Five questions added to my Q&A page this week, bringing the total to a nice round 50.
1) What happens to galaxies after their central black holes evaporate ?
Nothing, because all their stars will be dead and black holes just aren't that big anyway.
2) If space and time are expanding, how can we estimate the age of the Universe ?
Carefully.
3) How do we know the distances to the stars ?
By drawing big triangles IIIIIINNNNN SPPPPAAAAAACE !
4) Will our Solar System suffer from a space tidal wave ?
Nope.
5) What's the difference between gravitational waves and tidal forces ?
Waves move. Tidal forces are lazier.
The exiled life of an astrophysicist
Sunday, 26 April 2015
Saturday, 25 April 2015
The Most Astounding Fact
Neil de Grasse Tyson describes the most astounding fact as being that the elements in your body were created in the white heat of long-dead giant stars.
It's a pretty neat thing, no doubt about it. But before you get all misty-eyed or swoon from sheer misplaced romanticism, it's worth stating this in another way.
Even so, it's a great quotable fact. What could I possibly offer to trump this ? Simple.
The sky is dark at night.
If astronomy is the oldest profession (hint : it isn't), then this is surely the oldest observation. It's also, perhaps, one of the most profound. Its consequences are - quite literally - infinitely more significant than knowing where our atoms come from.
Olber's Paradox is breathtakingly simple. If the Universe is infinite in size, eternal, and full of stars, then every line of sight should end with a star. The night sky would be as bright as the surface of the Sun.
It would be quite wrong of me to omit this astonishingly good video by MinutePhysics which explains (almost) all the relevant issues in less than 4 minutes. The only downside is that it is, perhaps, a bit of a blitzkrieg of information on some pretty complicated issues.
Let's take a more sedate look at possible solutions to the paradox.
1) The stars are very far away. Duuuh !
This does seem like a good solution at first, because obviously the further away a star is, the dimmer it appears. Right ? Wrong. Well, sort-of wrong. It's true we receive less of the star's energy output, because obviously most of its light never reaches us but just carries on out into the void, so it appears dimmer. That's just simple geometry.
But there's another quantity which is more relevant here : surface brightness, or the brightness per unit area. That, it turns out, does not vary with distance at all.
Imagine that you have two large, equally powerful floodlights. One is 10m away and the other is 1000m away. Obviously, the 10m floodlight will be painful to stare at while the the 1000m floodlight won't cause you any problems. But suppose that you hide behind a wooden fence in which there is a very small hole - small enough that you can only see a small part of even the distant floodlight through it. If you look at both lights through the hole, you won't be able to tell which is which. Bizarre, but true*.
* A simplified truth, actually. I'll get back to that later.
Or, to put it another way, the stars we see only appear dim because they also look small. If you made them so large that they would appear as large as the Sun does, they'd also appear as bright as the Sun.
So unfortunately we can't use sheer distance to resolve Olber's Paradox. Booo.
2) There's something in the way.
The Universe is full of gas and dust, and those aren't bright at visible wavelengths. The problem is that given enough time, all of this gas and dust should heat up and become just as hot as the surface of a star. At which point they will also look as bright as the surface of a star. I say "a star" rather than "the Sun" because of course not all stars have the same brightness - but they all, to our eyes, have a high surface brightness. Anyway the same thing applies to dim stars as it does to dust - they'll get heated up by the infinite number of other bright stars.
One might wonder about black holes, which do not let light escape. If there was a black hole along every line of sight, would it not prevent us from seeing all of the starlight ? Well, perhaps. But this is going to mean having all the black holes set up just right so as to prevent us from seeing stars beyond a certain distance. And the mass infalling into the holes is going to have to be absolutely perfectly balanced to counter their shrinking due to Hawking radiation - otherwise they'll either grow to infinite size and consume everything, or vanish. Which is preposterous given how varied the Universe is on small scales.
3) We're looking at the wrong wavelength.
I myself have made great efforts to point out that the dark night sky we see...
... is only because visible light is not the whole story. If we could see hydrogen gas, it'd look a whole lot different.
But this is missing the point. Although there's a lot of hydrogen gas in the way, it doesn't obscure our view of the stars, so we should see with our eyes a bright sky.
A much more sophisticated argument is that maybe light changes wavelength over great distances, eventually becoming something we can't see. This "tired light" is a discredited alternative idea to explain why distant galaxies look redder. Conventional contemporary astronomy says this is because the Universe is expanding; tired light has it that light loses energy as it travels. Just where that energy is supposed to go I'm not sure.
People sometimes try to use the Cosmic Microwave Background to explain the parodox. The CMB is microwave radiation in the... cosmos... and it's in the background... well we'll get back to that. The point is that this radiation occurs across the whole sky and it's not coming from gas in our own galaxy. When analysed in detail however, whatever it is it simply cannot be from redshifted stars. So that doesn't help us explain the paradox after all.
4) Stars don't last forever.
True. We see them exploding all the time. But we also know that new stars are born as well. So if the Universe is infinite, that should still mean that there are an infinite number of stars along every line of sight.
5) Stars don't go on forever.
In one sense this is true : our Galaxy has an edge. But of course, beyond that there are more galaxies, full of stars. So far, there's no evidence that there's any sort of "edge" to galaxies. And if there were, everything should have collapsed into a big ugly heap - the Universe would have a centre which everything would slowly fall towards.
Besides, infinite space which just has a few galaxies in it is no way of resolving the paradox - it's simply a way of saying that the assumption of infinite stars is wrong.
6) The Universe is a fractal.
Oooh, this one's interesting ! Remarkably, it turns out that it is possible to have an infinite number of stars in an infinite Universe but not have every line of sight end on a star. One really obvious way to do this would be to have all the stars in a really long line. Infinite stars but lots and lots of dark sky !
Which is of course very silly because that's just not what we see. Or maybe it is. Maybe all the galaxies we see are part of an infinitely long cylinder...naah. That's just stupid*. For one thing the cylinder would collapse radially down to a line, for another, you'd only have dark sky in certain directions. But more complicated fractals can also allow for dark sky in a more interesting pattern.
* Sometimes, just sometimes, this is a legitimate argument.
This is Fournier's fractal, proposed in 1907 as one possible resolution to the paradox. Clearly it allows large parts of the sky to be dark. It can also be rendered in 3D :
You may wonder if that means that along some lines of sight there'd still be infinite stars and so infinite energy. Tricky. The idea here is that the energy density decreases as you go to larger and larger scales, so the total energy when you sum over infinity is still finite. That's actually a perfectly sensible everyday bit of mathematics for describing continuous functions, but doesn't work for discrete objects like stars. If you have a finite amount of energy, you must have a finite number of stars. Which means there's an edge to the stars, and we get back to the collapsing-heap problem again.
