to trace out the minimal radius of the central mass. Whatever's there is almost certainly a supermassive black hole. Gas or dust or a swarm of smaller black holes in the same radius would undergo gravitational collapse (and light up LIGO! and probably put out a lot of electomagnetic radiation too... but Sag A* is not very bright).
The UCLA Galactic Centre Group has a bunch of cool information about this sort of thing. You might enjoy:
http://www.galacticcenter.astro.ucla.edu/animations.html
So in a way, we are doing that already (at least if that documentary was not totally bogus).
Two problems with this:
• There's not that many meteorites to go around.
• Elements more volatile than metals (say, water) boil off and/or ablate off during atmospheric entry. If we want to have those, we'll need to mine them in space and shield them during re-entry.
That is assuming we even want to bring those minerals back to Earth. Most proposals intend to use them in-situ to supply spaceborne operations – theoretically, launching the equipment necessary to strip-mine an asteroid is vastly cheaper than sending up the same amount of raw resources. If we can refine those resources efficiently enough in space, things like the ISS or Lunar bases become a lot cheaper.
(Practice is, as always, a lot more complicated.)
https://en.wikipedia.org/wiki/Sudbury_Basin
Site: https://jigdel.github.io/projects/meteorites/index.html
No worries. Since quantum mechanics dictates that, given enough time, anything can happen, we can also say that given a long enough time period, life will spontaneously reappear.
I mean, for instance it is known that life will remain possible on Earth for about 500 million years, after which the Sun will be too bright. We don't seriously worry about it, since so many things can happen in half a billion years that it does not make much sense to try to plan or predict anything in such a timeframe.
Similarly, I personally don't worry about an impactor of 10 km diameter or so. Such an event is so rare that it's not likely to happen in several million years. To me that's still the kind of timeframe it does not make sense to worry about. I'm sure some people will disagree though.
What is the limit? 10,000 years? 1,000? 100?
Some say that certain asteroids are worth trillions. While they're probably not worth quite that much, they're a pretty penny. Investors might be interested in a company designed to capture and harvest asteroids.
It will probably take a few centuries before that's a possibility, but it's interesting that it's probably just a matter of time before it doesn't sound so crazy.
The professor is lecturing, and says, "The Sun will grow to be a red giant, destroying all life on Earth in about a billion years...."
A distracted student suddenly sits up and cries out, "Oh my god!"
The professor says, "What's wrong? A billion years is a long time, you know. Nothing to worry about."
The student is visibly relief. "Oh, great! I thought you said a million years!"
Personally, I'd say a few hundred years is probably the reasonable max, maybe a thousand years. Beyond that, technology will be so incomprehensibly different that the risks and challenges will be completely different as well. What would be a civilization-killing asteroid today might just be "ooh, tasty resources already on a convenient trajectory" tomorrow. Or "aw shucks, it's going to make a big splash in the gray goo."
Barring some science fiction scenarios, fertility has dropped below replacement and is of a nature where it never truly rises. Children who grow up in a low-fertility environment learn behaviors and personality traits that encourage and enhance the already-low fertility, and any who are atypical and have above-replacement fertility themselves are never enough to get the global average back to (or above) replacement. Not only have we trained the kids to have few kids themselves, we've trained them to train those few kids of their own the same (but with extra!).
You can disagree, almost everyone does. But the implications of disagreement are bizarre, you must imagine some future where all 5th generation-only children wake up and say "I want 2.1 children" or 10 percent of those 5th generation children wake up and say "I want 20 children".
That being said, even if a demographic winter would probably have very adverse consequences, as it is not clear how well the industrialized society would fare if the population was drastically reduced, I have hard time picturing how that could lead to the complete extinction of mankind.
There will always be pockets of population with high fertility, at the very least among highly religious communities. Even if as you suggest reproductive behavior is transmitted, that works both ways, and simple natural selection will always, in the end, favor the reproductive behavior that leads to increasing numbers.
Demographic winter is a serious concern, but I can't imagine it leading to a complete extinction.
1. https://books.google.fr/books/about/Essai_de_prospective_d%C...
