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Wednesday 29 March 2017

The Universe in 101 words: What's the Big Rip?

Above: A map of the web of galaxies and galaxy clusters that make our local universe.

It sounds like a fart joke. 

But this fart could end the Universe:

The expansion of the Universe is accelerating, powered by ‘dark energy’. If dark energy stays constant it will eventually pull the galaxy clusters apart – but the gravity holding the galaxies themselves together wont be overwhelmed. 

There's another scenario however, if dark energy grows with time...

The expansion of space will accelerate, until gravity can't hold the Milky Way together.

Then the Solar System will fly apart, leaving Earth alone in the darkness. 

Finally, Earth would disintegrate - down to its atoms.

That's the Big Rip.

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One by one the stars would disappear from view....

Monday 27 March 2017

The Universe In 101 Words: Rogue Black Hole Ahead!

Bad day? Any inhabitants of the galaxy pictured are getting a worse one. A black hole the size of a solar system is barrelling through it at 2000 km/s - far faster than any space ship.

How? Huge black holes result from smaller holes merging. This merger gave off massive gravitational waves, equivalent to 100 million supernova - hurling the monster hole through space.

Worlds caught in its path wouldn't see darkness approaching though - the hole's dragging clouds of superheated gas along. Instead the sky would get brighter and hotter until the very rocks boiled.

Not much better IMHO...

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Wednesday 22 March 2017

Answers for students: What are ray diagrams?

Part of a series in which I answer some of the fundamental physics questions students of all ages ask me.

What is light? Mostly you'll hear that light travels in waves. And that's true*. But it also comes in particles, called photons. And then, to make it more confusing, people talk about 'rays' of light.

Who the hell is Ray, and  what does he have to with lasers? Can he be trusted with one?

And what does he know about the missing Death Star plans!!!?

Well, I've got bad news for you: Like Death Stars, rays aren't real.... but if we're trying to calculate the path light takes, especially when we get to things like diffraction and refraction, accurately drawing waves themselves quickly gets difficult - it's all just too complicated. 
To simplify this we use ray diagrams: These aren't meant to indicate that light is made up of rays, it's just a convenient way of showing the direction of a group of waves. 

To turn a wave diagram into a ray diagram is simple: Draw a line at right angles from the line of the wave, pointing in the direction the waves is going. Like so:
This is the 'ray' associated with that wave. If the the wave front is very broad, add some more. If the wave front is curved draw your ray at right angles to the tangent of the wave, and do it at several points, like so:

...which gives you a ray diagram like this:

...and that's all a ray diagram is, a way of showing the direction of motion of the waves!

*Light can also be a particle, and can morph from particle to wave... but that way lies quantum mechanics, and I've had enough headaches today.

Monday 20 March 2017

4 Crazy ways of getting into space - that might actually get built:

The Rocket-Balloon*:

Above: The rocket stage of a rocket-balloon (called the Bloostar) pulls away from its balloon stage.

The idea of crossbreeding a balloon with a rocket sounds like madness doomed to end in a fiery explosion on a spectacular youtube video.

But the idea has been around since the 1950's. To get to space a rocket must first punch through the Earth's atmosphere, which eats up a lot of extra fuel. So why not float the rocket to the top of the atmosphere on a balloon?

Well, partly because that makes the rocket incredibly hard to steer, and partly because a rocket big enough to launch a useful satellite would need a balloon that was unfeasibly huge. One snapped cable and someone could be getting a fully fuelled space rocket through the roof of their house.

This, of course, hasn't stopped people doing it: Sub-orbital sounding rockets, carrying simple and lightweight sensor packages, were launched in the 1950's

And that was as far as the rocket-balloon got, until the turn of the millennium when miniaturisation started to work its way into satellite technology. Today a useful space satellite can be small enough to hold in you hand, and the rocket needed to put it into orbit can be not much bigger than a 1950's sounding rocket. The Spanish company Zerotoinfinity have developed a commercial rocket-balloon launcher for small satellites called the Bloostar, and have just had a successful test firing at altitude - commercial flights could start as soon as next year.

Space cannons:

Above: A rare image of the HARP space cannon firing. Bits of this behemoth gun can be found rusting on the island of Barbados today.