In any case, that's definitely not what the Universe looks like. But the concept is there. I was hoping to be able to find out more about fractals that actually do resemble the Universe, but while there's a great deal of alternative (mostly outright bonkers) ideas about the Universe being a fractal on the internet, I couldn't find a single one addressing this point. Well, I did come across one article modelling a fractal distribution of stars (not the large-scale galaxy filaments), but annoyingly I can't find it again. If anyone can provide simple instructions, I'd love to visualise this - though it's not obvious to me if such a structure is even possible (i.e. stable).
Another problem I suspect with the fractal idea is : why would the Universe remain a fractal ? Galaxies move around quite a lot. Occasionally, stars get ripped out of galaxies. Over infinite time, the nice fractal structure is going to get destroyed, and those blank areas will be filled in.
Finally, observations have demonstrated that the Universe just isn't a fractal, so this can't be the solution either.
7) The Universe isn't infinite.
We've sort of already covered this one with the idea that there aren't infinite stars. But having a finite number of stars in an infinite void of empty space is philosophically unsatisfying, as well as just plain not working. So, maybe the Universe has always existed but has a limited volume ? The nice thing about this is that space wouldn't need to have any kind of edge - curved space would allow you to travel in any direction and eventually get back to where you started.
The problem is that this doesn't avoid the everything-collapsing-to-big-ugly-heap problem. Einstein's equations show that a static Universe is unstable unless you very carefully tweak things - it's not a natural solution at all.
Now, if you'll remember the very first point, I mentioned that saying surface brightness doesn't vary with distance is a simplified truth. It works in a static Universe. It's not true in an expanding Universe - if space is expanding, surface brightness should vary in a very particular way which we can actually test, and from the results it really does seem that the Universe is expanding (there are also other reasons to believe that redshift indicates expansion and not some other effect like tired light; the cosmic microwave background is also very well explained by this).
There's also a slightly simpler argument to believe that the Universe is expanding. As I mentioned, distant galaxies look redder and this is thought to be because space is expanding, giving them the appearance of moving away from us. Of course, it could instead simply mean that every galaxy is terrified of ours and is trying like hell to get as far away from us as possible.
That only works if you think our Galaxy is somehow an incredibly special place, which most of us don't. There are good reasons for this - the Universe looks pretty similar in every direction, so it would be extremely surprising if the speed measurements didn't match this. So instead we postulate that it if we were in any other galaxy, we would still see all the other galaxies rushing away, which avoids the weirdness of us having a special position. Remarkably, this seems to work. It really is the case that the Universe is expanding. Even more amazingly, it may even be possible - one day - to measure this expansion directly in real time : to watch a galaxy's velocity change over time as the Universe expands.
And of course, if the Universe is expanding but also finite, then it cannot also be eternal.
8) Energy and mass conservation is for hippy losers !
It's true that the collapse-to-a-heap problem of a finite Universe or finite number of stars can be solved, if you provide some force to keep the galaxies moving outward (or to keep the Universe expanding). The trouble is that you could solve pretty much anything by allowing energy to be created - it would be basically saying "because magic". You'd have to have some incredibly good reason why this only happens to keep the Universe balanced, otherwise you may as well throw the laws of thermodynamics out of the window, shout "ALACKAZAM !" and watch them plummet to a firey doom.
All that said, however, the accelerating expansion of the Universe can be explained without violating the conservation of energy. So maybe something similar could stop the Universe collapsing and keep it nicely balanced - if things were set up perfectly. There would be literally zero margin for error, since over infinite time a non-static Universe would either expand to infinity (in which case we wouldn't see any other stars at all) or collapse to a point (in which case we wouldn't see anything at all).
Worse, a Universe in a truly steady state - with star birth and death precisely balanced so the Universe always appears much as it does now - requires violation of conservation of energy.
9) The Universe isn't eternal.
First, let's recap.
You could, I suppose, argue that maybe the Universe is infinite and eternal but simply doesn't always look the way it does now. After all, we know galaxies looked different in the past to how they do today - not to mention that quasars are only found in the distant (early) Universe - so clearly things have changed :
A totally steady state is out. But maybe there's a quasi-steady state of multiple Big Bangs - as the Universe expands and all the stars disperse and die, new material is suddenly created. Well, maybe. The question to ask is whether you prefer the Universe to be infinite and eternal or finite and mortal.
A mortal Universe (finite in time) solves Olber's Paradox at a stroke - or rather, it's more like cutting the Gordian Knot since it effectively declares the paradox invalid. If there hasn't been infinite time, and the Universe has been changing, there's no reason to expect a bright night sky. There was once a time when there weren't any stars, and since then stars have formed so far away that there hasn't been time for their light to reach us yet.
Strictly speaking, a mortal universe doesn't preclude it from being infinite in space. Personally I'd rather it was finite in space as well. I see infinities as problems to be avoided, not solutions to be invoked. They're a useful mathematical trick - but they also let you get away with murder. In an infinite Universe, you can explain any anomaly as being a statistical fluke, no matter how unlikely something is, it will happen somewhere. Which means there's no way of knowing if your observations are telling you something about the underlying physics at work, or if you're just in a really weird part of the Universe. And, of course, this.
Conclusion
Olber's Paradox implicitly assumes that an infinite eternal Universe is preferable. Why, I'm not sure. I suppose it might be nice to think that the Universe will go on and on forever, but personally I prefer the exact opposite. As for whether a Universe that once didn't exist will eventually cease to exist, I've no idea.
Interestingly, those people who are still convinced the Universe must be eternal (google "steady state" and "fractal cosmology") tend to do so because they see Big Bang cosmology as too religious. Seriously. Even the great Fred Hoyle (and he was great, no matter how wrong he was), one of the original proponents of Steady State theory, thought that the idea of a creation was irrational. There are many others on the internet stating things more directly : that the Big Bang is pseudoscientific idea that justifies Christianity.
I wonder what six-day Creationists have to say about that.
Of course, this is not a sensible reason to reject the theory. Things do get created and destroyed all the time, albeit from things which already exist. Most scientists accept the idea of creation from absolute nothingness without believing in a deity as the cause of it. And while religious texts are indeed full of gibberish, the idea that things got created is no more nonsensical than the idea that humans exist - which religious texts also state, but no-one is trying to debunk that.
Debunking the Big Bang because you think it's too religious is a "nuke the whales" policy - it might be fun (those cetacean jerks would do the same to us if they could), but it isn't sensible.
