Missing: one big, yellow, fiery ball

always_tyred

whyamihere wrote:

Nearly. I'm an undergrad.

Ah, well, you will never know as much about physics as you do right now.

If, however, you are a chemist, I'd seriously advise spending more time on inorganic and organic, because your physical chemistry is good enough already.

Try to explain why filtering to the ASL in a 1D box isn't possible but if you stick around long enough, you'll have spent some time there.

prj45

whyamihere wrote:

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.

As I understand it though that's not photons slowing down, it the wavefront of photons.

It's propogation is slowed as when a photon of energy is absorbed by an atom it takes a little while for a photon of energy to be emitted, but on the photonic scale there is no other speed than c.

And you can only work out where a photon will go by summing up all the possible paths it takes, so a photon that hits your eye has been everywhere in the universe, at the same time.

always_tyred

prj45 wrote:

whyamihere wrote:

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.

As I understand it though that's not photons slowing down, it the wavefront of photons.

It's propogation is slowed as when a photon of energy is absorbed by an atom it takes a little while for a photon of energy to be emitted, but on the photonic scale there is no other speed than c.

And you can only work out where a photon will go by summing up all the possible paths it takes, so a photon that hits your eye has been everywhere in the universe, at the same time.

Nah. We are all everywhere at once. Everything is. Or, rather, there is a possibility of us being anywhere at any given time. Pretty small, apart from the probability of where we seem be.

Of course, a photon, and indeed any particle, is a standing wave, and motion is a manifestation of the sum over time of the amplitude of the wave across all space.

Actually, all matter consists of standing waves.

My head hurts.

whyamihere

prj45 wrote:

whyamihere wrote:

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.

As I understand it though that's not photons slowing down, it the wavefront of photons.

It's propogation is slowed as when a photon of energy is absorbed by an atom it takes a little while for a photon of energy to be emitted, but on the photonic scale there is no other speed than c.

Pretty much, yes. The light wave slows, but the photons themselves don't. I neglected that for the sake of simplicity.

As AT says, the photon hasn't necessarily been everywhere at once, but there has been a possibility of it being anywhere at any time.

DonDaddyD

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.

Thank you.

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

What about outside the Universe or entering or travelling through a black hole?

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.

Surely that is dependant the Universe (and what we know of it) being the sum total of all that there is. Oh well until Stephen Hawking figures out gravity and its relation to the the Universe and black holes I'm keeping silent....

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.

Sounds like you are talking about a folding space (or a Warp bubble)....

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.

Spot on! +1

whyamihere

DonDaddyD wrote:

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

What about outside the Universe or entering or travelling through a black hole?

I'm sticking to single dimensions for ease. At the moment, other than string theory, all of our theories are based on the idea that there is no 'outside the universe'. As for a black hole, you can't really travel through one, unlike in sci-fi. It's just a really dense point in space that has a massive gravitational pull, and so pulls any matter or light in the vicinity in.

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.

Surely that is dependant the Universe (and what we know of it) being the sum total of all that there is. Oh well until Stephen Hawking figures out gravity and its relation to the the Universe and black holes I'm keeping silent....

It is indeed. However, until there's a legitimate theory suggesting otherwise (I wouldn't really say that string theory is fleshed out enough to be considered legitimate yet) I shall keep assuming that the universe is all there is thankyouverymuch.

whyamihere

By the way, you would probably really like Hawking's A Brief History of Time. Not an easy read, but worthwhile, as long as you appreciate that it's now getting on a bit and so there are some details which we're not all that sure about any more.

Rich158

That's it, I'm well and truly out of my depth now.

DDD - I had no idea what I was talking about either

always_tyred

Did anyone mention that light is heavy?

prj45

I did read that it can take 90,000 years for photons to escape the sun, so that's pretty slow light.

Jay dubbleU

whyamihere wrote:

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.

Sir you are geek of geeks and I salute you - I prefer time flys like an arrow - fruit flies like a banana

DonDaddyD

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.

Surely that is dependant the Universe (and what we know of it) being the sum total of all that there is. Oh well until Stephen Hawking figures out gravity and its relation to the the Universe and black holes I'm keeping silent....

It is indeed. However, until there's a legitimate theory suggesting otherwise (I wouldn't really say that string theory is fleshed out enough to be considered legitimate yet) I shall keep assuming that the universe is all there is thankyouverymuch.