H.G Wells wrote about a cannon big enough to blast a projectile into space, and all the way to the Moon. 

Which is insane, right? I mean, such a cannon would need to be many times the size of the biggest naval cannons, and the shock waves from it would shake buildings apart...

...Enter the US military.

In the 1960s the US army and Canadian ballistics expert Gerald Bull led a project that built, tested, and fired space cannons, sending sensor packages and test payloads well above Earth's atmosphere and into space. Despite their success, the project was scuppered by the space explorer's old nemesis, politics. 

From there the story takes a much darker turn: Gerald Bull turned to advanced weapons manufacture to keep funding his research - sort of like a reversed Tony Stark - and ended up facing a professional assassin in a hotel corridor

You can read the full, tragic, story here.

Ride a laser beam up the rear:

Above: An infographic explaining one variant of the 'lightcraft' idea.

Space travel is fairly risky to start with, so you'd think that shooting a high powered laser at a spaceship while it flew wouldn't be a good idea. I work with industrial cutting lasers professionally, so I can confirm that it's a very bad idea - I've seen how little respect a powerful laser has for solid steel.

It's such a bad idea that it's actually the basis of some novel anti-missile weapons.

But... a rocket, a long tube of highly flammable stuff with an explosion at one end, ain't that safe either hombres. So how do you turn a laser into a rocket?

You attach a curved mirror to the base of your rocket, and fire a powerful laser  at it. The mirror focuses the laser light to a point just beneath the rocket, which forces the air there to rapidly expand, producing thrust. If you need it to work in space, you can have the rocket expel material into the laser's focus.

The huge advantage of this is that the rocket is fuel free - the electricity for the laser can be taken from the national grid even. The down side is that you are, as I mentioned, shooting a powerful laser at your spaceship. 

Surprising, then, that people have very seriously looked at a laser propelled manned vehicle.

The technology is still a very long way from being mature, but it might do a lot more than just launch satellites. Laser based tractor beams are one of the technologies space agencies are seriously looking at to defend Earth from a major asteroid strike.

Climb a magic rope: 

Above: A car climbing a space elevator cable.

Rope is wonderful stuff, but most ropes aren't so wonderful that they'll get you into space. 

That could change, however: where most people would shrug and go 'eh, rope's just rope' scientists and engineers went 'we shall build a rope all the way into space'! 

Because... well, because a great many of us are a wee bit crazy.

Even so, the basic 'climbing rope to space' idea has spawned a host of daringly edge-of-what's-possible high-tech-rope based ways into space.
  • Probably the best known is the brain melting space elevator, a cable car into space thousands of kilometres long, anchored at one end to a huge geostationary satellite  and to a mega-mega skyscraper on the ground end. But there are other equally zany designs for ropes into space.
  • The rotating orbital tether: This is a big, spinning, bit of high strength space rope. As it whirls around the lower end grazes the upper atmosphere, striking just deep enough for a sub orbital spacecraft (like Virgin Galactic's SpaceShipTwo) to hook on to it and be flung into deep space.
  • Endo atmospheric tethers: This tether is run behind a high altitude aircraft, and grabs a small, lightweight, launch vehicle. The tether, and the difference in momentum between the big heavy plane and the lightweight launcher propels it to hypersonic speeds.
All crazy as a spoon... yet space agencies have been quietly working on tether technologies for decades...

* Yes there's a condom joke there if you're determined to find it. I'm not, but feel free.

Wednesday 15 March 2017

The Universe in 101 words: How far away is Voyager 2?

Above: A breakdown of the 'famous inscription on Voyager 2, designed to tell any intelligence that might find it who we were, and where we came from.

It's amazing what persistence can do. Take the Voyager 2 space probe: After 40 years of flying even light, the fastest thing there is, would take nearly a day to reach it (you can actually track it in real time here).

So it's dark where Voyager is now, punctuated only by the glow of the Milky Way, and the distant point that is the Sun.

But it isn't empty.

Voyager still talks with Earth - it's exploring the dust, gas, and strangely behaved magnetic fields in that darkness. Over millions of years they can slowly influence our planet, even causing mass extinctions.