But whether you believe the Universe is eternal or mortal, finite or infinite (and I'm glad there are people still examining all the options, even if I do think most of them are loony), consider this. The lifetime of stars, the expansion of space, fractal geometry, the very nature of reality itself - all of these are important in understanding why the sky is dark at night. And that's why for me, it's tough to think of a more astounding fact.
Though why he feels the need to talk like William Shatner
I have no idea.
It's a pretty neat thing, no doubt about it. But before you get all misty-eyed or swoon from sheer misplaced romanticism, it's worth stating this in another way.
 |
| Yeah I've used this before, but whatcha gonna do ? |
The sky is dark at night.
If astronomy is the oldest profession (hint : it isn't), then this is surely the oldest observation. It's also, perhaps, one of the most profound. Its consequences are - quite literally - infinitely more significant than knowing where our atoms come from.
Olber's Paradox is breathtakingly simple. If the Universe is infinite in size, eternal, and full of stars, then every line of sight should end with a star. The night sky would be as bright as the surface of the Sun.
 |
| From wikipedia. |
Let's take a more sedate look at possible solutions to the paradox.
1) The stars are very far away. Duuuh !
This does seem like a good solution at first, because obviously the further away a star is, the dimmer it appears. Right ? Wrong. Well, sort-of wrong. It's true we receive less of the star's energy output, because obviously most of its light never reaches us but just carries on out into the void, so it appears dimmer. That's just simple geometry.
 |
| A planet near a star receives a greater fraction of the star's energy than one further away. The energy from the star is spread out over larger areas at larger distances. |
But there's another quantity which is more relevant here : surface brightness, or the brightness per unit area. That, it turns out, does not vary with distance at all.
Imagine that you have two large, equally powerful floodlights. One is 10m away and the other is 1000m away. Obviously, the 10m floodlight will be painful to stare at while the the 1000m floodlight won't cause you any problems. But suppose that you hide behind a wooden fence in which there is a very small hole - small enough that you can only see a small part of even the distant floodlight through it. If you look at both lights through the hole, you won't be able to tell which is which. Bizarre, but true*.
* A simplified truth, actually. I'll get back to that later.
Or, to put it another way, the stars we see only appear dim because they also look small. If you made them so large that they would appear as large as the Sun does, they'd also appear as bright as the Sun.
So unfortunately we can't use sheer distance to resolve Olber's Paradox. Booo.
2) There's something in the way.
The Universe is full of gas and dust, and those aren't bright at visible wavelengths. The problem is that given enough time, all of this gas and dust should heat up and become just as hot as the surface of a star. At which point they will also look as bright as the surface of a star. I say "a star" rather than "the Sun" because of course not all stars have the same brightness - but they all, to our eyes, have a high surface brightness. Anyway the same thing applies to dim stars as it does to dust - they'll get heated up by the infinite number of other bright stars.
 |
| Dark clouds like this one obscure stars in our Universe, but this doesn't work if the Universe is infinite and eternal. Everything should have reached the same temperature. |
3) We're looking at the wrong wavelength.
I myself have made great efforts to point out that the dark night sky we see...
But this is missing the point. Although there's a lot of hydrogen gas in the way, it doesn't obscure our view of the stars, so we should see with our eyes a bright sky.
A much more sophisticated argument is that maybe light changes wavelength over great distances, eventually becoming something we can't see. This "tired light" is a discredited alternative idea to explain why distant galaxies look redder. Conventional contemporary astronomy says this is because the Universe is expanding; tired light has it that light loses energy as it travels. Just where that energy is supposed to go I'm not sure.
People sometimes try to use the Cosmic Microwave Background to explain the parodox. The CMB is microwave radiation in the... cosmos... and it's in the background... well we'll get back to that. The point is that this radiation occurs across the whole sky and it's not coming from gas in our own galaxy. When analysed in detail however, whatever it is it simply cannot be from redshifted stars. So that doesn't help us explain the paradox after all.
 |
| You can actually see part of the CMB yourself if you don't tune in your TV correctly - a few percent of the static comes from this. At least it did back in the era of analogue telly. Not sure about this new digital era. |
4) Stars don't last forever.
True. We see them exploding all the time. But we also know that new stars are born as well. So if the Universe is infinite, that should still mean that there are an infinite number of stars along every line of sight.
 |
| The Crab Nebula, formed by a supernova explosion that was actually observed and recorded in 1054 A.D. |
5) Stars don't go on forever.
In one sense this is true : our Galaxy has an edge. But of course, beyond that there are more galaxies, full of stars. So far, there's no evidence that there's any sort of "edge" to galaxies. And if there were, everything should have collapsed into a big ugly heap - the Universe would have a centre which everything would slowly fall towards.
 |
| Welsh cosmology is the best cosmology. |
6) The Universe is a fractal.
Oooh, this one's interesting ! Remarkably, it turns out that it is possible to have an infinite number of stars in an infinite Universe but not have every line of sight end on a star. One really obvious way to do this would be to have all the stars in a really long line. Infinite stars but lots and lots of dark sky !
 |
| Worst. Universe. Ever. |
* Sometimes, just sometimes, this is a legitimate argument.
 |
| Man I hate fractals. They make my head hurt. |
You may wonder if that means that along some lines of sight there'd still be infinite stars and so infinite energy. Tricky. The idea here is that the energy density decreases as you go to larger and larger scales, so the total energy when you sum over infinity is still finite. That's actually a perfectly sensible everyday bit of mathematics for describing continuous functions, but doesn't work for discrete objects like stars. If you have a finite amount of energy, you must have a finite number of stars. Which means there's an edge to the stars, and we get back to the collapsing-heap problem again.
In any case, that's definitely not what the Universe looks like. But the concept is there. I was hoping to be able to find out more about fractals that actually do resemble the Universe, but while there's a great deal of alternative (mostly outright bonkers) ideas about the Universe being a fractal on the internet, I couldn't find a single one addressing this point. Well, I did come across one article modelling a fractal distribution of stars (not the large-scale galaxy filaments), but annoyingly I can't find it again. If anyone can provide simple instructions, I'd love to visualise this - though it's not obvious to me if such a structure is even possible (i.e. stable).
Another problem I suspect with the fractal idea is : why would the Universe remain a fractal ? Galaxies move around quite a lot. Occasionally, stars get ripped out of galaxies. Over infinite time, the nice fractal structure is going to get destroyed, and those blank areas will be filled in.
 |
| The Universe is a dynamic place. It's tough to see how galaxy motions are compatible with a fractal structure - what stops distant galaxies from moving into the regions we see as dark ? |
7) The Universe isn't infinite.
