Large Hardon Collider

[Tristam]

Thanks to eli, tristam and woozie for the good answers, but i think i remember my question:

I got confused on something, are the frequencies we detect the ones that get reflected because the electron won't absorb the energies bouncing off it? Or are the frequencies we see the energy that gets absorbed and then re-emited because the electron goes back to the ground state? This makes it sound to me like we really see all the energy bouncing off the molecules except the energye lost due to energy conservation.

1- Is the energy that is absorded and then re-emited the one we don't see because this is the one that suffers from energy conservation?

2- the scattering explanation made it sound like all energy that bounces off a molecule is "weakened" much like in #1

3- is the energy we see the one that loses the least energy?

4- is the absorbtion and re-emision of energy only characteristic of some matter?

*to make sure my main question is clear: is the energy we see the energy that gets scattered or is it the energy that gets re-emitted? Or does this vary depending on whether the matter produces its own light or something?

edit: also thanks cyn

I'm probably not giving the best analogy, but I think the answer to your question is that it could be both. I think most of what we see in our day to day lookin' at stuff is seeing scattered light. But we could also see light that is absorbed and then re-emitted at a different wavelength. Basically, we see whatever light hits our eyes in the visible spectrum.

I really should have thought about this, but when I look at a fluorescent molecule in a microscope, a simplified explanation of what happens is I shine a laser of a single wavelength (488, for example, blue) onto my sample. I can see the scattered blue light that bounces off the sample (it actually looks like an eerie blue glow, it's really cool). Now when I look into the eyepiece, the eyepiece filters out blue light, so I no longer see the scattered light. Now I'm looking at the light that has been absorbed and then emitted by the biological sample. We can use a protein (called green fluorescent protein) that absorbs blue light, and emits green light when the excited electron relaxes back down to its original state, as Woozie described, to look at specific structures within a cell. Like, if I engineer a protein that naturally goes to a cell membrane, and tag it with green fluorescent protein, you can see the cell membrane as bright green against a soft green background in the eyepiece. Biological samples actually all autofluoresce to some extent like this if you shine enough light on them, but it's very dim, hence the need for a focused laser beam when I do experiments. It's tough to describe unless I'm actually showing someone this at the microscope.

So in one instance I'm seeing scattered light, and in another instance I'm seeing light that has been emitted by a source. My eye doesn't necessarily care about the source, just the wavelength.

Does that help?

[Kuya]

Let me see if i can pinpoint exactly what confuses me:

Woozie said:

So what if I attempt to give the electron an energy between the two states? Suppose, for example, I bombard the atom with photons who's energy is exactly half the amount required to jump from the ground state to the first excited state. Will the electron go halfway up?

Well, as I said, quantum theory wont allow this. So these photons will simply bounce off of the atom instead of being absorbed. We call this "scattering". So whatever energy these photons are, if we divide it by planks constant, we get the frequency (the color) of that light. Since this light is being scattered, we see the object as being that color.

What would happen if we shined a light at exactly the frequency we need to jump from ground to the first excited state (or some other excited state)? The photon would be absorbed. So the object would appear black.

The energy that is perceived is the energy that is bounced off, and when it is absorbed the energy is not seen.

But eli says:

So let's say light hits some object, we'll say a cloud of hydrogen in space. The incident light hits a hydrogen atom in this cloud (we'll just consider only one to make things easier), and this light imparts energy onto the atom. The atom gets excited for a brief (ie on the order of nano-seconds) time, and re-emits this light. Since energy conservation takes place, there will be some energy loss in the wavelengths that get re-emitted (since the light from a star emits electro-magnetic radiation over a vast range of frequencies). The spectrum will be missing most of the spectral lines due to energy conservation (if energy conservation didn't occur, you could potentially get an unlimited amount of energy from this process). The colors that reach your eyes are what color you see.

The energy we see is the one that gets absorbed and then re-emitted.

If i apply what eli said to woozie, then the energy that is supposed to be absorbed because it got the electron to the next state is then released again which would make is visible, but applying that, wouldn't it mean the the previously black object now produces a colour? It absorbs the energy so it is black, but then it re-emitts the energy, so now it is no longer black?

Are eli and woozie talking about two different things?

[Cyn]

In filtering light though, there are several ways of going about this. Filtering light by absorbing certain wavelengths and passing others is the quick and dirty way, but it means the medium absorbing the light absorbs the excess energy. That's why that method uses thin film called gels... it absorbs so much energy that using something durable that passes all light like glass is dangerous, it absorbs too much energy and shatters. But there is another way to do it, by deflecting the undesired wavelengths and passing the ones you want. With this method you can use a more durable medium like glass and deflect the undesired energy back into a metal frame where it can be dispersed with heat sinks and fans. These are called dichroic filters, and they are what make subtractive light mixing possible.