Tuesday 14 March 2017

The Universe in 101 words: Should we look for life in the asteroid belt?

Look at where NASA sends its missions and one world stands out: Mars.

Why? Mars may hold The Big Discovery - alien life (however humble). But what if Mars isn't, after all, the best place to look?

The dwarf planet Ceres, in the asteroid belt,  has had the ingredients of life - liquid water and carbon chemistry - near its surface geologically recently*. It's gravity is far lower than Mars, a major advantage if you want to collect samples from it, nor does it have Mars´ deadly weather. 

Perhaps its time for a lander to Ceres...

*So not at all recently, but not so mind buggeringly long ago as a lot of the things in the universe.

Wednesday 8 March 2017

Answers for authors: What would life be like around TRAPPIST-1?

A tiny star 40 light years from Earth, called TRAPPIST-1*, made some major waves recently: It has seven planets, all roughly the same size as Earth, all with some chance of habitable conditions.

Above: An artists impression of the TRAPPIST-1 solar system.

So the question has been asked: If a civilisation were located on one of the TRAPPIST-1 planets, what would be different to our civilisation?

Short answer? A lot. 

Long answer?
First lets look at the TRAPPIST-1 star itself. It's an ultra cool red dwarf, the smallest kind of true star** you can get - just 8% the Sun's mass, and barely wider than our planet Jupiter. That gives it a very different look to our Sun: In a nearby planet's sky it would appear orange coloured, and dimmer. Paradoxically, if you're viewing from a habitable world, it would also look slightly bigger as a red dwaf's habitable zone is much closer in than  our Sun's. Red dwarfs also suffer from huge star spots, giving it a mottled look- and these come as part of more of a violent side: TRAPPIST-1 spits out powerful particle storms, and a lot of UV and X-ray radiation.  Although invisible except to specialised instruments, coronal mass ejection particle storms (responsible for auroras on Earth) damage the electronics of satellites and spacecraft, cause cancers in astronauts, and cause radio blackouts and damaging power surges here on Earth. Those from TRAPPIST-1 would hit its planets like the strongest storms ever spat out by our Sun.

But being dim, orange, angry, and ugly is no obstacle to success - look at Donald Trump. Being so small means TRAPPIST 1 burns its nuclear fuel much more slowly and efficiently than our sun, so it will live thousands of times longer.  

I truly hope the Trump doesn't live thousands of times lomger than expected . Though he is full of surprises... horribly full of them...

So that's TRAPPIST-1 itself: Small, orange, angry, and tenacious. What about the planets around it? 

There are seven of them and, because such a small star only has small gravity, they must orbit much closer than any of our planets to stay bound.  The furthest of them still has an orbit much smaller than Mercury's. But the cool stars small size means these worlds don't scorch - that outermost world is probably an ice ball! The habitable zone, where planets are most likely to have liquid water, is closer still - three of the planets are in it. 

So, making the assumption that any civilisation will be based on one of the habitable zone planets, we can come to a few conclusions: 

  • The Sun will look orange, bigger in the sky than ours, and dimmer to look at. There aurora will be spectacular - assuming the planet has a strong protective magnetic field. 
  • If the planet doesn't... the very powerful, close range, solar storms will have damaged and thinned the atmosphere, leaving it more like a big version if Mars than Earth.  
  • The year will be a couple of weeks long at the most - if the planet has seasons each would only last a couple of days. 
  • These planet's close range to their sun might make them 'tidally locked' - so one side  always faces the sun, and one side always faces away. That would make the sun stand still in the sky, bathing half the planet in eternal day, and the other half in eternal night. A thick atmosphere  will balance the extreme temperature  differences out a bit, but one side would still be a place of bitter cold and ice caps,the other a realm of deserts.  Only a strip of the planet along the day/night boundary would be temperate,  limiting the civilisation's ability to spread. 
  • Because of this solar system's  small size the other planets would look much bigger in the sky than the planets of our solar system - often bigger than the moon from Earth. So if more than one planet had a civilisation each could see the glow of each other's city lights at night. 
  • Plantlife would be a different colour from Earth's: Our plants are green, because that's the brightest colour in the Sun's spectrum (see 'what colour is the Sun'), and the plants need to reflect the brightest light to avoid cell damage. But a red dwarf's light is fainter, so plants on a TRAPPIST 1 planet might well be black, to absorb as much as possible .
  •  The sky would also be a different: Our sky is blue thanks to scattered blue light from the Sun, which TRAPPIST 1 produces less of - so it's sky would be much darker. Since the blue wavelengths  are absent the sky might even be green, as that colour is the more abundant wavelength short enough to scatter off air molecules.
What about travel between those planets? The orbits of these worlds are the same sort of distance apart as the Earth and Moon (which are only three days travel apart using 1960's rocket technology).  Because the orbits are so short launch windows would occur on a weekly basis... Which makes the TRAPPIST 1 solar system sounds like an ideal place for a spacefaring civilisation.

