Missing: one big, yellow, fiery ball

jonginge

DonDaddyD wrote:

If all types of light travel at a single constant speed, it would only have a singular form.

However, light acts as both particles and waves. It travels faster in one form than the other. That is why it is able to do so.

Get you to CERN! You could sort out the theory of everything: pBrains to the lot of them

cee

Blue skies in sunny edinburgh! course its forecast to persist down tomorrow.

Kieran_Burns

For those that aren't sure - think refraction....

Or rainbows....

http://en.wikipedia.org/wiki/Refraction

cee

the speed of light also varies depending on the medium through which it (light) travels...and space is not entirely empty

OldSkoolKona

cjcp wrote:

I distinctly remember putting sun cream on this morning before I left the house.

I think there you have your answer as to why the sun has gone away..

itboffin

Guess which day I decided not to bring a jacket or long sleeve jersey nor my leg warmers or my b**** overshoes :evil:

jonginge

cee wrote:

the speed of light also varies depending on the medium through which it (light) travels...and space is not entirely empty

*mumble, mumble, magnetic permeability, electric permittivity, mumble, mumble*

*mumble, mumble, Cerenkov radiation, mumble, mumble*

lost_in_thought

itboffin wrote:

Guess which day I decided not to bring a jacket or long sleeve jersey nor my leg warmers or my b**** overshoes :evil:

MTFU!

It's neither raining nor actually cold.

FFS.

Kieran_Burns

itboffin wrote:

Guess which day I decided not to bring a jacket or long sleeve jersey nor my leg warmers or my b**** overshoes :evil:

Excuse me?

When did you become ghey?


I might have to hit the report button on your post for exceeding the ghey limits of this forum

itboffin

Ask Attica & Linsen I do not like the cold yesterday was just warm enough for me not to wear leg warmers and only then in the evening in the morning I was bloody freezing, damn those colour coordinated fingerless gloves.

itboffin

lost_in_thought wrote:

itboffin wrote:

Guess which day I decided not to bring a jacket or long sleeve jersey nor my leg warmers or my b**** overshoes :evil:

MTFU!

It's neither raining nor actually cold.

FFS.

Erm no ones listening to you, you make us stand outside the Morpeth until it's almost snowing and even then you don't even wear shoes with toes :P

linsen

Boffin - get some more padding on you ;-)

It is now officially shorts weather and will be till Christmas Day or thereabouts (according to my son, anyway)

Rich158

DonDaddyD wrote:

If all types of light travel at a single constant speed, it would only have a singular form.

However, light acts as both particles and waves. It travels faster in one form than the other. That is why it is able to do so.

Edit: To add; Waves travel at different speeds (think Sound waves, which can be slow or fast). Light in the form of waves are no exception to the rule.

You are making the assumption that light is actually a wave. iirc correctly it isn't but when subjected to the right conditions it can be made to act like a wave, the same is true for making it act like a particle, hence the theory of wave particle duality put forward by Einstein in the early 1900's. Light is in fact a form of electromagnetic radiation, and travels in pockets of energy called photons.

And also light travels a pretty much a constant speed in any medium, it is the time lost between entering and exiting a medium that appears to make it speed up or slow down.

How about that for geeky and pedantic

always_tyred

DonDaddyD wrote:

If all types of light travel at a single constant speed, it would only have a singular form.

However, light acts as both particles and waves. It travels faster in one form than the other. That is why it is able to do so.

Edit: To add; Waves travel at different speeds (think Sound waves, which can be slow or fast). Light in the form of waves are no exception to the rule.

Sorry to disappoint you DDD, but only get thee to CERN is they've asked you to provide lunchtime entertainment.

Light can be observed to behave as a wave, or as a particle, depending on what you want to see. But it is what it is.

cee

Rich158 wrote:

And also light travels a pretty much a constant speed in any medium,
How about that for geeky and pedantic

surely a pedantic geek would never say pretty much constant..

jonginge

I refer you to my mumble of 45 mins ago

DonDaddyD

@Rich and Always Tyred,

You do realise that I have absolutely no idea what I'm talking about , I hated Physics and I think I'm using a combination of Comic, StarGate and Star Trek (mostly StarGate) knowledge against you.