Edit: bit of a tangent, sorry. And what Woozie said is correct.

[Kryssan]

Why can't the biologist just post here and we can make this an all-purpose science thread? With more scientist around we could finally kick the engineers out.

I hate you too Woooooozie.

[Kuya]

I'm probably not giving the best analogy, but I think the answer to your question is that it could be both. I think most of what we see in our day to day lookin' at stuff is seeing scattered light. But we could also see light that is absorbed and then re-emitted at a different wavelength. Basically, we see whatever light hits our eyes in the visible spectrum.

I really should have thought about this, but when I look at a fluorescent molecule in a microscope, a simplified explanation of what happens is I shine a laser of a single wavelength (488, for example, blue) onto my sample. I can see the scattered blue light that bounces off the sample (it actually looks like an eerie blue glow, it's really cool). Now when I look into the eyepiece, the eyepiece filters out blue light, so I no longer see the scattered light. Now I'm looking at the light that has been absorbed and then emitted by the biological sample. We can use a protein (called green fluorescent protein) that absorbs blue light, and emits green light when the excited electron relaxes back down to its original state, as Woozie described, to look at specific structures within a cell. Like, if I engineer a protein that naturally goes to a cell membrane, and tag it with green fluorescent protein, you can see the cell membrane as bright green against a soft green background in the eyepiece. Biological samples actually all autofluoresce to some extent like this if you shine enough light on them, but it's very dim, hence the need for a focused laser beam when I do experiments. It's tough to describe unless I'm actually showing someone this at the microscope.

So in one instance I'm seeing scattered light, and in another instance I'm seeing light that has been emitted by a source. My eye doesn't necessarily care about the source, just the wavelength.

Does that help?

Yes it does actually, but reading woozie's post again, it sounds like scattering only applies to objects that don't emit light or energy on their own, and eli's explanation is for objects that emit their own light, or rather that is how i am rationalizing it. But it also makes it easier for me to understand if accept what you say and say that both occur, we see energy that is reflected, and we see energy that is re-emitted (in the same object).

[Tristam]

Let me see if i can pinpoint exactly what confuses me:

Woozie said:

The energy that is perceived is the energy that is bounced off, and when it is absorbed the energy is not seen.

But eli says:

The energy we see is the one that gets absorbed and then re-emitted.

If i apply what eli said to woozie, then the energy that is supposed to be absorbed because it got the electron to the next state is then released again which would make is visible, but applying that, wouldn't it mean the the previously black object now produces a colour? It absorbs the energy so it is black, but then it re-emitts the energy, so now it is no longer black?

Are eli and woozie talking about two different things?

I think they're talking about two different ways light can interact with matter. For most day to day purposes, we see scattered light. But we could theoretically also see light that is absorbed and then emitted by an object.

I think in most cases, absorbed light by objects here on earth is then emitted in the infrared, so we cannot see it, hence it appears black.

Woozie will probly explain it better.

[Kaylia]

I shouldn't write after taking a slee pill..but w/e..Hopefully, there wont be too much bullshit in this post.

Yes it does actually, but reading woozie's post again, it sounds like scattering only applies to objects that don't emit light or energy on their own, and eli's explanation is for objects that emit their own light, or rather that is how i am rationalizing it. But it also makes it easier for me to understand if accept what you say and say that both occur, we see energy that is reflected, and we see energy that is re-emitted (in the same object).

Everything above 0 kelvin will emit electromagnetic waves (photons), that's what we call thermal radiation. At the right temperature, it can emits wavelength in the visible domain(ie: the sun, hot metal, lava, most lamp) even if the majority of it is still emited in the infrared. That's why you notice a difference when you move between the sunlight and shadow.
http://en.wikipedia.org/wiki/Thermal_radiation.


If a photon hits an atoms, two things can happen
1) it's reflected (or scattered depending of the surface and material, but it's the same deal)
2) it's absorbed by an electron and re-emited completely, or partially (everytime an electron absorb a photon, it jumps to a higher energy level that correspond to its old state + the photon energy, but if it's unstable, it will fall back down reemitting the same photon, or two weakers photons.)




Because most objects aren't emitting in the visible, what you usually see is the reflection (scattering) of light from another source. Because white light has many wavelength in it, when you see a color, it's usually because every other wavelength (color) were absorbed. Still, it's impossible for you to distingues how the color was created since the material might have absorbed every other wavelength, it might have absorbed everything but a few color that are recombined into a new one, or it could possibly have reemited a new wavelength after absorbing another.

[Shiroikage]

I hear about amazing advances in cancer treatment, or promising cures to cancer all the time, and yet cancer is never cured. But then again, that's the same thing everyone else says about carbon nanotubes.

