Wave-generated 'white hole' boosts Hawking radiation theory: research

Jan 18, 2011

A team of UBC physicists and engineers have designed a experiment featuring a trough of flowing water to help bolster a 35-year-old theory proposed by eminent physicist Stephen Hawking.

In 1974, Hawking predicted that black holes--often thought of having gravitational pulls so strong that nothing escapes from them--emit a very weak level of radiation. According to the theory, pairs of photons are torn apart by a black hole's gravitational field--one photon falls into the black hole, but the other escapes as a form of radiation.

In results outlined in the latest issue of , a team of UBC researchers led by international postdoctoral researcher Silke Weinfurtner put the test to Hawking's theory by creating a 'white hole' in a six-metre-long flume of flowing water.

Placing an airplane wing-shaped obstacle in the path of the flowing water created a region of high-velocity flow which blocked surface waves, generated downstream, from traveling upstream. The obstruction simulated a white hole, the temporal reverse of a black hole.

The shallow surface waves divided into pairs of deep-water waves, analogous to the photon pairs featured in Hawking's theory. Like in , they showed that the analog would also emit a thermal spectrum of radiation.

"While this creative simulation obviously doesn't prove Hawking's theory, it does show that his ideas apply broadly," says UBC William Unruh, part of the team which included European Union Marie Curie Fellow Weinfurtner, undergraduate student Matthew Penrice, Civil Engineering post doctoral fellow Edmund Tedford, and Canada Research Chair in Environmental Fluid Mechanics Gregory Lawrence.

"This experiment also exemplifies all of the strengths of UBC's research enterprise--the involvement of students, our international outreach and connections, and a very open, collaborative way of looking at scientific questions," says Unruh.

Explore further: Exploring X-ray phase tomography with synchrotron radiation

More information: Physical Review Letters paper: prl.aps.org/abstract/PRL/v106/i2/e021302

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User comments : 13

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2.3 / 5 (6) Jan 18, 2011
1 / 5 (2) Jan 18, 2011
We should now check with our most powerful telescopes a nearby black hole for a specific kind of radiation leaking from it. (what kind i don't know what ever kind they were talking about.)
1 / 5 (1) Jan 18, 2011
What the hell was this?
1.7 / 5 (6) Jan 18, 2011
This my friend is SCIENCE!... No not really, got to love how an article discredits itself half way through. "While this creative simulation obviously doesn't prove Hawking's theory"

Essencially they stuck a model plane wing in a bathtub, threw on some sciency words and hit publish.
1 / 5 (2) Jan 18, 2011
I really am not sure what they're getting at. They've painted a completely fuzzy picture in my head. Since I'm rooting for Hawking radiation, I'm glad that they didn't disprove it.
1.7 / 5 (3) Jan 18, 2011
The linked abstract and synopsis make it a little clearer. I'm not going to try and explain it myself, but I think I get what they're saying. A couple of diagrams would have helped, took me a few minutes to visualise the setup.
3.8 / 5 (4) Jan 18, 2011
What the hell was this?

This was AWESOME! It is totally true! When you catch a wave and cover a subsurface impediment (rock) you totally go faster, and that is HOT!

It could only be a clearer generalization of Hawking radiation if it involved gravity, quantum effects, photons, relativity, or really anything else at all related to Hawking radiation besides waves.
1 / 5 (1) Jan 18, 2011
Good point Pyle. They could only have made the example clearer if they used any other example. Heh.

TehDog, I read the abstract and I still don't follow. It's actually funny to me that a water example is harder for me to mentally picture than anything I've read so far in quantum physics. I can (no joke) more easily picture a fourth spatial dimension, than picture what they're talking about.

I'm glad it's not just me alone here.
1 / 5 (2) Jan 18, 2011
What the hell was this?

They got the water moving faster than the speed of sound in water (just as in a black hole space flows faster than light) and watched how waves interacted with it.
4 / 5 (4) Jan 18, 2011
We should now check with our most powerful telescopes a nearby black hole for a specific kind of radiation leaking from it. (what kind i don't know what ever kind they were talking about.)

I believe it's thermal radiation. The problem with detecting Hawking Radiation is that it's very, very faint, and black holes tend to surround themselves with matter and other radiation. That's what makes this experiment so interesting.
3.7 / 5 (3) Jan 18, 2011
Ah, found some more background on this I think.
ht(you know what to do)p://iopscience.iop.org/1367-2630/12/9/095018/fulltext
Mostly way over my head, but hopefully some of it will sink in :)
1 / 5 (3) Jan 19, 2011
Uh, How is this different from a Venturi effect?


Or Bernoulli's principle?

not rated yet Jan 19, 2011
What the hell was this?

My thought exactly.

The analogy between water waves and gravity waves seems rather...tenuous.

Paljor: The paper has this to say about your question:
Unfortunately, the question of whether black holes really radiate does not seem to be amenable to experimental investigation, because such radiation would be completely swamped by the cosmic microwave background.

...upon delving into the paper (no, I didn't understand it fully, either) there seems to be some correlation in the mathematics involved.