That said:

it is the time lost between entering and exiting a medium that appears to make it speed up or slow down.

Isn't the displacement of time * distance travel = speed?

What I'm saying is that speed is measured by time taken to travel a certain distance.
If two beams of light are measured from one end of the table to the other, and a medium is placed between one beam of light making that beam of light take longer to get to the end of the table then isn't that beam of light traveling slower (having taken longer) than the other beam of light (that was unhinered by said medium).

Light can be observed to behave as a wave, or as a particle, depending on what you want to see. But it is what it is.

But whilst it is behaving as a wave it is subject to travel as a wave travels. Waves travel at different speeds e.g. like sound waves.

cjcp

Ok, come on, own up: how many of you geeks actually tried to make Kelly Le Brock using a kettle, a BBC B and a remote control*? Come on. :P

*For which, I don't blame you one bit.

Porgy

dilemna wrote:

Still we are promised lots of rain for the w/e in south and east.

Everytime I plan a cycle trip this happens - I was going to cycle to Margate and back over two days. Bugger.

Last time I planned a trip was a couple of weeks ago when we got that storm, and all that wind

always_tyred

Rich158 wrote:

DonDaddyD wrote:

If all types of light travel at a single constant speed, it would only have a singular form.

However, light acts as both particles and waves. It travels faster in one form than the other. That is why it is able to do so.

Edit: To add; Waves travel at different speeds (think Sound waves, which can be slow or fast). Light in the form of waves are no exception to the rule.

You are making the assumption that light is actually a wave. iirc correctly it isn't but when subjected to the right conditions it can be made to act like a wave, the same is true for making it act like a particle, hence the theory of wave particle duality put forward by Einstein in the early 1900's. Light is in fact a form of electromagnetic radiation, and travels in pockets of energy called photons.

And also light travels a pretty much a constant speed in any medium, it is the time lost between entering and exiting a medium that appears to make it speed up or slow down.

How about that for geeky and pedantic

That's wrong.

What you are describing is the fact that the great majority of matter is free space. But is possible to define what is matter and what isn't and to thereby define a medium (of matter) and a vacuum. Light travels more slowly due to interaction with matter. If you wish to use particle-like terminology, this results from both elastic and inelastic collisions.

Light and electromagnetic radiation are interchangeable terms.

Wave particle duality isn't a theory describing some actual change, its a description of the observation that light, which is always light, behaves as both, depending on how you interrogate it (which is largely a question of the scale of the measured phenomenon).

Hopefully that's sufficiently pedantic.

Jay dubbleU

DonDaddyD wrote:

If all types of light travel at a single constant speed, it would only have a singular form.

However, light acts as both particles and waves. It travels faster in one form than the other. That is why it is able to do so.

Edit: To add; Waves travel at different speeds (think Sound waves, which can be slow or fast). Light in the form of waves are no exception to the rule.

Actually (uber uber geek) it is the frequency of light waves that changes their colour - the speed of light in either particle or wave form is a constant - hence the red shift effect - stars moving away appear blue - those moving towards us appear red - translated into sound as the Doppler effect

benno68

Sewinman wrote:

It is in my pants. I have harnessed its power.

Great balls of fire!!! Not sure about the "great" bit of it but we'll leave that subject alone.

Looks like it may have popped out of your pants as we're still enjoying the sun in Cardiff.

greg66_tri_v2.0

Always Tyred wrote:

Rich158 wrote:

DonDaddyD wrote:

If all types of light travel at a single constant speed, it would only have a singular form.

However, light acts as both particles and waves. It travels faster in one form than the other. That is why it is able to do so.

Edit: To add; Waves travel at different speeds (think Sound waves, which can be slow or fast). Light in the form of waves are no exception to the rule.

You are making the assumption that light is actually a wave. iirc correctly it isn't but when subjected to the right conditions it can be made to act like a wave, the same is true for making it act like a particle, hence the theory of wave particle duality put forward by Einstein in the early 1900's. Light is in fact a form of electromagnetic radiation, and travels in pockets of energy called photons.

And also light travels a pretty much a constant speed in any medium, it is the time lost between entering and exiting a medium that appears to make it speed up or slow down.