Why would your mass increase exponentially as you reach c (light speed)?

OK here goes:
Isn't a black hole a point in space where gravitational fields are strong enough to move (pull) matter and light faster than its supposed infinite speed? Isn't this why light cannot escape it? We don't need to know where the light goes (though all energy is transferable - so it goes somewhere), we just know that black holes alter the movement of light. I red that a black hioles mass is theorectically infinite on the 'inside' hence its ability to pull light and lights inability to escape it....

always_tyred

Personally I think a geek is someone who knows what version of software is running on their smartphone and who uses Bing.

Being educated, but having the temerity for that education to be some non-cultural nonsense like "science" isn't geeky. Its just really difficult and you need an exceptionally large brain.

This is me at graduation, for example:

prj45

DonDaddyD wrote:

Why would your mass increase exponentially as you reach c (light speed)?

It doesn't, the force required to increase the speed of the object increases.

If you were pushing something faster and faster it would seem to get heavier and heavier to you as you required more a more energy to increase it's speed (and ultimately infinite energy to make it reach the speed of light), but it doesn't attain mass.

Time slows down though, things always move at the same "speed" through "spacetime" (slower through space faster through time, faster through space, slower through time).

And what is space, it can't be nothing right, because you can measure it?

always_tyred

prj45 wrote:

DonDaddyD wrote:

Why would your mass increase exponentially as you reach c (light speed)?

It doesn't, the force required to increase the speed of the object increases.

If you were pushing something faster and faster it would seem to get heavier and heavier to you as you required more a more energy to increase it's speed (and ultimately infinite energy to make it reach the speed of light), but it doesn't attain mass.

Time slows down though, things always move at the same "speed" through "spacetime" (slower through space faster through time, faster through space, slower through time).

And what is space, it can't be nothing right, because you can measure it?

I thought mass really did increase with speed. You have to put energy in, but as you go faster less of the energy can be manifested as speed, so it is manifested as mass.

I'm so far out of my depth its funny. Ask me a question about chemistry. Or cycling.

whyamihere

Think of black holes using the tablecloth analogy. Instead of a basketball (quite heavy, relatively produces quite a bit of bending in the fabric) have the cloth nailed to the floor (assuming that the cloth's held about chest height and that it can stretch that far) to show the massive difference in mass. Now, when you roll the marble, however fast you roll it, it's unlikely to be able to reach the other side, the curvature of the space time fabric is just too great, and it will fall in to the black hole. It doesn't speed up as far as we know, it's just that the gravitational pull is too strong for it to escape. However, this is the only time when I can see it being feasible. Light is obviously massless, and the gravitational force is so huge that it could, potentially, push the velocity above c. There is no evidence for this though. To be safe, I'll say it probably doesn't speed up, but it is theoretically feasible (and I'll make a note to look into it properly when I've had a good sleep).

Saying that a black hole is infinite inside like a greatly exaggerated version of the Tardis is a bad explanation. If anything, due to the incredibly high mass and very small radius, you can simplify it to have infinite density (it's not actually infinitely dense). The density doesn't matter a huge amount though, as gravity is defined in terms of the mass of the objects and the distance between them.

nwallace

Always Tyred wrote:

Its visiting Scotland. I don't imagine that it will be staying very long though, don't worry.

Aye been great, offsets that strong Easterly coming off the North Sea nicely the last few days, the only bad day was when that Easterly failed to arrive and it got a bit warm. I;m no built for warm weather.

cjcp

Wibble.

whyamihere

prj45 wrote:

DonDaddyD wrote:

Why would your mass increase exponentially as you reach c (light speed)?

It doesn't, the force required to increase the speed of the object increases.

If you were pushing something faster and faster it would seem to get heavier and heavier to you as you required more a more energy to increase it's speed (and ultimately infinite energy to make it reach the speed of light), but it doesn't attain mass.

Time slows down though, things always move at the same "speed" through "spacetime" (slower through space faster through time, faster through space, slower through time).

And what is space, it can't be nothing right, because you can measure it?

http://en.wikipedia.org/wiki/Mass–energy_equivalence#Conservation_of_mass_and_energy

That explains it probably better than I can, though if you need I can provide clarification. That's part of Einstein's theory of special relativity, which most of this comes from.

cjcp

whyamihere wrote:

That's part of Einstein's theory of special relativity, which most of this comes from.

