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[Granite26]

the actual formula isn't important, just the inputs.

The point is, the energy of light is based on the source's motion to you, just like every other kinetic particle. (train whistles or throwing a ball out of a car)

[Il Palazzo]

I'm not so sure about this, but I believe that's a consequence of dilation and not actually lack of acceleration. From your POV, you keep accelerating at the same rate, so you ARE going "faster and faster", but from the external POV you seem to be accelerating less and less. Or is it the other way around? That's why as you approach C, the people inside the ship could perceive a trip to be (near) instant, while people outside will still think you still took 4 or more years to reach the nearest star.

Ah, yes, you seem to be on the right track, as far as I can tell. There's just one more problem that I can see there. Mainly, what if you don't have any "destination point" and you just keep accelerating?
From the POV of external observer, it's rather easy to deduce: the spaceship's mass increases, it accelerates ever more slowly and it's on-board time slows down(with complete "time-stop" as the unatainable limit - asymptotic approach).
But what about POV of the space ship? As you accelerate, the universe becomes smaller in the direction of your travel(lenght contraction), but with what exactly as a limit?
And what is there to stop you from accelerating beyond said limit?

Anyway, I'll try to satisfy my failed physicist ego now, by correcting what I feel was incorrect:

Some energy has mass, yes.  But he was treating that as universally true.  Which it ain't.

It's all very blurry in my memory, but isn't it wrong? Energy has no mass per se, instead it's more correct to state that energy is a form of mass/mass is a form of energy. Or that you can associate mass to an energy quantum(and vice versa).
Maybe I got your words wrong, but are you not claiming that some forms of energy cannot be associated with mass? If so, then which ones and why(in your opinion)?

You're both kind of right. Light as a field would have no mass, but the individual photons do. Remember that light can be observed as either a particle or a wave.

1.Ok, so light is not an EM field. It's said field's oscillations.
2.And as long as you can associate energy with something, you can also associate mass to it.
3.You have to remember that changing the description mode cannot result in contradictory results e.g., light cannot gain or lose mass, just by changing description mode from wave to particle.

What happens if you calculate the red shift on an object going .99c away from you?  Current theory says you'll still measure that photon as going c, but it'll be redshift out of existance, doesn't it?

It'll just have a "very" low energy=huge wavelenght. It won't dissapear by any means.
Actually, I don't get your argument. How light's frequency being dependent on source's velocity contradicts the v=c postulate?

My knowledge is rather rusty, so feel free to tell me that I got something wrong.

[mainiac]

the actual formula isn't important, just the inputs.

The word squared is absolutely essential.  Saying it's related to velocity gives you the wrong idea.  It's related to velocity squared.

[Psyco Jelly]

Reflecting on the whole realistic space travel, it seems so complicated that it would most likely be best to just improve knowledge in other areas until an alien species that can travel space tells us how. As long as humans are the only heartless bastards in the universe, we can probably just steal alien technology.

[Servant Corps]

I do not believe reliance on an alien race in a Science-Fiction story about colonizing Solar System B would bode well. While it might be plausible, it's basically requesting for a "Deus Ex Machina" to intervene and "reveal" to us the secrets of travelling to another system. The implications are...um...not exactly good.

Though at least it's better than talking about photons.

[Virex]

I'm not so sure about this, but I believe that's a consequence of dilation and not actually lack of acceleration. From your POV, you keep accelerating at the same rate, so you ARE going "faster and faster", but from the external POV you seem to be accelerating less and less. Or is it the other way around? That's why as you approach C, the people inside the ship could perceive a trip to be (near) instant, while people outside will still think you still took 4 or more years to reach the nearest star.

Ah, yes, you seem to be on the right track, as far as I can tell. There's just one more problem that I can see there. Mainly, what if you don't have any "destination point" and you just keep accelerating?
From the POV of external observer, it's rather easy to deduce: the spaceship's mass increases, it accelerates ever more slowly and it's on-board time slows down(with complete "time-stop" as the unatainable limit - asymptotic approach).
But what about POV of the space ship? As you accelerate, the universe becomes smaller in the direction of your travel(lenght contraction), but with what exactly as a limit?
And what is there to stop you from accelerating beyond said limit?

You've also got to take time dilation into account. If I remember correctly, speed induced time dilation is symmetrical, which means that to th outside observer, the object slows down, but to the object, the outside observer slows down. So as you approach c, the world around you seems to grind to a halt.

The reason there's a limit at c in the first place has to do with the fact that if you start to appraoch c, all kinds of things happen (time dilation, space contraction, mass increase) and those things cost energy, or more precicely, a larger part of the energy is converted into those changes instead of a change in speed. The amount of energy that goes into these changes aproaches 100% of the added energy as your speed approaches c. So you will continue accelerating, but at an ever slowing pace. There's no real hard limit, you're just losing more and more of the acceleration to unwanted side-effects.

[Yanlin]

Need I remind to you people that light DOES have a mass? It's both a particle and a beam. It experiences drag. Light gets slowed down by matter. Light travels even slower underwater.

[Granite26]

What happens if you calculate the red shift on an object going .99c away from you?  Current theory says you'll still measure that photon as going c, but it'll be redshift out of existance, doesn't it?