Do we have antibodies that can specifically recognize cancer cells? I always thought our body couldn't tell the difference.

Yeah, tumor immunology is quite complicated. There is some good evidence that our bodies recognize cancers and some antibodies/T cells can be isolated that are specific for tumor specific antigens. These antigens are usually mutated proteins in the cancers or proteins that are overexpressed in the tumor. But tumors have ways of evading the immune system as well. For example, it's been demonstrated that the generation regulatory T cells specific to tumor specific antigens are at least partially responsible for the inability of an immune system to respond to an established tumor in mice.

Another thing that limits immunotherapy for cancers in humans is that we don't have a good source for syngeneic T cells in humans. You can transfer resistance to tumors in mice by transferring T cells from one mouse to an unprimed mouse, but that is not possible in humans at this point in time.

The difficulty with treating cancer is that cancer isn't one disease. A particular cancer is not the same as someone else's cancer. If you cure one form, you can't necessarily cure another. A lot of the things that make the news and such are things that work in culture (as in this paper, obviously) or things that work in mouse or animal models. This is very problematic because these results often don't transfer to real results. We've cured cancer many times over in mice, and if you're a mouse, it's pretty safe to say that you don't have to worry about cancer. The problems are quite similar for tissue culture, but you also have the added problems associated with delivery. Drugs are metabolized when they're ingested, and you need to account for that in some way (i.e. use an activated form of the drug in culture). A big problem with this study is that, as nice as the results are, it's antibody work and a brain cancer. Antibodies don't normally cross the blood-brain barrier.

I could take for a long time about tons of different methods and possible things to investigate in the future (i.e. antibodies for tumor specific antigens with covalently linked toxins such as the ones in the paper) but it's hard to say exactly what sort of methods people are going to work on and which ones are going to show promise. Some of the stuff that people talk about isn't even remotely feasible at this time, as interesting as it may be.

And, scary as it is to think about, there is a lot of work that is not getting proper funding. One of my immunology professors has an anecdote about him meeting a rather respected tumor immunologist who was doing some interesting work (that the professor teaches about in one of the upper year immunology classes) and, shockingly, the particular immunologist quit the tumor work because he wasn't able to get proper funding.

[Max™]

Was reading an article I'm pretty sure Woozie has seen in Sci-Am a month or two back, talking more about color perception in the brain.

Figured this is a good opportunity to share these:

http://www.artelevision.com/images/t...ble_Colors.jpg
http://t0.gstatic.com/images?q=tbn:7...-Yelue.svg.png

You gotta cross your eyes to see them properly, then relax and let the colors fight it out.

Reddish Green, and Yellowish Blue are not colors we are really able to see, neat!

More stuff on the related ideas here: http://www.reddit.com/r/todayilearne..._perceive_two/

[Lhyet]

I've been going through the manifestos for the three main parties in the upcoming UK general election, and the Liberal Democrats (who have little chance of winning anyway) say they would reject a new generation of nuclear power plants if they won.
After reading so many of Kryssan's posts on this matter, I would find it even more difficult to vote for this already weak party.

It's amazing that they want nothing to do with nuclear power and wish to make the UK 100% dependant on renewable energy sources by 2050. The country would become airborne with that number of wind turbines.
Their own ignorance, or politicians just trying to claw as many votes from the media led uninformed people as possible?

[Chun Liroy]

Goddamn it I need to read the instructions for the paper before I get halfway through them. Doing a paper on viral vectors in gene therapy (shiro knows ) and I didn't realize that the structure of the paper had to be Abstract>intro>discussion>conclusions thought it was a normal paper not a lab report-esque version. "You should be able to address your topic in relation to things that are important in society today." Well now I definitely can't get as technical as I want to. Also found out it's due tomorrow night by 11:59 and I thought it was do 10Am tomorrow. I shall finish it tonight though!

[Woozie]

I freaking hate lab reports. I hate papers too, but I hate lab reports even more, mainly because me typing a lab report usually implies I had to do some experiment (which I really hate).

[Chun Liroy]

I love writing lab reports when the results of the lab really need to be interpreted and not the normal "this makes sense because we know that xxx happens," if that makes sense to you at all. AKA actualy labs and not prepped labs used as teaching tools. Such as the electrophoresis and E. Coli lab that we're doing now that i've done in high school before. -.- Sometimes if I don't think about what I'm saying for like 5 minutes I don't make sense half the time.

[Kaylia]

I freaking hate lab reports. I hate papers too, but I hate lab reports even more, mainly because me typing a lab report usually implies I had to do some experiment (which I really hate).