It's not that we're complaining about how hard space travel is universe... well... actually it is.

But this teeny star system also has hazards - the planets will need heavy duty magnetic fields to protect them from their ill tempered sun,  and some radiation will get through anyway.  A surface civilisation will need to be very X-ray tolerant. On top of that, the closeness of the planets means they tug on each other gravitationally, changing each other's orbits over millennia and causing huge climate shifts.

So, to sum up? A civilisation around TRAPPIST 1 would be able to travel between the worlds there in days, and their seasons would race past in mere days. The plants would be orange (assuming they worked the same way as ours), and the sun would be distinctly orange in the dark sky, and would look larger than ours, and the other worlds would loom in the sky, as big as the Moon looks from Earth. But they will need to be hardy: Only thin strips of their worlds, along the terminators, would be habitable - the rest of their surfaces will be gripped in eternal roasting day or endless freezing night. Radiation levels will be high, with frequent  solar storms powerful enough to cause worldwide radio blackouts, power grid surges, a severely damage satellites. Humans would face elevated cancer risk, even on the ground, and in space a storm could be lethal.

A fascinating setting - but not for the fainthearted...

*Named after the beer brewed by Trappist monks . NAMED AFTER BEER! 
*A true star fuses hydrogen for fuel. Objects much smaller than TRAPPIST-1 can only fuse deuterium, and are called 'Brown dwarfs'.

Monday 6 March 2017

Answers for students: What links electromagnetic waves and ickle fluffy ducks?

This post is part of a series answering some of the physics questions students ask me most often.

What do waves have to do with radiation? 
the short answer is 'everything', but that wont help in an exam. 

The long answer?

Well.... look at this bridge.....

Above: Watch a bridge fall down because of standing waves. Go on, everyone likes seeing big thngs fall down.

Did you watch up to the bit where the man smoking the pipe rescues the dog? 
How about the bit where the bridge fell down? That's the important bit (although the dog rescuer was my favourite bit). 

This is what happens when you build a bridge without taking into account the way strong winds can resonate with the structure and cause standing waves: The wind blows just right one day and....

But I'm getting ahead of myself: Before we can collapse bridges with waves* we need figure what waves actually are (and how they relate to radiation)....

So let's start smaller, with a cat in a boat on a really still lake (stay with me, this will go somewhere). The cat is watching a tasty looking duckling swimming a meter away from the boat. Luckily for the duckling cats don't much like water, and all the cat can do is pace frustratedly back and forth inside the boat..

Frustration thy name is hungry cat in a boat watching a passing duckling. Boy you have a long name, stick to frustration. Image by K.J. Rogers

The cat's pacing makes the boat bob up and down, sending waves towards the duckling. When the waves hit the duckling they make it bob up and down. 

This is the odd bit: Obviously the boat bobbing up and down has moved the duckling - but I water has passed from the boat to the duckling.

Think about that: Even though the waves have moved from boat to duckling, the water hasn't: If you shot the duckling with a water pistol then (I'm not suggesting that's the kind of thing you'd do, although you could be anyone, so you might) the force of the water would push the duckling sideways.....

Really? Could you really shoot the ickle fluffy duckling? If you could, have you considered a career as a London city banker?

.....but when the waves hit the duck it just moves up and down -  so the waves haven't actually carried any water sideways from the boat**, they've just carried the up and down motion.