What makes you say that? Is there some underlying principle I've failed to consider?
> I have hard time picturing how that could lead to the complete extinction of mankind.
It's simple math. Below-replacement fertility leads to extinction. More people die than are born, and since the original number is finite, the end number must be zero.
If you think that will not happen, what you're imagining is that the fertility rate will either rise at some point in the future, or at least plateau at whatever number leads to a stable population.
Why would they rise? If you grow up in a world where everyone around you has few children, then you grow up thinking/feeling that few children is the way things should be. You have few yourself. You might even have fewer than your parents' generation... but you'll rarely if ever have more. On average, you'll never have more.
Even in the fertility hot spots, this is true. They're above replacement fertility still, but each generation has a lower number. It's not exactly some sort of hidden trend, it's pretty basic.
> at the very least among highly religious communities.
It looks like the children of these communities break away from their religious upbringing at a higher rate than their pious siblings can replace with nephews and nieces. Especially in those religious communities that are unable to achieve a healthy economy... the FLDS communes that dispose of their sons, the ultraorthodox jews in their own self-imposed ghettos where there is little employment to be had.
> Even if as you suggest reproductive behavior is transmitted,
That's a little silly of me, actually. It must be the one behavior pattern that isn't transmissible.
> and simple natural selection will always, in the end, favor the reproductive behavior
The natural universe has no favorites. It does not preclude this sort of extinction. Those few who buck this trend will be starved for adequate mates at some point, and will raise their own children in a culture that ostracizes fertility...
Low fertility rates is a statistical rule. It's not absolute. There will always be people with high fertility, at the very least because they will be at the edge of the bell curve. Also again, look at religious communities, like the Amish. Those people do exist. Among seven billion human beings, you certainly can find a few millions that are very much willing to make babies. It only takes a small minority to ensure that the numbers will not go to zero.
> The natural universe has no favorites. It does not preclude this sort of extinction.
The lineage of people who don't have children will simply disappear, leaving room for the lineage of people who do. It's as simple as that.
> Why would they rise?
The fertility rate will rise because people with low fertility rate will die with no children. What will remain will be the children of people with high fertility rate, and presumably those children will have a similar reproductive behavior than their parents. Low fertility reproductive behavior will be "naturally" filtered out.
> Those few who buck this trend will be starved for adequate mates at some point, and will raise their own children in a culture that ostracizes fertility...
Fertility declines, but it's quite a stretch to talk about ostracization of fertility. And ostracization is not prohibition.
Use Japan's fertility rate and you can roughly double those numbers.
I also don't see why disagreement has bizarre implications. World fertility rate is still somewhat above replacement, so all you really need is for the populations currently having lots of babies to keep on doing so. And even if the trend continues way downwards, reversal doesn't require weird scenarios where all children suddenly decide to have twice as many children as their parents. If fertility rates go from 1.5 to 2.5 over the course of ten generations, that would do it too.
Nobody really understands why fertility rates drop with wealth, so it's not weird to think that further changes could cause them to increase again, especially in a world with a much lower population than today.
World fertility is only above replacement because of a few hot spots that have high fertility. As those cultures are converted to something more western-looking, fertility plummets.
You're postulating that, somehow, this will reverse and those places will convert the west to something not-so-western-looking, or that they'll fail to convert.
Both of these seem very unlikely.
Do you see any trends or evidence that either of those will come to pass?
> Low fertility doesn't lead to extinction in a few hundred years. Let's say the average is one child per woman (even places like Japan are above this), then it still takes 23 generations to reduce the global population to a thousand people, and a further ten generations to reduce to one.
It's a compounding effect. When there are only one thousand people, you still expect those who grew up in such an environment will still somehow manage a fertility rate of 1.0?
What will allow you to hit 1.0 and plateau at that for 33 generations?
> Nobody really understands why fertility rates drop with wealth,
That's easy to understand. As individuals can be mentally ill, so can large groups of people be so collectively. And collectively, the world is neurotic.
> so it's not weird to think that further changes could
Yes, miracles will happen.