We've sort of already covered this one with the idea that there aren't infinite stars. But having a finite number of stars in an infinite void of empty space is philosophically unsatisfying, as well as just plain not working. So, maybe the Universe has always existed but has a limited volume ? The nice thing about this is that space wouldn't need to have any kind of edge - curved space would allow you to travel in any direction and eventually get back to where you started.
 |
| Specially modified version of the Virgo Cluster. |
Now, if you'll remember the very first point, I mentioned that saying surface brightness doesn't vary with distance is a simplified truth. It works in a static Universe. It's not true in an expanding Universe - if space is expanding, surface brightness should vary in a very particular way which we can actually test, and from the results it really does seem that the Universe is expanding (there are also other reasons to believe that redshift indicates expansion and not some other effect like tired light; the cosmic microwave background is also very well explained by this).
There's also a slightly simpler argument to believe that the Universe is expanding. As I mentioned, distant galaxies look redder and this is thought to be because space is expanding, giving them the appearance of moving away from us. Of course, it could instead simply mean that every galaxy is terrified of ours and is trying like hell to get as far away from us as possible.
 |
| Worst. South Park. Ever. This is why I'm not a cartoonist. |
And of course, if the Universe is expanding but also finite, then it cannot also be eternal.
8) Energy and mass conservation is for hippy losers !
It's true that the collapse-to-a-heap problem of a finite Universe or finite number of stars can be solved, if you provide some force to keep the galaxies moving outward (or to keep the Universe expanding). The trouble is that you could solve pretty much anything by allowing energy to be created - it would be basically saying "because magic". You'd have to have some incredibly good reason why this only happens to keep the Universe balanced, otherwise you may as well throw the laws of thermodynamics out of the window, shout "ALACKAZAM !" and watch them plummet to a firey doom.
All that said, however, the accelerating expansion of the Universe can be explained without violating the conservation of energy. So maybe something similar could stop the Universe collapsing and keep it nicely balanced - if things were set up perfectly. There would be literally zero margin for error, since over infinite time a non-static Universe would either expand to infinity (in which case we wouldn't see any other stars at all) or collapse to a point (in which case we wouldn't see anything at all).
Worse, a Universe in a truly steady state - with star birth and death precisely balanced so the Universe always appears much as it does now - requires violation of conservation of energy.
9) The Universe isn't eternal.
First, let's recap.
- The paradox can't be resolved by the sheer distances to the stars because brightness doesn't work like that.
- There can't be a barrier blocking our view because it would heat up to the same temperature as the stars.
- The sky is bright everywhere at other wavelengths, but the details show that this cannot possibly be due to starlight.
- The finite lifetime of stars doesn't work because stars are also born.
- If the stars only span a finite part of an infinite Universe, they would have all collapsed.
- A fractal Universe might not remain a fractal, and observations show that the Universe isn't a fractal.
- A finite Universe doesn't work because the evidence that the Universe is expanding is very strong, and therefore the Universe cannot also be eternal.
You could, I suppose, argue that maybe the Universe is infinite and eternal but simply doesn't always look the way it does now. After all, we know galaxies looked different in the past to how they do today - not to mention that quasars are only found in the distant (early) Universe - so clearly things have changed :
_Hubble.jpg) |
| The "spiderweb" galaxy seen by Hubble, about 10 billion light years away - a chaotic series of galaxy mergers. |
.jpg) |
| The Andromeda galaxy M31, just two million light years away - a stable, rotating disc. |
A totally steady state is out. But maybe there's a quasi-steady state of multiple Big Bangs - as the Universe expands and all the stars disperse and die, new material is suddenly created. Well, maybe. The question to ask is whether you prefer the Universe to be infinite and eternal or finite and mortal.
A mortal Universe (finite in time) solves Olber's Paradox at a stroke - or rather, it's more like cutting the Gordian Knot since it effectively declares the paradox invalid. If there hasn't been infinite time, and the Universe has been changing, there's no reason to expect a bright night sky. There was once a time when there weren't any stars, and since then stars have formed so far away that there hasn't been time for their light to reach us yet.
Strictly speaking, a mortal universe doesn't preclude it from being infinite in space. Personally I'd rather it was finite in space as well. I see infinities as problems to be avoided, not solutions to be invoked. They're a useful mathematical trick - but they also let you get away with murder. In an infinite Universe, you can explain any anomaly as being a statistical fluke, no matter how unlikely something is, it will happen somewhere. Which means there's no way of knowing if your observations are telling you something about the underlying physics at work, or if you're just in a really weird part of the Universe. And, of course, this.
Conclusion
Olber's Paradox implicitly assumes that an infinite eternal Universe is preferable. Why, I'm not sure. I suppose it might be nice to think that the Universe will go on and on forever, but personally I prefer the exact opposite. As for whether a Universe that once didn't exist will eventually cease to exist, I've no idea.
Interestingly, those people who are still convinced the Universe must be eternal (google "steady state" and "fractal cosmology") tend to do so because they see Big Bang cosmology as too religious. Seriously. Even the great Fred Hoyle (and he was great, no matter how wrong he was), one of the original proponents of Steady State theory, thought that the idea of a creation was irrational. There are many others on the internet stating things more directly : that the Big Bang is pseudoscientific idea that justifies Christianity.
I wonder what six-day Creationists have to say about that.
Of course, this is not a sensible reason to reject the theory. Things do get created and destroyed all the time, albeit from things which already exist. Most scientists accept the idea of creation from absolute nothingness without believing in a deity as the cause of it. And while religious texts are indeed full of gibberish, the idea that things got created is no more nonsensical than the idea that humans exist - which religious texts also state, but no-one is trying to debunk that.
Debunking the Big Bang because you think it's too religious is a "nuke the whales" policy - it might be fun (those cetacean jerks would do the same to us if they could), but it isn't sensible.
 |
| You nuke those whales, Fred. You nuke 'em good. |
Sunday, 19 April 2015
Ask An Astronomer Anything At All About Astronomy (II)
This update to my Q&A page is a week later than planned due to a (happily resolved) medical emergency.
Please remember that the purpose of a Q&A is primarily for people who want to learn about a subject. If you've got an agenda to push (i.e. an alternative theory to propose), I'm more than happy to debate it (usually) but you might want to consider that this is not necessarily the best venue for that. Though there's often an overlap, teaching is not the same as debate.
Probably the best solution is to try splitting your question into smaller, more manageable questions which individually don't lead to a conclusion. That will also reduce any bias on my part if I don't like what you're suggesting !
If in any doubt, do ask. I don't want to stifle debate, but I'd like to keep this page primarily as a place for answers. Which are admittedly a rare thing in science...
