Ask any question you want about Physics

a reply to: Phage

University of Minnesota engineers make sound loud enough to bend light on a computer chip

a reply to: darkorange

so that would mean that light IS affected by gravity.

That depends upon your frame of reference.

And why everyone is looking for graviton as gravity carrier force when it is just topological curvature?

Who is everyone? In any case, finding evidence for gravitons would throw a monkey wrench into general relativity which would be a big deal. Physicists like making big deals. Messing up general relavity would be one of the biggest since, well, relativity.

The article refers to a device where they're using surface acoustic waves on a semiconductor to deform an optical waveguide that's constructed on the semiconductor's surface, in order to modulate the light passing through the waveguide.

If you have to visualize it directly, think of this. You've got a bedsheet that's secured along one edge to a fence. You're holding the opposite edge. This is the SAW chip surface. Stitched into the sheet is a fabric hose that's got high pressure air flowing through. That's the light waveguide.

If I shake the sheet up and down, a sheet wave ripples across the sheet, bobbling the fabric hose up and down. This squeezes the hose as the wave passes across it.

The squeezing and deformation of the fabric hose causes the air flow through the hose to change.

It's a crude analogy, but it's at least somewhat applicable.

In the actual part, the "squeezing" is a lot more complex process involving waveguide modes and non-linear processes that is a lot harder to explain. Basically, you start getting the "pipe" down to a size where the light wavelengths are significant compared to the size of the pipe, you get a lot of interactions you don't see in the normal world, but they're similar to what I have to deal with in microwave plumbing.

a reply to: yulka

Yes. I know the media article says that.
I don't know if the published paper says that.

a reply to: Bedlam

So that be simplified to, as phishy put it, variable refraction within the waveguide?
Fiber optics on a really small scale.

originally posted by: Phage
a reply to: darkorange

so that would mean that light IS affected by gravity.

That depends upon your frame of reference.

And why everyone is looking for graviton as gravity carrier force when it is just topological curvature?

Who is everyone? In any case, finding evidence for gravitons would throw a monkey wrench into general relativity which would be a big deal. Physicists like making big deals. Messing up general relavity would be one of the biggest since, well, relativity.

I think so too. thanks

a reply to: Phage



Thank you for the help...

originally posted by: Phage
a reply to: yulka

Yes. I know the media article says that.
I don't know if the published paper says that.

It does not. It's discussing a part that switches light passing through a waveguide using an electrical signal that causes deformation of the part's surface.

But that's not the sort of thing that grabs the reader's eye. It's click-bait for printed media, if you will.

a reply to: Bedlam

thank you

What are the best methods of radiation shielding for long-term manned space missions likely to be implemented in the relatively near future?
Barring of course completely counterintuitive breakthroughs. (Like for instance the discovery that just telling neutrons bombarding a ship to 'Go away', actually works...)

originally posted by: Phage
a reply to: Bedlam

So that be simplified to, as phishy put it, variable refraction within the waveguide?

It's more complex than that. The shape/size of the waveguide dictates what can pass through, if the wave and the guide are nearly the same size. Thus a small physical change to the guide can make it reflective or transmissive.

Instead of "bending light", for another analogy, it's more like light is a key, and the sound is changing the shape of the keyhole. It won't go in if the keyhole is wrong.

a reply to: Bedlam

I see.
I missed the part about being an optical switch on your first run through.

originally posted by: Phage
a reply to: Bedlam

I see.
I missed the part about being an optical switch on your first run through.

I imagine you could do a lot more than simple switching with it. Haven't got but about 15 minutes before the long night begins, though, so I won't have time to look.

Hello to all. I am kind of new here. I have not spent a lot of time reading this thread as much of it is beyond me. I do not want to interrupt the current flow of discussion so I hope it is not too rude of me to interject with my question in this way.
I just thought that this thread would have some really smart people when it comes to physics.
My question is basically this " going by the laws of physics - is it possible this crater that was left after the huge port explosion in Tianjin could be explained by an above ground chemical explosion ( the crater is over 3 acres in size and was incredibly deep before it filled with water and turned into a lake ) To me the crater looks like something penetrated there, the fractured earth around the rim, the pushing of dirt up and out from the crater. It doesn’t take a rocket scientist or a weapons development expert to come to the conclusion, based on this visual evidence alone, that this was no conventional chemical type of destruction - or at least to my limited understanding . This damage is clearly the result of a much more exotic energy release than that being reported thus so far. I don't want to get into speculation about if it was an attack or an orbital kinetic weapon or the current geoolitical climate e.t.c .e.t.c
I just want to know if the picture adds up with the official explanation of merely the equivalent to a 23tonne tnt explosion which was above ground and chemical in nature.
Anyway here is a pic of the crater
i.imgur.com...
pbs.twimg.com...:large
And I think a video to display the nature of the explosion - the size and nature of the combustion.