How about that for geeky and pedantic

That's wrong.

What you are describing is the fact that the great majority of matter is free space. But is possible to define what is matter and what isn't and to thereby define a medium (of matter) and a vacuum. Light travels more slowly due to interaction with matter. If you wish to use particle-like terminology, this results from both elastic and inelastic collisions.

Light and electromagnetic radiation are interchangeable terms.

Wave particle duality isn't a theory describing some actual change, its a description of the observation that light, which is always light, behaves as both, depending on how you interrogate it (which is largely a question of the scale of the measured phenomenon).

Hopefully that's sufficiently pedantic.

Ooh, ooh, ohh. Nerd fight! Nerd fight!

Watch out for those ball point pens in the top pocket of your labs coats boys.

And no slapping with your clipboards.

prj45

cee wrote:

the speed of light also varies depending on the medium through which it (light) travels...and space is not entirely empty

Photons always travel at the speed of light though.

whyamihere

Enter the physics geek...

Why the sun appears yellow:
Its surface temperature is around 2500K (Kelvin). Photons emitted by a surface of this temperature appear yellow in colour. Observe: http://en.wikipedia.org/wiki/Black_body ... d_its_star

However, there is some change in the colour due to atmospheric refraction.

Light stuff:
In a vacuum, light travels at a constant speed called c, 3x10^8ms^-1 (300 million metres per second). This only applies to a vacuum. Through air, light will generally travel very close to c, but in other materials is travels much slower. If a sample of glass had, for example, a refractive index of 1.5 (a vacuum's refractive index is 1), then light in the glass would travel at 2x10^8ms^-1, as v/c = n1/n2 (c=speed of light, v=speed of light in glass, n1=refractive index of vacuum, n2=refractive index of glass). The light actually moves more slowly. Imagine pushing a boat through water, and then through treacle. The treacle would have a higher 'refractive index', and for the same applied force, will travel more slowly.

DDD mentioned the wave/particle duality, but appears slightly confused about what it means. The 'particles' are virtual, they don't really exist in the traditional sense of particles. They have no mass, and so are required by relativity to move at the speed of light. The wave particle duality idea comes from the fact that light appears to act as a wave or a particle depending on the situation. In Young's double slit experiment, for example, light is clearly acting in a wave like manner. The photoelectric effect, however, requires light to act as a particle. This has nothing to do with the speed of the light.

I fully expect this to be ignored due to my use of numbers.

DonDaddyD

Jay dubbleU wrote:

DonDaddyD wrote:

If all types of light travel at a single constant speed, it would only have a singular form.

However, light acts as both particles and waves. It travels faster in one form than the other. That is why it is able to do so.

Edit: To add; Waves travel at different speeds (think Sound waves, which can be slow or fast). Light in the form of waves are no exception to the rule.

Actually (uber uber geek) it is the frequency of light waves that changes their colour - the speed of light in either particle or wave form is a constant - hence the red shift effect - stars moving away appear blue - those moving towards us appear red - translated into sound as the Doppler effect

There's a comic character - Galactus Herald specifically called Redshift

DonDaddyD

whyamihere wrote:

Enter the physics geek...

Why the sun appears yellow:
Its surface temperature is around 2500K (Kelvin). Photons emitted by a surface of this temperature appear yellow in colour. Observe: http://en.wikipedia.org/wiki/Black_body ... d_its_star

However, there is some change in the colour due to atmospheric refraction.

Light stuff:
In a vacuum, light travels at a constant speed called c, 3x10^8ms^-1 (300 million metres per second). This only applies to a vacuum. Through air, light will generally travel very close to c, but in other materials is travels much slower. If a sample of glass had, for example, a refractive index of 1.5 (a vacuum's refractive index is 1), then light in the glass would travel at 2x10^8ms^-1, as v/c = n1/n2 (c=speed of light, v=speed of light in glass, n1=refractive index of vacuum, n2=refractive index of glass). The light actually moves more slowly. Imagine pushing a boat through water, and then through treacle. The treacle would have a higher 'refractive index', and for the same applied force, will travel more slowly.