Also, this page is about astronomy. Occasionally this can overlap with other subjects such as geology and even archaeology. You can ask about them if you like, but, as St Augustine said : "It is a disgraceful and dangerous thing for an infidel to hear a Christian [theologian] talking nonsense on these [scientific] topics." In other words, non-experts should avoid embarrassing themselves by not discussing things they don't understand*. So I reserve the right to only attempt to answer questions which I think I can answer. Occasionally, that will stray beyond the boundaries of astronomy, but I'll try to minimize that as much as possible.
* I'm calling this the St Augustine defence, and it's a helpful reminder that even canonised 4th century Roman theologians didn't think the Bible should be taken literally.
The latest questions added :
1) What is time ?
Annoying.
2) How can we estimate the age of the Universe given that gravity distorts time ?
Carefully.
3) Was there a giant tsunami caused by an impact in the Indian Ocean a few thousand years ago ?
No.
4) When can we expect FTL to become a reality ?
Tomorrow. Last Tuesday (it would allow time travel). Or possibly never.
5) Can a supernova destroy a planet, and if so, how far away would it have to be ?
Anything within its own system is in, like, really serious trouble. Other star systems might be sterilised, but at least their planets won't crack open.
6) Can debris from supernovae destroy planets in other star systems ?
Yes, but it doesn't.
7) Could the asteroid belt have formed by the (recent) destruction of a planet between Mars and Jupiter, with most of its mass being thrown out of the Solar System ?
Nope.
8) Are there more moons of the outer planets than the inner planets because asteroids were flung out of the solar system by the break-up of a planet in the asteroid belt ?
Nope.
If there are any geologists / planetary geologists reading, I'd be grateful if they could check my answers to questions 3 and 8 in case I've said something very silly.
Please remember that the purpose of a Q&A is primarily for people who want to learn about a subject. If you've got an agenda to push (i.e. an alternative theory to propose), I'm more than happy to debate it (usually) but you might want to consider that this is not necessarily the best venue for that. Though there's often an overlap, teaching is not the same as debate.
Probably the best solution is to try splitting your question into smaller, more manageable questions which individually don't lead to a conclusion. That will also reduce any bias on my part if I don't like what you're suggesting !
If in any doubt, do ask. I don't want to stifle debate, but I'd like to keep this page primarily as a place for answers. Which are admittedly a rare thing in science...
Also, this page is about astronomy. Occasionally this can overlap with other subjects such as geology and even archaeology. You can ask about them if you like, but, as St Augustine said : "It is a disgraceful and dangerous thing for an infidel to hear a Christian [theologian] talking nonsense on these [scientific] topics." In other words, non-experts should avoid embarrassing themselves by not discussing things they don't understand*. So I reserve the right to only attempt to answer questions which I think I can answer. Occasionally, that will stray beyond the boundaries of astronomy, but I'll try to minimize that as much as possible.
* I'm calling this the St Augustine defence, and it's a helpful reminder that even canonised 4th century Roman theologians didn't think the Bible should be taken literally.
The latest questions added :
1) What is time ?
Annoying.
2) How can we estimate the age of the Universe given that gravity distorts time ?
Carefully.
3) Was there a giant tsunami caused by an impact in the Indian Ocean a few thousand years ago ?
No.
4) When can we expect FTL to become a reality ?
Tomorrow. Last Tuesday (it would allow time travel). Or possibly never.
5) Can a supernova destroy a planet, and if so, how far away would it have to be ?
Anything within its own system is in, like, really serious trouble. Other star systems might be sterilised, but at least their planets won't crack open.
6) Can debris from supernovae destroy planets in other star systems ?
Yes, but it doesn't.
7) Could the asteroid belt have formed by the (recent) destruction of a planet between Mars and Jupiter, with most of its mass being thrown out of the Solar System ?
Nope.
8) Are there more moons of the outer planets than the inner planets because asteroids were flung out of the solar system by the break-up of a planet in the asteroid belt ?
Nope.
If there are any geologists / planetary geologists reading, I'd be grateful if they could check my answers to questions 3 and 8 in case I've said something very silly.
Monday, 13 April 2015
200
TWWWWWOOOOO HUUUUUNNNDDDREEEEEDD POOOOOOOSSSSSSTS !
Yay !
If ever there was an excuse for the blog equivalent of a clip show, this is it. I've gone from being a bored student in Cardiff with nothing better to do that write short pointless blog posts, to a bored postdoc in Arecibo with nothing better to do than write moderate-length blog posts, and now a bored postdoc in Prague with nothing better to do than write really long blog posts. There are worse fates. Here are the highlights.
Top Five Most Viewed Posts
5 : The Curse of the SS
A simple tale about getting a social security number and the problems of having a name without any vowels in it. Apparently mentioning the old woman from Monsters Inc generated 2,500 hits. The internet is a strange place.
4 : Learning To Love The Bomb
Nuclear warheads and big shock absorbers
Towering black monoliths and contradictory orders
A deranged computer that's learning to sing
These are a few of my favourite things...
2,900 hits for the blog post, 4,300 for the video (which does not feature the song). An Orion-version of the Discovery originally considered for 2001 : A Space Odyssey but didn't make the grade.
3 : And Yet It Moves (but not like that)
Debunking some myths of a popular space video and some myths that sprang up around that video. No, our Solar System isn't a vortex, but the Solar System does move and the planets do trace helical paths some of the time. No, the video doesn't show the Sun leading the planets. 3,200 hits... but please see this more recent article. The creator of the video and I have come to an entirely amicable understanding.
2 : Infographic : Galaxy Size Comparison Chart
People love novelty, and I happened to notice that typing in "galaxy size comparison" into Google images found pictures of smartphones. It still does, but at least now the top results are my charts (7,300 hits for the original post), which have nothing to do with Samsung. Much better*. See also the equally interesting dwarf galaxy version, which is also popular with 2,100 hits.
* But if Samsung would like to buy me out, I'm listening.
1 : VY Canis Majoris : Or, Be Afraid. Be Very Afraid.
People also love comparing the sizes of things. And why not. In this case, rather than directly comparing the size of a particularly massive star with other massive stars, I decided to see what it might look like if it replaced our Sun. This got on reddit and consequently resulted in 21,000 hits to date. Which is nice because sometimes I think that the more effort I put into making things, the fewer people appreciate the result.
Top Five Most Liked Posts
5 : Happy Birthday Arecibo !
With a mere 350 hits but 119 + 1's (a.k.a. "likes") this is one of the most highly rated posts. I suspect this is because Google+ includes likes for the posted image (in this case an animated gif) as well as the post itself. Still, it's a nice, short, image-heavy post which is worth a read. The video was used at Arecibo's 50th Anniversary symposium.