Worst part about lab reports is when you have to report a failled experiment...which is pretty damn common. You have to fill it with

[Chun Liroy]

I find failed experiments are the more entertaining to write because you get to explore all the different reasons why it failed rather than focus on "this is why it works." Again from an academic point of view more-so than a job-based perspective.

[Kuya]

I shouldn't write after taking a slee pill..but w/e..Hopefully, there wont be too much bullshit in this post.




Everything above 0 kelvin will emit electromagnetic waves (photons), that's what we call thermal radiation. At the right temperature, it can emits wavelength in the visible domain(ie: the sun, hot metal, lava, most lamp) even if the majority of it is still emited in the infrared. That's why you notice a difference when you move between the sunlight and shadow.
http://en.wikipedia.org/wiki/Thermal_radiation.


If a photon hits an atoms, two things can happen
1) it's reflected (or scattered depending of the surface and material, but it's the same deal)
2) it's absorbed by an electron and re-emited completely, or partially (everytime an electron absorb a photon, it jumps to a higher energy level that correspond to its old state + the photon energy, but if it's unstable, it will fall back down reemitting the same photon, or two weakers photons.)




Because most objects aren't emitting in the visible, what you usually see is the reflection (scattering) of light from another source. Because white light has many wavelength in it, when you see a color, it's usually because every other wavelength (color) were absorbed. Still, it's impossible for you to distingues how the color was created since the material might have absorbed every other wavelength, it might have absorbed everything but a few color that are recombined into a new one, or it could possibly have reemited a new wavelength after absorbing another.

This clarifies all of it. Thanks !

[Kaylia]

I find failed experiments are the more entertaining to write because you get to explore all the different reasons why it failed rather than focus on "this is why it works." Again from an academic point of view more-so than a job-based perspective.

3-4 years ago, I would have agreed, but when you make more serious experiments, it's not that fun. Not only do you waste 10 times more time on an experiment that isnt working, because well...you don't give up after the first faillure (I spent over 50h at school in a week on something that could have taken 10h a few times), but lab reports are also much longer to write. Sometime you have no fucking clue why it did not works because the equipment is broken, and you can't tell easily.

[Shiroikage]

All of my third year labs had extremely indepth lab reports. Always lots of references for them. Was a bit of a pain.

And now that the only experiments I do are actual work, failure is a bit frustrating if you can't find the cause. It means that you don't have anything to show, you don't really know why you don't have anything to show, and you certainly don't have anything that can be published. Thankfully, I haven't had any rough stretches that lasted more than a couple of weeks.

[Quicklet]

I don't think this has been posted yet. Needless to say, it's... amazing.

http://www.youtube.com/watch?v=oaG6umMkbxg

Also, there's a new calculation out that claims to have the strange quark mass to within 1.5% error (down from the previous calculation's 30%). Should be interesting to see whether or not it's supported by evidence in the future.

[Eliseos]

Holy crap, I wish I was an hour late from class and I would have seen this:

(CNN) -- Authorities in several Midwestern states were flooded Wednesday night with reports of a gigantic fireball lighting up the sky, the National Weather Service said.
The fireball was visible for about 15 minutes beginning about 10 p.m., said the National Weather Service in Sullivan, Wisconsin, just west of Milwaukee.
"The fireball was seen over the northern sky, moving from west to east," said the NWS in the Quad Cities area, which includes parts of Iowa and Illinois.
"Well before it reached the horizon, it broke up into smaller pieces and was lost from sight," the service said. "Several reports of a prolonged sonic boom were received from areas north of Highway 20, along with shaking of homes, trees and various other objects including wind chimes," it said.
It said the fireball was seen across parts of Missouri, Illinois, Indiana and Wisconsin. CNN affiliate WISN-TV said that people in Ohio also saw it.
Video from WISN showed a massive ball of light exploding across the sky. The Doppler Radar from the Quad Cities weather service appeared to capture a portion of the smoke trail from the fireball at just after 10 p.m., the NWS said. It appears as a thin line extending across portions of Grant and Iowa Counties in Wisconsin.
There has been no official determination as to what caused the fireball, the NWS in Sullivan said.
However, it said there is a meteor shower called Gamma Virginids that occurs from April 4 to April 21, with peak activity expected on Wednesday and Thursday.
"A large meteorite could have caused the brilliant fireball that has been reported," the National Weather Service said.
The NWS in Quad Cities said that it was unknown if any part of a meteorite hit the ground.
According to NASA, a meteor appears when a meteoroid -- a particle, chunk of metal or stony matter -- enters the Earth's atmosphere from outer space.
"Air friction heats the meteoroid so that it glows and creates a shining trail of gases and melted meteoroid particles," it said. "People sometimes call the brightest meteors fireballs."

http://www.cnn.com/2010/TECH/04/15/m...ion=cnn_latest