DDD mentioned the wave/particle duality, but appears slightly confused about what it means. The 'particles' are virtual, they don't really exist in the traditional sense of particles. They have no mass, and so are required by relativity to move at the speed of light. The wave particle duality idea comes from the fact that light appears to act as a wave or a particle depending on the situation. In Young's double slit experiment, for example, light is clearly acting in a wave like manner. The photoelectric effect, however, requires light to act as a particle. This has nothing to do with the speed of the light.

I fully expect this to be ignored due to my use of numbers.

+1 I fully admit that I have no idea what I was talking about but I have an idea of what you are talking about.... I'm surprised and wierdly warmed by all the responses.

(I believe I read the numbers before in an argument about the Flash and the Speed Force - which is faster than light and whether Superman Prime, who can escape the Speed Force, could fly faster than light - What couldn't be explained is how the Flash's mass/weight doesn't increase the faster he goes).

Questions,

So to clarify, the speed that light travels can be slowed?

I take it its harder to make light travel faster becuase the passage of light is generally beyond our perceptions?

If you are travelling faster than light, does that mean your travelling faster than time i.e. time travel?

What's hard light?

What is folding space?

whyamihere

DonDaddyD wrote:

Questions,

1. So to clarify, the speed that light travels can be slowed?

2. I take it its harder to make light travel faster becuase the passage of light is generally beyond our perceptions?

3. If you are travelling faster than light, does that mean your travelling faster than time i.e. time travel?

4. What's hard light?

5. What is folding space?

Numbered for clarity.

1. Yes, if it enters a denser medium than a vacuum (ie, anything). Scientists have actually caused light to stop, using a supercooled glass, near absolute zero.

2. You can't make light travel faster than c, 3x10^8ms^-1. That's the limit.

3. You can't. c is the limit, defined by relativity. As you approach c, your mass will increase exponentially. As F=ma, that means that in order to keep accelerating, you will need an exponentially greater force pushing you. The only way you can ever hit c is with an infinitely large force, which obviously means you can't travel any faster.

What can (theoretically) be done is to create a wormhole between two areas of space time, which create a shortcut. I'll go into more detail in 5.

4. Hard light is the opposite of soft light. Light's softness a term used to describe the way it forms shadows. If you hold your finger in front of a torch, as you move the torch away, the edges of the shadow cast by your finger will become harder, more defined. The size of the light source also affects this. It's not so much a property of light, as an effect of circumstance.

5. The interesting one. Einstein's model of the universe from which the equations of relativity are derived is best described in an analogy. Imagine a tablecloth pulled taught between two people holding it. If you roll a marble across it, the marble will move in a straight line. This represents light moving in empty space.

If you place a basketball in the middle of the cloth, the cloth will sink around it due to the weight of the ball. If you now roll the marble, it will spiral in towards the ball. If you roll it fast enough, its will only bend a little. This is what happens with gravity. Gravity is essentially a bending of the 'fabric' of space time, and it causes light to be bent. around planets and stars for example. This effect has been observed experimentally. It technically happens around anything with mass, but the effect is only large enough to be observed around very heavy objects such as stars and planets.

If we consider space time as a fabric, then we can also envisage folds and ripples (though none have been found). These folds and ripples are what make the wormholes I mentioned earlier possible. If you imagine them as a range of mountains, then the light has to travel over the peaks and through the valleys. If we cut a tunnel straight under the mountains (the wormhole), then even if we're not moving as quickly as the light, we can get to the other side more quickly by virtue of travelling a shorter distance.

Time travel is something of a possibility, if you move away from the science fiction idea of it. The faster you move, the slower time flows for you. If you're on a plane which is flying at 500mph, you're ageing fractionally slower than if you were on the ground. So, if you flew away from earth at something like (all numbers made up) 99% c, flew for 5 years, then returned at the same rate, your body will have aged 10 years, but everyone on Earth will have aged (for example) 50 years. Therefore, you have travelled into the future. You can't ever go back though. Look up the twins paradox for more on this.

always_tyred

You are one of those sad, lonely postdocs who puts all the useful stuff on Wikipedia that I employ in my job to create the veneer of knowing what I'm talking about, aren't you?

Thanks. Really.

whyamihere

Nearly. I'm a sad lonely undergrad.