If that's not too clear to you (and, for a long time it was as clear as mud to me), watch these ducks, and see how their position relative to the shore hardly changes as the waves strike them - they move up and down a lot but hardly move towards the shore at all, even though the waves are definitely moving that way:  

Above: Ducks bobbing in the waves - ducks are more insightful than you might think.

So, if the water hasn't travelled, then what is it that has moved from the boat and made the duckling bob up and down? 

The answer is in the question: The duck has moved up and down, so what has travelled from the boat must be the up and down motion (called an oscillation) itself - and it has done that independently of what direction the water is moving (or not moving)! A motion that travels without the thing it's moving in travelling with it seems like an odd concept - the bounce on a bouncing ball doesn't run off to the shops on its own - but if you've ever been part of a Mexican wave at a football match you've taken part in exactly the same thing: Each person just stands up and sits down a moment after the person next to them does - they don't run around jumping up and down. Yet the overall effect is definitely a moving wave:

Above: A huge Mexican wave. If you're gonna put a Mexican wave in your blog, go big or go home, that's what I've always said. But I am a bit odd.

With a bit of deduction we can go further, and suss out something general about waves: To make the duckling move takes energy, like any motion takes, so the wave must be moving energy from the boat to the duckling. 

And that's the key thing that tells us what all waves really are: They're down to energy being transmitted through whatever medium the wave is in, as an oscillation (of some kind) without actually moving that medium itself (or at least not moving it in the direction the wave is going). 

What does that have to do with radiation?

Of all the kinds of radiation there are (and the word radiation is often used to include fast moving particles) they're all down to energy being transferred from one place to another - and to do this nature uses moving oscillations - waves! For electromagnetic radiation - which means radio waves, microwaves, terahertz waves, infra red waves, visible light, UV waves, X-rays and gamma rays - the waves are oscillations in electric and magnetic fields.  Other kinds of waves (like sound waves) aren't often called 'radiation', but they still work on the same principles, and 'radiate' energy away from their source. Recently you may well have heard of newly discovered 'gravitational waves' which are a moving oscillation in space itself.

But, sticking to electromagnetic radiation for now: what type you have depends on its wavelength and frequency (the two are related, and we'll get to that in a later post), and if you arrange the different electromagnetic radiations by wavelength you'll get an electromagnetic spectrum. 

Above: The EM spectrum. Yes, visible light is just that tiny little bit of it. Yes, that does mean you can't see 99% of what goes on in the universe. Yes that's a perfect excuse to ask for infra red night vision for next Christmas. Ask Santa to get me a set too, while you're at it. Courtesy of Lumanix.

The colour of visible light depends on its wavelength, and if you keep dialling the wavelength up or down you move to a different kind of radiation.... so the differences in types of EM radiation can be thought of as really extreme kinds of colours - too extreme for our eyes to see. For example: the human eye sees light with  a wavelength of 660 nanometers as red (one nano meter = 0.000000001 meters), and 550 nanometers as green. 350 Nanometers is UV light, too short to be seen by the human eye (bees can see it though) but detectable to our skin, which turns tanned in response to it. 1500 Nanometers is infra red, too long to be seen, but we can sense it as heat (and some snakes, fish, and predator can sense it well enough to hunt by it).

Above: The main features of a simple wave, sometimes called a sine wave - because it's an idealised wave that matches very closely to the sine and cosine waves you've probably learned about in Maths.

So all waves, across the universe, are nature's way of moving energy about without having to move matter. Radiation (or at least one very common type of it called electromagnetic radiation) is made of waves moving through electrical and magnetic fields

Suggested activity:

Feel like investigating waves in class? This is a way of making nice controllable waves out of sweets. Science you can eat!


1: Why does a cork on the sea bob up and down with the waves, but not move sideways or forwards/backwards with them?

2: When a wave is generated by something moving, what is it that the wave is carrying away from the movement that generated it?

3:  Light and radio waves are closely related. State two similarities, and one difference between them.

Answers here.

* A good physicist is 50% supervillian

** If you get really big waves, or waves breaking on the shore, things are more complicated, but that's a discussion for another post.