FWIS3

vendic wrote:

Mathematicians say that they have solved a major, decades-old problem in geometry: how to reconstruct the inner structure of a mystery object ‘X’ from knowing only how fast waves travel between any two points on its boundary.

http://www.nature.com/news/long-awaited ... 1508_RHBox

For me? I confess, I don't understand the discovery. Geologists have long used seismic wave travel time to discern something of the earth's interior structure, so if this is more than that, awesome. But I don't understand it.

Well, I figured you're the geologist you might be interested.

I'll see if I can get this right.

Mathematically they have now worked out a way to determine the structure of a solid object using two surface sensors and analyzing the wave forms. So what they are saying (if I read it correctly) is that by analyzing the sensor data they can derive the "complete" or near as given the resolution and sensitivity of the sensors, the internal structure of the Earth. So it's similar to what has been done before but it goes way deeper and covers the whole globe rather than just the parts between two points as typical sonar setups do.
I have no idea how they can do this with two sensors on a 3D object so I'm either reading it wrong or am ignorant about some aspect of the findings. Or both. lol

I would imagine its all to do with tracing multiple waves over time and analyzing both the time, phase and amplitude variations to come up with an accurate 3D representation. Implementation might be tough as signals drop in amplitude and I have no idea what physical sensors are capable of resolving to with today's technology.


To be honest, I was hoping someone might be able to explain it to me

I think they've already known how to do that, but now someone came up with a mathematical proof that a specific model is accurate in modeling it. Now, if only the earth was a perfect sphere and it had perfectly concentric spheres inside it...

vendic wrote:So it's similar to what has been done before but it goes way deeper and covers the whole globe rather than just the parts between two points as typical sonar setups do.

...

To be honest, I was hoping someone might be able to explain it to me

The existing technology isn't sonar. Geologists (geophysicists to be precise) use seismograph data from big seismic events (earthquakes mostly but it was also done with nuclear bomb explosions) to analyze the structure of the interior, right down to the earth's core. The two principles are refraction and reflection of waves and wave travel time through various densities of rock. You take the seismograph data from all points on the earth and plot ground motion characteristics and wave arrival time. With the proper computer modeling, you get a good idea of the various layers of the earth. With big earthquakes, the earth will actually 'ring' as the seismic waves bounce around for a while.

I have no idea what this discovery adds to that. Good luck finding someone to explain it. Maybe someone over at Cosmoquest.

Well there you go. I learnt something new. lol