It'll just have a "very" low energy=huge wavelenght. It won't dissapear by any means.
Actually, I don't get your argument. How light's frequency being dependent on source's velocity contradicts the v=c postulate?

You're right about the wavelength getting longer, but what about as the object (and you) increase relative speed approaching c?  What's the upper limit on the wavelength?

[mainiac]

Need I remind to you people that light DOES have a mass? It's both a particle and a beam. It experiences drag. Light gets slowed down by matter. Light travels even slower underwater.

All of which is also true of sound.  Does sound have mass?

[JoshuaFH]

Need I remind to you people that light DOES have a mass? It's both a particle and a beam. It experiences drag. Light gets slowed down by matter. Light travels even slower underwater.

All of which is also true of sound.  Does sound have mass?

Alright, I know I'm not educated enough to just butt into the more complicated parts of the debate, but that's just wrong, sound travels FASTER in water. MUCH FASTER. It travels even faster through solids than liquids.

[Il Palazzo]

Virex: I still don't get how this energy is transferred. Lorentz equations are just kinematics, not much help from them. Anyway, my physics knowledge is limited, so no big deal.

Need I remind to you people that light DOES have a mass? It's both a particle and a beam. It experiences drag. Light gets slowed down by matter. Light travels even slower underwater.

sure, it propagates slower through denser media than in vacuum, but it doesn't mean that it experiences drag - i.e. you won't stop a photon to a halt by passing it through enough water.
Light has got mass, in a way that you can calculate a mass of photon with a certain energy(E=hf; h-planck's constant, f-frequency) using the E=mc2 equation. It's got energy=it's got mass. But it does not have a rest mass.

You're right about the wavelength getting longer, but what about as the object (and you) increase relative speed approaching c?  What's the upper limit on the wavelength?

Why should there be an upper limit to the wavelenght? It's the same as not having a limit to distance, or time or when counting numbers.

[Yanlin]

Sound: It's the vibration of particles vibrating other particles around them.

Light: A particle and a beam traveling through matter. Slows down when passing matter.

In theory, it IS possible to stop a beam of light with enough matter. But there's a problem. Light is also REFLECTED. By the time you've got enough water to stop it, it all reflected outwards out of the water.

The laws of physics on light are hardly explored. But AFAIK, light does experience drag. Just very little of it. Imagine farting in space.

[Il Palazzo]

(Il Palazzo's crude school of physics)

Light: A particle and a beam traveling through matter. Slows down when passing matter.

Light(wave): an oscillation of an electromagnetic field.
Light(paricle): a quantum of electomagnetic radiation.

In theory, it IS possible to stop a beam of light with enough matter. But there's a problem. Light is also REFLECTED. By the time you've got enough water to stop it, it all reflected outwards out of the water.

If this was true, then you could detect some photons which some time ago had travelled through enough interstellar medium to slow down to a crawl.
Also, light slows down to the propagation speed characteristic of given medium right after entering it, not after it experiences enough drag. In other words, all photons in water travel at the same(lower than in vacuum) speed, and as soon as they leave water(to less dense medium) they speed up.
Although it's not really density that counts there, but IIRC, magnetic permeability.

Imagine farting in space.

I'd rather not do that. Even imagining that might be bad for my hemorrhoids.

Light might be a particle, but it doesn't have to mean that it is a particle in the sense that we commonly attach to this word. For one, unlike most atoms, electrons and other stuff, photons do not obey Pauli's exclusion principle, so you can stack infinite amount of them in one place.

[Sean Mirrsen]

Question on photons: if light indeed has an associatable "particle", wouldn't that mean that if we take an object far enough away (think individual stars in other galaxies), then it will become invisible? (or rather begin to become invisible, blinking in and out of view as fewer and fewer photons hit the observer in any given time frame; would also mean the visibility of the object you're looking at is proportional to the diameter of the outer lens of your observing device) Wouldn't that then mean it is not a wave, which would only change in intensity with distance?

(edit: alright, that one was ninja'd by Il Palazzo. Still, I find it strange. Maybe it's a particle effect that exists at the peaks of the field oscillation caused by light?)

...

Alright, let's drop the "light has mass" for the time being, let's approach from a different tangent. Sound is the vibration of the physical medium, or matter. Light (and other things) is the vibration of the other medium, the "energy" one. Which would explain the differences in behavior when being passed through various substances. It also allows to understand the reason why certain materials allow light to pass while others block it. There are the questions then about the effects observed, specifically light being subject to gravity. But since we are approaching from the different tangent, maybe it's not so much a question about light than about gravity? What if it is possible for gravity, as one of the most basic forces in the Universe, to affect the energy medium as well? Would kinda begin to explain the thing that's been bugging me - gravity exerts a force on everything around it without expending the energy of the object in any obvious way. Of course, it throws up other questions, like what happens to all the energy being absorbed, does the object gain mass from energy, etc, etc.

[Yanlin]

Hmm. Il Palazo, you are right. I did get this stuff wrong. Maybe I shouldn't post about light when I'm not in a thinking mood.

This causes me to think. Light DOES experience drag. But some force is making it go forward. If that were true, then it would manage to accelerate far more than the speed of light. Maybe the drag at that speed, even in space, cause it to not be able to accelerate any more?