So once again sorry to interrupt and answer at your own leisure - I do not want to derail this thread in anyway or butt into a deep involved debate.
Thanks in advance, I am really looking forward to some smart physics minds giving their thoughts on this.

a reply to: mungbean

You aren't derailing anything. That's why the thread is called "Ask any question you want about physics".
I hadn't seen the blast crater yet, so thanks for posting those links. Very impressive.
The size of the crater would depend on a couple of different factors. One being the composition of the surface material at the blast sight. If it is a less cohesive granular soil, like a silty sand or silt clay, the force of the explosion would displace more material and further away from the epicenter than would happen on solid rock.
Another being the order in which the explosions occurred. A large primary explosion or two, as evidenced in the video, could fracture or loosen surface material, which would allow the largest of the explosions to move more of it away than had it just been the one largest explosion in an isolated event.
Another factor is exactly what was exploding. Different types of commercial explosives are manufactured for different applications. C4 (plastic explosives) react and explodes very quickly in comparison to ANFO. ANFO is a common blasting charge used in mines. It's slower detonation rate makes it better for fracturing and crumbling rock and the like. C4 is much more energetic, and is commonly used in demolition applications in the form of shape charges. In this use, the explosion superheats copper to plasma and propels it to cut through steel beams. It is also the same principle behind the RPG.

a reply to: mungbean

And unfortunately, since the exact nature of which chemicals were involved in the explosions isn't yet known, I can't really tell you much more than that. Maybe someone else here will have more insight.

a reply to: pfishy

The initial fire started from 'wood glue' according to officials. Then it was calcium carbide that created acetylene and the official version then became that it was ammonium nitrate. But does that not need a perfect ratio mixed with fuel or diesel ? I do not know.. lol which is why I am here. Now the official statement is they are still unsure of what created the blast ( and after sending a team of over 200 nuclear and chemical weapons experts to the scene after three days they still are tight lipped and can not tell us what it was )
the initial detonation after the small fire was on the eastern side of the port and whee the second giant explosion happened was the other side of the port and nowhere near the chemical storage area.
Also the ground there would have been extremely solid I would have thought. For the heavy machinery and cargo stored it definitely is not quicksand. And the other important thing to remember is the previous explosions occurred a distance away from the big one that blew this crater

a reply to: mungbean

Also, Tianjin being a port city, it is reasonably safe to assume that the native soil is going to be fairly sandy, with perhaps an overlying soft clay or silty clay layer. Though, I have not been able to find a geotechnical report from the area other than one addressing reclaimed clay slurry.
That being said, the ground is likely soft and fairly high in moisture content (probably near or even about the liquid limit, if you know what that refers to), so.it's very possible an explosion that large could have excavated the crater.
Also, what I think you were referring to as fracturing of the ground is very possibly channels carved by in flowing surface water. In soft soils, running water can cause deep erosion channels very quickly.

a reply to: mungbean

Ah, I hadn't been able to find that information.
I suppose that the wood glue must have been some sort of epoxy resin.
As far as the calcium carbide, jeez... No wonder it went up like it did. It became a huge fuel air bomb.
I don't know how much tolerance the an/fo ratio has, unfortunately. But did they say that it was created by the ongoing fire and initial explosion, or could the logistics company have been importing actual ANFO?

a reply to: pfishy

But wouldn't one of the world's biggest shipping ports. The weight of all of those shipping containers and heavy machinery would denote that the ground would have to significantly fortified ? At least if the soil was soft and near saturation point they would have to strengthen it immensely with concrete and other materials right ??? Otherwise how could all that weight be stored there ?
And the fractures surround the crater and are higher than ground level so from what I can see thee is no way any subterranean water has flowed over it.
It caused 2.9 on the ricter scale also ( the second blast )
I hope I am not sounding too ignorant here because I know I am pretty ignorant to this stuff compared to most who would frequent this thread