I say this without having the faintest idea what the heck is going here, but I thought it was just his theory of relativity. Is there a second one?

lost_in_thought

Wow, this has been educational.

whyamihere, you are now king of scientists. DavidTQ is still king of geeks.

cjcp

One for the geeks:

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

greg66_tri_v2.0

:shock: Oh cj, do *try* to keep up!

EVERYONE knows that his theory of specal relatively was followed by his theory of general relativity.

I mean, like, deeeeerrrrr!!! :roll:

cjcp

Greg66 wrote:

specal relatively

His what? :P

greg66_tri_v2.0

whyamihere wrote:

By the way, you would probably really like Hawking's A Brief History of Time. Not an easy read, but worthwhile, as long as you appreciate that it's now getting on a bit and so there are some details which we're not all that sure about any more.

I read Brian Greene's "The Elegant Universe" a few years ago. For a few minutes I felt like I had some understanding. Then it went.

I do still remember the explanation of how the nth+1 spatial dimension can be folded into n dimensional space. That I do sort of still understand, although conceptually I found it pretty tricky to handle getting past 3 spatial dimensions though.

cjcp

Does anyone think that the Universe bends round on itself? Is the Universe flat? Does it come to end (I've seen that episode of Danger Mouse and it was pretty compelling)?

greg66_tri_v2.0

cjcp wrote:

Greg66 wrote:

specal relatively

His what? :P

Oh bollox. :oops:

whyamihere

cjcp wrote:

Does anyone think that the Universe bends round on itself? Is the Universe flat? Does it come to end (I've seen that episode of Danger Mouse and it was pretty compelling)?

Ooooh, here we go again...

There are 3 possibilities for the geometry of the universe: Closed, open and flat. In terms of the curvature of space time, the closed universe resembles a sphere, the open one resembles a horse riding saddle and the flat one is, well, flat. There has been a critical density calculated (can't remember how or what it is right now, I'll have to look it up). Essentially, this is a measure of the amount of stuff in the universe, all matter and all energy. If there's greater than the critical density, then we're in a closed universe, and eventually the universe will stop expanding and start contracting again, leading to a big crunch. If the density's lower than critical, we get an open universe, and it will never stop expanding. If the density in the universe is equal to the critical density, then we have a flat universe. In this case, the universe's expansion will slow, and stop at an infinite time (maths people: If you plotted a graph of rate of expansion on the y axis and time on the x axis, you would get an exponential curve starting high on y and low on x, moving down to being an asymptote of the x axis).

We think at the moment, and have some evidence that I may go into if anyone's really desperate, that we're in a flat universe. To add a bit more detail, gravity gets weaker the more distance is between two things, and stronger the more mass there is. A universe density equal to the critical density means that the amount of stuff and the distance between the bits of stuff are essentially balanced such that gravity can slow the expansion, but not stop it. We know roughly the amount of mass required to give the critical density, and standard matter gives about 0.04% of it. Around 30% of it is made up of dark matter (there is a theory that this is what some black holes are made of, as well as powering the Planet Express ship) and the remaining 70% is dark energy, which nobody knows a lot about...

EDIT: It kind of comes to an end. If you could fly in one direction at many times the speed of light, you would eventually reach a point where there was no matter or energy, because it hasn't had time to reach there yet, beyond which there would simply be empty space. This could be seen as the end of the universe. However, the empty space doesn't end. Unfortunately, this is something we'll probably never be able to investigate. Even if we could somehow get there, the edge has a 14 billion year headstart on us. Any transmission we send back with results would take 14 billion years to get to Earth, and I'm pretty sure there won't be any humans left in 14 billion years.

cjcp

If it's flat, did the big bang, um, explode out sideways then instead of all around, or did it release the energy 360 degrees and then the universe got stretched/flattened?

DonDaddyD

The Universe is spherical. IMO.

On Friday I'm going to demonstrate the following:

As an object moves it is not the object that increases in mass but the energy applied to moving the object.

Its possible to move faster than light.

I will also prove that speed is not a function of light or time but a function of itself measured at its base level by time then light and then against itself.

For this I will need to commute on the Kuota...