OK, so you're going to declare that not only will fertility drop way lower than it is today, but that even in a hypothetical future where overpopulation is not a problem it must continue to drop.
And somehow my ideas are "miracles" but your ideas are obviously true.
I get the impression you're not actually open to ideas on this.
This supposes that population is currently dropping because of overpopulation. I see no evidence of that. China is your best candidate as a counterexample, and it falls flat.
They've rescinded the one child policy. If you are right, fertility should climb there... but the initial indications are that a people trained to be low-fertility continue to be low-fertility even after the training stops.
I'm not exactly shocked.
Its dropped because of shifting economic incentives. Its pretty simple to shift those incentives to shift it back the other way to some degree (and almost certain to happen if, for an extended period of time, the developed world sees negative overall growth counting both natural growth and immigration.)
> You can disagree, almost everyone does. But the implications of disagreement are bizarre, you must imagine some future where all 5th generation-only children wake up and say "I want 2.1 children" or 10 percent of those 5th generation children wake up and say "I want 20 children".
No, I just imagine a future where policymakers -- having known for generations the policy factors which promote low birth rate -- look at the situation in their countries, recognize that negative natural growth is no longer being offset by immigration, tweak the policies so that reproduction is more incentivized, resulting in the overall growth rate rising out of negative territory. Its not people magically waking up with different preferences, its people reacting to different situations with different policies and changing the payoff matrices people face in society with the same preferences.
On the other hand, if our understanding of astrophysics is even remotely correct, the sun will not get too bright for the first 100,000 years. So, it makes perfect sense to not worry about the sun now, as it will not happen soon.
As to the limit: the Dutch design their sea defences for “once in a 10,000 year” events and their river defences for “once in 1,250 year” events (http://www.larouchepub.com/eiw/public/2005/2005_30-39/2005-3..., http://blog.longnow.org/02011/03/09/the-10000-year-storm/)
I also expect some governments have spent time thinking of what to do in case of impending “once in 500 million years” events (probably lumped together with all smaller ‘end of life on earth’ events. The big question here will be: (when) do you tell the public?)
A universe of infinite possibilities does not have to include a particular possibility or set of possibilities.
... but there are also built-in assumptions in that calculation. For example that certain constants will remain constant.
EDIT: Typo
That's not even close to the most conservative estimates.
https://en.wikipedia.org/wiki/Graphical_timeline_from_Big_Ba...
https://en.wikipedia.org/wiki/Timeline_of_the_far_future
That in turn gives us a receding horizon, which gives us Unruh radiation, which gives us fluctuations (and there are other sources for those), and that in turn poses all sorts of theoretical problems ranging from outright Poincaré recurrence to "mere" Boltzmann brains. Getting rid of these when you take infinity seriously is a theoretical challenge.
If we could prove that the universe will not expand forever, that would be a nice outcome of research in physical cosmology.
In other words, life would probably still persist in some form (life...finds a way) and would continue evolving.
* What is the "4 billion years ago impact" that is refered in the video? At first I thought it was the Theia impact, but the sizes and speeds don't quite match, and the simulation doesn't result in a second moon.
* It also mentions that it has happened 6 times. The only impact large enough I can remember of the top of my head that sort of matches that scale would be the canadian impact basin. A quick search on wikipedia tossed me to this list [0] but everything there seems to be on a different scale than what's described in the video. Are those impacts mentioned in the full program?
* It was recently reported that an expedition drilling in a part of the ocean where the crust is thin had found microbes near the magma, but I can't find any link. Given that it has been theorized even Venus may hold life in it's upper atmosphere [1], my guess would bethat, life is far more resilient than we imagine it to be.
[0] https://en.wikipedia.org/wiki/List_of_impact_craters_on_Eart...
[1] http://web.archive.org/web/20110807004311/http://gltrs.grc.n...
Is the DeSmedt book better?
I started reading Cosmos by Carl Sagan a week ago and he discusses the Tunguska event for several pages. It's an amazing book that I wish I had studied long ago. Had I not read that book, this statement would have instilled an impending sense of doom into me, which does nothing but demoralize me. Now that I've read that book, I can now tell with certainty that this prophecy is utter crap. As this article mentions, the asteroids are being tracked, so, we most likely will know it before hand.