4 : Galaxies Suck, Let's Get Rid Of Them
One of those, "hmm, I thought this might attract attention" posts. I can't really complain with 810 hits and 126 likes... but come on, it's an exploding galaxy ! Using a science-class simulation generously provided by a friend who owed me a favour, I examine what would happen if dark matter disappeared. Of course, this wouldn't be true if our theory of gravity is wrong, but it's a graphic way to illustrate why dark matter is so important in contemporary mainstream cosmology.
3 : Blue Marbles
In contrast to the last one, this one was a case of, "oh look, 50,000 hits, how strange". Actually it was the sequel Rocky Marbles that attracted the attention, which got reshared by I Fucking Love Science, the Daily Mail, and innumerable others. And in fact virtually all of the hits were on YouTube, with only 3,000 on the combined blog posts. 133 likes though.
2 : Project Orion : How To Nuke A Spaceship Without Killing Anyone
To my knowledge I hold the honour of creating the first ever animation of an Orion-drive spacecraft. I probably should have jumped on the YouTube bandwagon much sooner, but back in 2005 creating animations of any length on a home PC was a major undertaking so it didn't seem worth it. This one probably took > 6 months from start to finish. Of course, the animation quality in the Space Odyssey version is much better, and the realism of the detonation sequence is much higher, but this one is much closer to the original design spec. 3,500 hits (>140,000 for the video) and 171 likes.
I have frequent delusions that I should remake this in high definition, which is a fine idea if only I could find the time.
1 : Damn That's A Nice Piece Of Gas
Although viewed by a mere 1,000 people, I'm rather pleased that my most liked (189) post is all about the ultra-specialist subject of visualising neutral hydrogen data. And why not ? Neutral hydrogen is ludicrously beautiful. You should like it, or you have no soul, damnit. This view of the hydrogen in the Milky Way at different frequencies is also my most liked (>500) gif.
Top Five Most Interesting Posts That Didn't Quite Make Either Of The Above Lists Through No Fault Of Their Own, Because, Like, Seriously, They're Quite Good And You Should Read Them
5 : Quack Quack
I'm fed up with people declaring their Google skills to be superior to the years of training it takes to do real science. I'm particularly annoyed by people who declare things like, "we should stop searching for dark matter, it's an arrogant and dogmatic belief". Obviously, their arrogant and dogmatic belief that it doesn't exist trumps all the expert opinion that it probably does but might not so we should go and check to make sure. That said, some burden of the blame does lie with the scientists, and I believe we must stop stating opinions as facts - but more importantly the media has to convey science as a process, ugly and full of mistakes, not a stochastic series of amazing breakthroughs.
I'm also particular pleased with my essays on feminism and especially atheism, but any fool can be qualified to rant about them. Quack Quack, however, is an effort by a scientist to help explain the scientific method, so I can at least claim some small level of expertise on that.
4 : The Best Space Rock Ever
Asteroid 1998 QE2 is an extraordinary place. A few kilometres across, if you fell over it would take you a minute and a half to hit the ground. You could easily jump into orbit around it or even off it entirely - and if you were very careful you could say, "that's no space station, it's a moon" shortly before you landed on its tiny moon (which is barely larger than the ISS). It's also of a size where comparing it to the QE2 is a vaguely-sensible way to get an idea of how large it is. Oh, and it would float.
3 : Why Star Trek Is Clearly Better Than Battlestar Galactica
Battlestar Galactica was a depressing show, unless you realise that the entire thing was a highly elaborate ploy to explain the presence of a wonderbra in ancient Greece. Star Trek was a very, very happy show that inspired and continues to inspire generations of aspiring astronauts, astronomers and engineers. BSG just doesn't do that, because it's politics/angst in space and barely sci-fi at all. But hope is not lost. Dr Who is in many ways the moral heir to Trek, both in challenging social taboos and promoting how cool and shiny tech can be without anyone worrying if their toaster is actually a teenage emo psychopath.
2 : Why NASA Paid Me To Photograph A Potato
They didn't pay me very much, you understand, but it did happen. Explaining why they did this at all in the introduction spoils the fun, so go read the article. I think this probably still trumps writing a fairy tale about a princess and a magical moose as a quick start guide and various interpretative dance performances for the title of "weirdest thing my job entails".
One of those posts I can't help but think, "hmm, I thought this would be more popular than that" (96 hits !). This is, as close as possible, what the sky would look like if we could see light emitted from neutral hydrogen. Unlike most of my other recent posts, it's not overly long and it's full of pretty pictures. It uses real data, matched as closely as possible to the sky in selected locations around the world. If we could see this with our eyes, we'd never have called it space. Being able to see the sky in another wavelength, and knowing that those features are absolutely real - well, I for one think that's pretty neat.
Here's to another 200 rambling posts about astronomy ! And potatoes !
Monday, 6 April 2015
Ask An Astronomer Anything At All About Astronomy
For those who haven't been paying close attention, you might want to take a look at the new Q&A section. Here I collect the questions people have asked on the interweb which I have attempted to answer. The first batch are all those I could remember answering.
Since this is a very regular occurrence, I'll aim to post weekly updates. I only include my own answers where the alternatives provided were wrong or I felt my own answer added something useful.
For those who did notice the Q&A page, you should also notice that there's now a contents section with internal page links to each question, which is nice.
This week's additions with even more concise answers :
1) Are we sure the acceleration of the expansion of the Universe is real ?
Probably.
2) Could you pee all the way around the Moon ?
No, but you could around a 2km wide asteroid.
3) How many aliens are there ?
Fifty seven. Six. A million and two. How many would you like ?
4) Could galaxies actually be moving because space is flowing ?
No. It's not that wibbly-wobbly.
5) Is the Universe infinite ?
Could be, but I'd rather it wasn't.
6) How can we prove dark matter exists ?
We can't, yet. Lots of evidence says it exists, and direct detection experiments are underway.
7) How can we detect gravity ?
By dropping cats into a black hole, possibly with lasers. Mew mew mew !
8) What's the latest progress in detecting dark matter ?
Nothing conclusive.
9) Will NASA's pet-rock-on-a-leash need a push to keep it in orbit ?
It will need a few pushes to put it in orbit. After that it will run around in circles all day for no reason, just like a real dog.
10) Do stupid astronomy memes matter ?
Yes they do. I wish they didn't, but they do.
Since this is a very regular occurrence, I'll aim to post weekly updates. I only include my own answers where the alternatives provided were wrong or I felt my own answer added something useful.
For those who did notice the Q&A page, you should also notice that there's now a contents section with internal page links to each question, which is nice.
