Science Questions

[Lord Chrusher]

Gravity is by far the weakest of the fundamental forces so it would be a poor choice to confine antimatter. We can also currently create manipulate electromagnetic fields far more easily than gravitational ones. I find a compact and energy efficient Penning Trap to be far more plausible than gravitational confinement.

[Smeghead]

Good point

[Master Gunner]

Actually, that brings a question to mind. I saw on the Wikipedia page that lasers are sometimes used to cool ions in penning traps. So... how do photons interact with antimatter? Do photons have their own anti-particle?

[Lord Chrusher]

Photons are their own anti-particles. Photons interact with anti-particles the same way as particles.

Being massless bosons, photons behave quite differently compared to the massive fermions (electrons, protons and neutrons) that make up the visible universe.

[Lord Chrusher]

So today had big SCIENCE news:

Gravitational waves, a black hole-black hole binary and a black hole merger were all observed back in September by the LIGO experiment.

This is likely the biggest discovery in physics in the last couple decades.

[My pseudonym is Ix]

I am SO HYPED. Relativity suddenly got a rocket boost and cosmology just got way more interesting.

I also am totally in love with the fact that the apparatus used to prove the existence of gravitational waves used pretty much the same layout and principles (albeit substituting masses for light sources) as the experiment that ultimately disproved the existence of the aether at the beginning of the last century. Physics comes full circle it seems, except this time we got the answer we were expecting.

[Merrymaker_Mortalis]

Gravity waves. Is that when the distances between matter varies? I.E. a gravity wave travelling through a road means the road will for a moment be a smidgen longer than normal?

[hacofo]

First the Higs now this.
The last years have been good ones.

@Merrymaker:
As far as I understood it that is the core concept, but since they are waves the road would be fluctuating between longer and shorter.
Somewhere around the width of a proton.

[Merrymaker_Mortalis]

I remember seeing a documentary that sounded like gravity waves and I thought it was, terrifyingly amazing and mind exploding.

[Dutch guy]

Gravity waves. Is that when the distances between matter varies? I.E. a gravity wave travelling through a road means the road will for a moment be a smidgen longer than normal?

Pretty much, though in this case there are 2 roads, each about 3 km long which lengthen and then shorten about the width of a proton as the wave passes.

I am in awe of the data processing and measuring equipment mostly. The signal is absolutely TINY and well below the noise floor. Being able to filter it is an achievement on it's own.

[Lord Chrusher]

Actually the changes in length are more than a thousand times smaller than the size of a proton. An analogy is measuring differences in the distance between the Sun and the nearest star to within the width of a human hair.

To be a bit pedantic for a moment, gravitational waves are not the same things as gravity waves. Gravitational waves are ripples in spacetime while gravity waves occur on the surfaces of fluids when the force returning the fluid to equilibrium is gravity. An example of gravity waves are normal ocean waves.

[Dutch guy]

I thought the measured strain as a result of the wave passing was in the order of 10^-21 so over a length of 3 km the "deflection" would be in the order of 10^-18 (ie, aprox. a proton)? I must admit I haven't had the time to read the actual paper yet.

[Lord Chrusher]

Protons are about 10^-15 metres in size. Also LIGO has 4 km long arms; VIRGO, the European gravitional wave instrument, has 3 km long arms. Once VIRGO goes back on line later this year, it will be used with the two LIGO instruments to better observe gravitional waves. One of the main improvements of using three instruments is that you will be able to determine where gravitional waves are coming from much more accurately.

[Dutch guy]

Protons are about 10^-15 metres in size. Also LIGO has 4 km long arms; VIRGO, the European gravitional wave instrument, has 3 km long arms. Once VIRGO goes back on line later this year, it will be used with the two LIGO instruments to better observe gravitional waves. One of the main improvements of using three instruments is that you will be able to determine where gravitional waves are coming from much more accurately.

Ahh, ok, missed a few zeroes then

[Dutch guy]

Not really a question but might interest some people. Came across this article just now, and it surprised me: http://mosaicscience.com/story/medicine ... em-placebo

Apparently it's possible to influence the immune system through the placebo effect and pavlovian conditioning.

[fantôme]

I was reading a thing about Pythagoras and a discovery of his that I find kind of beautiful:

Two copies of the same string (plucked, bowed or hammered), subject to the same tension, make tones that sound good together when their lengths are precise ratios of whole numbers. ie. A ratio of 1:2 forms an octave, 2:3 a dominant fifth, 3:4 a major fourth.

Furthermore, tones are in harmony if the tensions in the strings are ratios of squares of whole numbers.

Is there an explanation or theory for why there is a connection between precise ratios of numbers and sounds that are pleasing to the human ear?

[Sethlock]

This paywalled http://journals.aps.org/prl/abstract/10 ... 107.108103 article has a theoretical model, but I don't know if its actually been tested.

Imagine that when hearing a sound, two separate neurons respond to two different tones. If stimulated they each fire, and a third neuron is stimulated before passing the final signal along to the brain. In their model, this third neuron fires if either or both neurons are stimulated. If the tones heard are consonant the two signals would arrive at the 3rd neuron at the same time, and it fires once. If dissonant the third neuron fires twice. The former leads to a constant stream of regular pulses, vs unevenly spaced pulses in the latter.

Again, I didn't find anyone having tested this outside a mathematical model

[Darkflame]

I was reading a thing about Pythagoras and a discovery of his that I find kind of beautiful:

Two copies of the same string (plucked, bowed or hammered), subject to the same tension, make tones that sound good together when their lengths are precise ratios of whole numbers. ie. A ratio of 1:2 forms an octave, 2:3 a dominant fifth, 3:4 a major fourth.

Furthermore, tones are in harmony if the tensions in the strings are ratios of squares of whole numbers.

Is there an explanation or theory for why there is a connection between precise ratios of numbers and sounds that are pleasing to the human ear?

Doesn't explain everything, but explains A LOT :
https://www.youtube.com/watch?v=i_0DXxNeaQ0

Theres a crazy cool demo of a audio illusion there too.
Very worth watching. (as is most of her stuff)

[fantôme]

Thank you both for the replies, it is making sense to me now.

Also thank you for pointing me towards that YouTube channel, its brilliant.

[JustAName]

Oh yeah, Vi Hart is so rad.