OTOH, here's an article from science alert
http://www.sciencealert.com/next-month-an-asteroid-will-pass...
> Before you freak out, there's no chance that the asteroid is going to smash into us. The space agency is still determining its exact trajectory, but at the closest estimate, it'll be 18,000 km (11,000 miles) away as it passes us by - which would make it easily viewable with the help of a telescope. To put that into perspective, that's roughly one-twentieth the distance from Earth to the Moon. Alternatively, the asteroid could travel further afield, and pass us at a distance of around 14 million km (9 million miles).
> The reason for the big difference in these two estimates is that NASA only discovered this asteroid three years ago - hence the very-catchy name, asteroid 2013 TX68 - and haven't had much time to observe it just yet.
http://www.reformation.org/tesla-and-tunguska.html
People love to make up a lot of theories and conspiracies, it's nothing new.
What is particularly worrisome is that Tesla was a very brillant man and that he believed himself to have caused this. From the information that we have, it wasn't a marketing stunt by his entourage. The guy himself was working on this particle-beam for some time and claimed to have triggered it that night. He tried to sell the technology for more almost 3 decades.
Was this made up, was this a coincidence, or did it actually happen?
It's been over 100 years and no one is certain.
edit: clarified what "this" means
Apparently there's still no scientific consensus (is that even possible?) on the Tunguska explosion and NASA seems to acknowledges that.
Taken from: http://science.nasa.gov/science-news/science-at-nasa/2008/30...
"A century later some still debate the cause and come up with different scenarios that could have caused the explosion," said Yeomans"
No remains of the asteroid, no impact crater and the claims from Tesla together is what is fascinating to me.
However, The "death ray" proper only appears to have been developed decades after Tunguska (Tesla mentions working on it in 1934, Tunguska was 1908[1]), so it seems to be out of the running as a possible catalyst. The Tesla Society, predictably, has a page on this[2] that links to a number of articles from the time[3] describing Tesla's claims about wireless energy transmission and its potential as a weapon.
Could Tesla's energy experiments have caused the Tunguska Event? That probably depends on the plausibility of his ideas about long-range power transmission.
Wireless tranmission of electricity is possible, however, that alone doesn't mean the idea scales. Unfortunately, because Tesla, finding an objective, scientifically grounded discussion of Tesla's ideas and technology given modern knowledge on the internet was difficult. Quora[4][5] implies that Tesla, for all his genius, simply didn't realize his process would have been too inefficient to work at the scales he envisioned. As with the "death ray," it seems the energy required would have been impossible[6].
Nikola Tesla also claimed to have created an earthquake generator - which was debunked on Mythbusters[7][8]. He also claimed to be in contact with aliens[8]. The truth about Nikola Tesla is, while he was an unparalleled genius, he was also sometimes spectacularly wrong.
[0]http://www.danielcelton.com/2015/01/13/is-teslas-particle-be...
[1]https://en.wikipedia.org/wiki/Tunguska_event
[2]http://www.teslasociety.com/tunguska.htm
[3]http://www.tfcbooks.com/articles/tunguska.htm
[4]https://www.quora.com/Why-hasnt-anyone-attempted-to-rebuild-...
[5]https://www.quora.com/Does-this-project-to-rebuild-Teslas-Wa...
[6]https://skeptics.stackexchange.com/questions/14869/is-there-...
[7]https://en.wikipedia.org/wiki/Tesla's_oscillator
[8]https://www.discovery.com/tv-shows/mythbusters/about-this-sh...
[9]http://www.bibliotecapleyades.net/tesla/esp_tesla_11.htm
And Yeah Mythbusters. They 'busted' the myth than you can start a fire using a stick and a bow. Yet my Boy Scouts do this for fun all the time.
Tesla's whole idea since the beginning was to harness the earth energy itself to produce and power his invention.
Now, did he really find a way to do this more than 100 years ago?
I love to dream that there's that much energy just lying beneath our feet and all around us waiting to be used.
https://twitter.com/asteroidmisses