This week's additions with even more concise answers :
1) Are we sure the acceleration of the expansion of the Universe is real ?
Probably.
2) Could you pee all the way around the Moon ?
No, but you could around a 2km wide asteroid.
3) How many aliens are there ?
Fifty seven. Six. A million and two. How many would you like ?
4) Could galaxies actually be moving because space is flowing ?
No. It's not that wibbly-wobbly.
5) Is the Universe infinite ?
Could be, but I'd rather it wasn't.
6) How can we prove dark matter exists ?
We can't, yet. Lots of evidence says it exists, and direct detection experiments are underway.
7) How can we detect gravity ?
By dropping cats into a black hole, possibly with lasers. Mew mew mew !
8) What's the latest progress in detecting dark matter ?
Nothing conclusive.
9) Will NASA's pet-rock-on-a-leash need a push to keep it in orbit ?
It will need a few pushes to put it in orbit. After that it will run around in circles all day for no reason, just like a real dog.
10) Do stupid astronomy memes matter ?
Yes they do. I wish they didn't, but they do.
Saturday, 4 April 2015
Things That Look Like Other Things
Some potatoes look like asteroids, others look like cartoon dog bones. Some galaxies look like the Loch Ness Monster. And one comet nucleus looks a lot like a rubber duck. If there's any cosmic significance to an asteroid looking like a potato or a comet looking like a rubber duck, I should very much like to know what that is.
Which is why, when I see a meme like this one...
... there can be only one response.
It's just not even wrong. Even making the comparison is pointless. If you're of the opinion that this is harmless trivia, scroll to the end. Otherwise keep reading.
The Universe is quite a big place, and contains quite a lot of things. That some of them look like other things is as significant as the correlation between cheese consumption and the number of people who die by becoming tangled in their bedsheets. It's called a coincidence, people. When you have (literally) astronomically large numbers of objects, you're gonna get a few of those.
Let's look at each of the three comparisons in the meme, just because why not.
1) BRAIN CELL vs UNIVERSE !
I was not able to find the source of the image of the brain cell in the meme. I'm not a biologist, but since an image search for "brain cell" reveals hundreds of very similar images, I'm going to assume the image is accurate.
I already knew, however, exactly where the "Universe" image came from - the Millennium Simulation. The clue is in the name. This isn't an image of the real Universe at all, it's a simulation. And in some ways it's a very simple simulation, since the only physics involved was gravity. No gas, no stars, no complicated fluid effects, no magnetic fields. Just gravity. That's all that's needed to produce something that, for some amount of time, looks a bit like a brain cell.
Here's what the real Universe looks like... well, as close as is reasonable, at any rate (as I describe in great detail here) :
The simulation image only shows particles of dark matter. Make no mistake, the sheer number of particles (more than ten billion !) makes this an incredibly powerful simulation if you know how to use it. And it does look a lot like the observable Universe if you only count the positions of galaxies, and don't look at the details like actual images of said Universe.
That the simulation was visualised in such a way that it looks a bit like a brain cell is just not interesting - it was an arbitrary choice by the scientists to (quite correctly) make a nice image for public outreach, and show the details they were interested in as clearly as possible. That simulation was produced by only modelling gravity. And you know what - that simulation did not become conscious or do anything remotely mystical. It couldn't, because at the end of the day a bunch of simulated particles that have no property except mass can't do a lot except fall together in an interesting way.
That one component of the Universe might look a bit like a brain cell for some short (on cosmic scales) amount of time ? Big bloody deal.
2) BIRTH OF A CELL vs DEATH OF A STAR
But... but... but they don't even look the same !!!
I mean, seriously. Come on people. The cell image shows two uniform-ish spheres pulling apart. The second shows two truncated shells with bright rings at the edges and a big bright thing in the middle. Even without knowing any of the details, they look completely different ! Seriously, who looks at this and thinks, "these two completely different looking things look like the same thing" ? Aaarrrgh.
The only, marginal and completely superficial resemblance is that there are round things in both images. The only conclusion one can draw from this is that round things exist. Bubbles exist. Footballs exist. Various fruits exist. Water drops exist. Planets exist. And various parts of the anatomy exist.
Many years ago I showed the above image of the Eta Carinae nebula (associated with the death throes of a massive star) to a less-nerdy friend. Since were were both about 15 at the time, his response was inevitably "testicles in space !". Does that mean anything ? God, I hope not.
Stars are round. When they die, they sometimes produce large round structures. Who'd have thunk it.
What's really ironic about the meme is that the supernova image is actually an artists impression. So even when you compare the splitting of a cell to an idealised view of an exploding star, you find they don't look anything like each other. Amazing ! Here's what it actually looks like :
There are also quite a lot of supernovae that look even less like cell division than this one. Ironically one of those is used in the very next image.
3) EYE vs NEBULA
Lord have mercy. Not only does this fine image of the Crab Nebula make the point that star death doesn't always look like a dividing cell, but with yet more irony there are plenty of nebulae that look a lot more like the overall structure of an eye than this one. But presumably, the intention here is to compare the filamentary structure of the iris with the filaments in the nebula.
As I have made great efforts to point out, the Universe looks completely different in different wavelengths, and no particular wavelength of light is any more real than the visible light we can see with our eyes. Here's the Crab Nebula at infra-red wavelengths, as seen by NASA's Spitzer Space Telescope :
So much for filaments. But OK, there are filaments at some wavelengths. The iris, however, has a size which is controlled by muscles to vary how much light needs to be let in. So if you look again at the iris image, you'll see that the strands near to the pupil are all straight, completely unlike anything seen in the Crab Nebula. Worse, the iris is thin, whereas nebula are complex three-dimensional structures. And, as with the brain-universe, simulations of supernovae can reproduce some of the observed structures quite well based entirely on known physics, which is again completely different to the processes which create an eye.
Conclusion
Come on people. Please stop. The Universe contains hundreds of billions of galaxy filled with hundreds of billions of stars each and who-the-frak knows how many nebulae and planets and asteroids. That some of them have, at best, a marginal and temporary resemblance to everyday objects is the very definition of coincidence. Unless you think there's also a mystical significance between the apparent resemblance of a galaxy to the Loch Ness monster, or a potato to an asteroid, or a comet to a rubber ducky, this doesn't mean a darn thing. Aaargh.
The human brain has an amazing pattern-recognition ability which is genuinely very useful in astronomy. I would go so far as to say that if you can't see a pattern, there probably isn't one, and if things don't look the same, they're probably not the same. Your brain can detect stripy tigers in dark forests, which helped your ancestors avoid getting eaten. But many of them probably also saw tigers that weren't there, which didn't matter very much. So when you do see things that look like other things, you've got to be much more careful about deciding whether the resemblance is significant, merely a coincidence, or just an outright illusion.
