- Email: [email protected]
Kitchen sink experiment simulates exotic white holes
For daily news stories, visit www.NewScientist.com/news
To understand white holes, go to your kitchen sink EXPENSIVE particle colliders are not the only way to explore far-out physics. It seems that water gushing from a tap and hitting a sink behaves like a white hole – the theoretical opposite of a black hole. A black hole is a dense concentration of mass surrounded by an extremely powerful gravitational field. Nothing that falls within a certain radius surrounding it, known as the event horizon, escapes. A white hole is the opposite: its event horizon allows things to escape but prevents anything from entering. However, so far white holes only exist in theory, so cannot be studied observationally. When water hits the bottom of a sink, it flows outwards in all
directions. At a certain distance from the point where the water hits the sink, the outgoing liquid rapidly decelerates and piles up before continuing its outward flow, creating a ring-like ridge. Physicists have previously suspected that any ripples that might arise beyond the ridge and travel towards it should not be able to get past the ridge. This is because at the ridge the water flows outwards at the maximum speed that ripples could travel inwards, so the ripples would make no forward progress, like a runner on a treadmill. This makes the ridge behave like a white hole event horizon. Now this has been experimentally confirmed by Germain Rousseaux
Can you make city life better? The deadline for the Philips Livable Cities Award is 28 October 2010. So if you have an idea that could improve the health and well-being of city-dwellers, now is the time to enter. Philips is offering €75,000 to turn one winning idea into reality, plus €25,000 each for two runners-up. KaBOOM! shows how a great idea can really take off. This independent non-profit organization wants all US children to have space and time to play. It brings local communities together to build playgrounds, and so far has created more than 1800 of them. Its Playful City USA program requires cities to focus on their play infrastructure and this year 118 have joined. The organization then compiles cities’ best ideas and shares them with mayors across the country. By empowering communities, KaBOOM! is creating healthier, happier children, greener cities and stronger neighborhoods.
To enter the Philips Livable Cities Award or to find out more about it, please go to www.philips.com/because.
of the University of Nice in France and colleagues. Instead of looking at water hitting a sink, the team examined what happens when a stream of viscous oil hits an empty aquarium. When they placed the tip of a needle in the path of the oil as it spread out from the collision point, it generated a v-shaped disturbance. The angle of the v depended on the relative
“The experiment is based on a simple idea everyone can understand and try at home” speeds of the fluid and any ripples on its surface. When the team measured it, they found that the two speeds are indeed equal, preventing ripples flowing in and creating something akin to a white hole event horizon. They also found that between the collision point and the ridge,
the oil flowed faster than the ripple speed, causing any ripples arising there to be swiftly carried outwards – just as things inside a white hole should get spat out (arxiv.org/abs/1010.1701). “The experiment is based on a simple idea everyone can understand and try at home,” says Ulf Leonhardt of the University of St Andrews, UK. Daniele Faccio of Heriot-Watt University in Edinburgh, UK, who recently used lasers to simulate an event horizon, says studying black and white hole analogues could provide insights into the physics of these exotic objects. For example, in 1974, Stephen Hawking showed mathematically that event horizons should radiate light. Our telescopes are not sensitive enough to confirm this, but analogue experiments like Rousseaux’s could help reveal the physical mechanism for the radiation, which remains unclear. David Shiga n
L c ast to hanc en e te r!
To understand white holes, go to your kitchen sink EXPENSIVE particle colliders are not the only way to explore far-out physics. It seems that water gushing from a tap and hitting a sink behaves like a white hole – the theoretical opposite of a black hole. A black hole is a dense concentration of mass surrounded by an extremely powerful gravitational field. Nothing that falls within a certain radius surrounding it, known as the event horizon, escapes. A white hole is the opposite: its event horizon allows things to escape but prevents anything from entering. However, so far white holes only exist in theory, so cannot be studied observationally. When water hits the bottom of a sink, it flows outwards in all
directions. At a certain distance from the point where the water hits the sink, the outgoing liquid rapidly decelerates and piles up before continuing its outward flow, creating a ring-like ridge. Physicists have previously suspected that any ripples that might arise beyond the ridge and travel towards it should not be able to get past the ridge. This is because at the ridge the water flows outwards at the maximum speed that ripples could travel inwards, so the ripples would make no forward progress, like a runner on a treadmill. This makes the ridge behave like a white hole event horizon. Now this has been experimentally confirmed by Germain Rousseaux
Can you make city life better? The deadline for the Philips Livable Cities Award is 28 October 2010. So if you have an idea that could improve the health and well-being of city-dwellers, now is the time to enter. Philips is offering €75,000 to turn one winning idea into reality, plus €25,000 each for two runners-up. KaBOOM! shows how a great idea can really take off. This independent non-profit organization wants all US children to have space and time to play. It brings local communities together to build playgrounds, and so far has created more than 1800 of them. Its Playful City USA program requires cities to focus on their play infrastructure and this year 118 have joined. The organization then compiles cities’ best ideas and shares them with mayors across the country. By empowering communities, KaBOOM! is creating healthier, happier children, greener cities and stronger neighborhoods.
To enter the Philips Livable Cities Award or to find out more about it, please go to www.philips.com/because.
of the University of Nice in France and colleagues. Instead of looking at water hitting a sink, the team examined what happens when a stream of viscous oil hits an empty aquarium. When they placed the tip of a needle in the path of the oil as it spread out from the collision point, it generated a v-shaped disturbance. The angle of the v depended on the relative
“The experiment is based on a simple idea everyone can understand and try at home” speeds of the fluid and any ripples on its surface. When the team measured it, they found that the two speeds are indeed equal, preventing ripples flowing in and creating something akin to a white hole event horizon. They also found that between the collision point and the ridge,
the oil flowed faster than the ripple speed, causing any ripples arising there to be swiftly carried outwards – just as things inside a white hole should get spat out (arxiv.org/abs/1010.1701). “The experiment is based on a simple idea everyone can understand and try at home,” says Ulf Leonhardt of the University of St Andrews, UK. Daniele Faccio of Heriot-Watt University in Edinburgh, UK, who recently used lasers to simulate an event horizon, says studying black and white hole analogues could provide insights into the physics of these exotic objects. For example, in 1974, Stephen Hawking showed mathematically that event horizons should radiate light. Our telescopes are not sensitive enough to confirm this, but analogue experiments like Rousseaux’s could help reveal the physical mechanism for the radiation, which remains unclear. David Shiga n
L c ast to hanc en e te r!