# Solar sail and c.

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Now I know it would take an infinite amount of energy and an infinite amount of time to accelerate to c but would it be possible with a solar sail that goes unimpeded and never loses sight if its star? Or would the light intensity be innsuffiecient after a point, because the way I understand it, the light from the star will always reach it (as long as it is not blocked or bent away), then the sail will always be accelerating because there would not be much of a retarding force other than gravity.

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After an infinite amount of time it would get infinitesimally close, but never actually c. That is if the star could burn for an infinite amount of time giving out an infinite amount of energy. Also negating all other particles in space.

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Not only does the intensity diminish, but as the solar sail speeds up, the source is redshifted, so the photon momentum decreases.

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I often wondered if the equations describing how much energy you need to accelerate an object had ever been interpreted differently.

such as.

Lets say acceleration stops at C. Why?

Imagine for a moment using a special gun that can shoot particles at varible speeds.

The fastest setting the gun has is C, why? cause thats the fastest speed, or the speed which light travels.

Thus You need to turn up the energy on the gun the faster you want to shoot the particle.

But if you use the fastest source there is to shoot it (light) that will be the end of acceleration relative toyou and the particle.

Now if you shoot the particle at C you will never see it leave you, because the light will be doppler shifted to a degree of zero light frequency.

And the particle will not detect the gun or anything behind it because all light will be so dramatically shifted.

If two particles are shot at eachother near C they will observer effects equal to twice their velocity. Such as that if they were both shot at C form guns at rest they would cover distance at twice C, and the light would shift between them.

Question, how far can light doppler shift for an observer in respect to the source and the obserer moving towards eachother near c?

Theoretically wouldnt two objects traveling towards eachother at 0.5 C each, experience doppler effects equal to C? And if they increased their velocity, it would not be possible to have any greater effect on doppler. Which would make one assume that light does not always travel away from its source at C if the source is moving in the direction of light.

(I understand this is not how SR explains it, but I remember I was wondering where this has been considered and shown)

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Would you not be met with a gamma ray strength frequency of electromagnetic radiation if you and another ship travled towards eachother at 0.4999 C? And would this not melt the front of your ship, let alone push you back, hold you back from accelerating?

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Theoretically wouldnt two objects traveling towards eachother at 0.5 C each, experience doppler effects equal to C?

No, the speeds do not add linearly. They would see each other as moving at 0.8c, and experience the Doppler shift of that speed. u' = (u-v)/(1-uv)

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I have always wondered about c. I remember reading about a photon being an oscillating b field and oscilating e field both producing one another and I think why is this the maximum speed? How does it display the qualities of constantcy, if all there i to a photon is this oscllating fields and how it arrives in packets called quanta or photons. How do the osclilating fields localize? Could they be explained as some kind of ripple? I mean you need a source to get the fields created and osciating in the first place. Also Isn't black body radiation also just weak light. I mean if I.R goggles can pick them up. Does this mean then anything above absolute zero would be a black body radiation emitter? When is something too "cold" to not emit black body radiation?

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Not only does the intensity diminish, but as the solar sail speeds up, the source is redshifted, so the photon momentum decreases.

Not to mention you are speeding towards other stars.

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you are considering two different theories simulatneously. the oscillating b fields and E fields that you speak of arise in maxwells equations as an explanation for light. Because light is a wave it obeys the wave equation (which can be determined independantly of the equation) after some very interesting thought experiments you will arive at an equation for the speed of light.

this equation predicts the speed of light to incredible accuracies, however it is not exactly correct and if you go down to a very small scale you will see some difference's in the speed of light from the theoretical value, which is due to quantum field theory which modifies and incorporates maxwells equations to be more accurate to the world around us and this is where the idea of a "photon" comes from.

now the reason why the speed of light is constant is because maxwell's equations provide a better description of our universe than newtonian mechanics do and they do not work with a variable speed of light. So for years scientists attempted to make maxwell's equations fit newtonian mechanics, until the best theories failed under experiment (aether), then Einstein created special relativity because it reconsiled the two theories by proclaiming maxwell's equations to be correct instead of newtonian mechanics and then proceding to modify newtonian mechanics to fit maxwell's equations and a constant speed of light. as it turns out this is the correct interpretation, and the ideas of "force", "energy", and "momentum" are incorrect and based solely on our limited human experience of life. The key to understanding relativity is that the previous notions aren't the big picture and should be modified accordingly.

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So while we are talking about light, could someone please clearify black body radiation for me. Am I wrong to assume it is electromagnetic radiation? As I see it if you heat up iron hot enough you see it glow red because the EM is now a little more intense and has a higher freequency therefore we see it glow red as opposed to it just being invisible I.R.

If this is true when is something too cold to be a black body radiation emitter?

And if nothing is too cold then is everything a source of light? Would this conclusion also mean that colour would have to exist because nothing could be in absolute darkness void of any kind of light if everything emits it?

Thanks for clarifying the E field B field question. I do see how I was getting mixed up there.

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So while we are talking about light, could someone please clearify black body radiation for me. Am I wrong to assume it is electromagnetic radiation? As I see it if you heat up iron hot enough you see it glow red because the EM is now a little more intense and has a higher freequency therefore we see it glow red as opposed to it just being invisible I.R.

If this is true when is something too cold to be a black body radiation emitter?

And if nothing is too cold then is everything a source of light? Would this conclusion also mean that colour would have to exist because nothing could be in absolute darkness void of any kind of light if everything emits it?

Thanks for clarifying the E field B field question. I do see how I was getting mixed up there.

Black body radiation is EM radiation. Even very very cold things emit it, you'd have to be at absolute zero to not emit it (which isn't going to happen). Yes, all matter is a source of EM radiation.

Not sure what you mean with colour though. Colour would have to exist? Well it exists now. But yeah, you'd always have some radiation incident on you. Even if you made a box that was totally empty of air and totally dark, the walls of the box would still be emitting radiation (probably IR) inside the box. This is one reason why getting close to absolute zero is so darned tricky, because everything is emitting radiation to one extent or another.

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Thanks. I find the idea a little strange. Everything is always emitting light. Isn't that weird?

WRT the colour I was thinking about whether something had a colour in a room void of light, I was forgetting that to produce colour you need enough energy to excite an electron to a higher orbital.

Does the EM radiation come from the heat energy something posses? Does this radiation cool the object ever so slightly as it leaves because it has to aquire the energy from somewhere?

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Everything is emitting light, but it's absorbing it, too. At thermal equilibrium, they balance. The radiation will cool the object only if it is already hotter than the surroundings. If it's colder, it will absorb more energy than it radiates.

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Everything is emitting light, but it's absorbing it, too

Infact isnt and hasnt all matter been absorbing and emmitting light for as long as the universe has been?

What I am saying is, the universe is connected like a web and has always been connected.

Even at extremely cold tempeatures there's still radiation right? low level EMR. Black body they call it?

It can be easy to think that before you turn a flash light on(as an example), it isnt emmitting energy, but infact it always has, for as long as those 'atom's have existed.

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