EDIT : Of course, if all you took from the meme was, "these things look nice, and these other things look nice too", then all is well. You probably shouldn't have bothered reading this. But many people do see a deeper meaning here; presumably visual pattern recognition is not a discrete, separate part of the brain. Moreover, that the comparison is about birth, awareness and death, and is so contrived that in two cases it had to use non-real images, is very strong evidence that that was the wilful intent of the creator. At the very least, it's tough to see anyone creating this meme without being aware of how people would react.
Stupid people aren't dangerous; stupid people who spread their stupidity around are a problem.
Which is why, when I see a meme like this one...
It's just not even wrong. Even making the comparison is pointless. If you're of the opinion that this is harmless trivia, scroll to the end. Otherwise keep reading.
The Universe is quite a big place, and contains quite a lot of things. That some of them look like other things is as significant as the correlation between cheese consumption and the number of people who die by becoming tangled in their bedsheets. It's called a coincidence, people. When you have (literally) astronomically large numbers of objects, you're gonna get a few of those.
 |
| From the wonderful spurious correlations. |
1) BRAIN CELL vs UNIVERSE !
I was not able to find the source of the image of the brain cell in the meme. I'm not a biologist, but since an image search for "brain cell" reveals hundreds of very similar images, I'm going to assume the image is accurate.
I already knew, however, exactly where the "Universe" image came from - the Millennium Simulation. The clue is in the name. This isn't an image of the real Universe at all, it's a simulation. And in some ways it's a very simple simulation, since the only physics involved was gravity. No gas, no stars, no complicated fluid effects, no magnetic fields. Just gravity. That's all that's needed to produce something that, for some amount of time, looks a bit like a brain cell.
Here's what the real Universe looks like... well, as close as is reasonable, at any rate (as I describe in great detail here) :
The simulation image only shows particles of dark matter. Make no mistake, the sheer number of particles (more than ten billion !) makes this an incredibly powerful simulation if you know how to use it. And it does look a lot like the observable Universe if you only count the positions of galaxies, and don't look at the details like actual images of said Universe.
That the simulation was visualised in such a way that it looks a bit like a brain cell is just not interesting - it was an arbitrary choice by the scientists to (quite correctly) make a nice image for public outreach, and show the details they were interested in as clearly as possible. That simulation was produced by only modelling gravity. And you know what - that simulation did not become conscious or do anything remotely mystical. It couldn't, because at the end of the day a bunch of simulated particles that have no property except mass can't do a lot except fall together in an interesting way.
That one component of the Universe might look a bit like a brain cell for some short (on cosmic scales) amount of time ? Big bloody deal.
2) BIRTH OF A CELL vs DEATH OF A STAR
But... but... but they don't even look the same !!!
I mean, seriously. Come on people. The cell image shows two uniform-ish spheres pulling apart. The second shows two truncated shells with bright rings at the edges and a big bright thing in the middle. Even without knowing any of the details, they look completely different ! Seriously, who looks at this and thinks, "these two completely different looking things look like the same thing" ? Aaarrrgh.
The only, marginal and completely superficial resemblance is that there are round things in both images. The only conclusion one can draw from this is that round things exist. Bubbles exist. Footballs exist. Various fruits exist. Water drops exist. Planets exist. And various parts of the anatomy exist.
Many years ago I showed the above image of the Eta Carinae nebula (associated with the death throes of a massive star) to a less-nerdy friend. Since were were both about 15 at the time, his response was inevitably "testicles in space !". Does that mean anything ? God, I hope not.
Stars are round. When they die, they sometimes produce large round structures. Who'd have thunk it.
What's really ironic about the meme is that the supernova image is actually an artists impression. So even when you compare the splitting of a cell to an idealised view of an exploding star, you find they don't look anything like each other. Amazing ! Here's what it actually looks like :
There are also quite a lot of supernovae that look even less like cell division than this one. Ironically one of those is used in the very next image.
3) EYE vs NEBULA
Lord have mercy. Not only does this fine image of the Crab Nebula make the point that star death doesn't always look like a dividing cell, but with yet more irony there are plenty of nebulae that look a lot more like the overall structure of an eye than this one. But presumably, the intention here is to compare the filamentary structure of the iris with the filaments in the nebula.
As I have made great efforts to point out, the Universe looks completely different in different wavelengths, and no particular wavelength of light is any more real than the visible light we can see with our eyes. Here's the Crab Nebula at infra-red wavelengths, as seen by NASA's Spitzer Space Telescope :
So much for filaments. But OK, there are filaments at some wavelengths. The iris, however, has a size which is controlled by muscles to vary how much light needs to be let in. So if you look again at the iris image, you'll see that the strands near to the pupil are all straight, completely unlike anything seen in the Crab Nebula. Worse, the iris is thin, whereas nebula are complex three-dimensional structures. And, as with the brain-universe, simulations of supernovae can reproduce some of the observed structures quite well based entirely on known physics, which is again completely different to the processes which create an eye.
Conclusion
Come on people. Please stop. The Universe contains hundreds of billions of galaxy filled with hundreds of billions of stars each and who-the-frak knows how many nebulae and planets and asteroids. That some of them have, at best, a marginal and temporary resemblance to everyday objects is the very definition of coincidence. Unless you think there's also a mystical significance between the apparent resemblance of a galaxy to the Loch Ness monster, or a potato to an asteroid, or a comet to a rubber ducky, this doesn't mean a darn thing. Aaargh.
The human brain has an amazing pattern-recognition ability which is genuinely very useful in astronomy. I would go so far as to say that if you can't see a pattern, there probably isn't one, and if things don't look the same, they're probably not the same. Your brain can detect stripy tigers in dark forests, which helped your ancestors avoid getting eaten. But many of them probably also saw tigers that weren't there, which didn't matter very much. So when you do see things that look like other things, you've got to be much more careful about deciding whether the resemblance is significant, merely a coincidence, or just an outright illusion.
EDIT : Of course, if all you took from the meme was, "these things look nice, and these other things look nice too", then all is well. You probably shouldn't have bothered reading this. But many people do see a deeper meaning here; presumably visual pattern recognition is not a discrete, separate part of the brain. Moreover, that the comparison is about birth, awareness and death, and is so contrived that in two cases it had to use non-real images, is very strong evidence that that was the wilful intent of the creator. At the very least, it's tough to see anyone creating this meme without being aware of how people would react.
Stupid people aren't dangerous; stupid people who spread their stupidity around are a problem.