Questions about light

shinbits said:

One thing I've from Kent Hovind is that the speed of light increases relative to where the light is coming from. For example, light from the headlights of a car would travel at the speed of light plus whatever speed the car is moving at.

I know this is wrong. My question is, why?

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Sorry, can´t answer that. It does. That´s strange and counter-intuitive for humans, but it does.

Secondly, when something is moving fast in front of you, it appears blurry.

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That effect is not based on physics or the attributes of light. The scale is much to small for relativistic effects to come into play here. Rather, it is based on the hard- and software of the observer: the human eye and mind.

So given the speed of the earth's rotation, especially at the equator, why don't things appear blurry?

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You have answered it for yourself in your first sentence here: "... when something is moving fast in front of you..."
As you, the observer, being stationary on the earth, move at the same speed, nothing moves "in front of you". The movement would have to be fast in relation to the observer to be noticed.

If an astronaut started spinning in Zero G, things would look blurry to him/her.

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I cannot follow you here: is there any relevance to the Zero G?

Any help on these questions is appreciated.

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Hope that helped a little.

shinbits said:

One thing I've from Kent Hovind is that the speed of light increases relative to where the light is coming from. For example, light from the headlights of a car would travel at the speed of light plus whatever speed the car is moving at.

I know this is wrong. My question is, why?

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Not sure. I think it has something to do with the way light propagates through space.

Maybe the 'Light speed' episode of The Universe can help you. I watched it quite some time ago so not completely sure if they tackle the reason. But I'm guessing it does. Lemme know will ya

http://www.youtube.com/watch?v=8BcTHmXTMyY
(Other 4 parts also on youtube)

Secondly, when something is moving fast in front of you, it appears blurry. So given the speed of the earth's rotation, especially at the equator, why don't things appear blurry? If an astronaut started spinning in Zero G, things would look blurry to him/her.

Any help on these questions is appreciated.

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I think it has to do with the amount of degree you 'spin', ie: the distance between point A and B in a short amount of time so that your eyes can't register the transition. Our earth rotates aprox 15 degrees every hour which is only 0.0042 degrees every second.

Imagine a car moving 100 kph right in front of you and then the same car 100 kph at a distance of 500 meter. the angle at which each meter the car travels is much less, thus the distance your eyes need to adjust each milisecond to stay in focus is also much less.

Maybe there's another explanation as well but I think your eyes simply not being able to adjust and respond quick enough is the biggest influence.
The way your brain processes the gaps of information probably also has something to do with it. (Kinda like when you blink you don't really notice it)

Distance does matter and if the astronaut in your example was rotating at the same amount of degree the earth does I don't think he would see everything blurry.
Set your camera to a shutter speed of around 10-20 seconds and you will see the blur (movement of stars) on camera though.

- Ectezus

shinbits said:

One thing I've from Kent Hovind is that the speed of light increases relative to where the light is coming from. For example, light from the headlights of a car would travel at the speed of light plus whatever speed the car is moving at.

I know this is wrong. My question is, why?

Click to expand...

I think it has to do with the particle/wave duality. A sound wave produced by the same car will travel at the speed of sound regardless of how fast the car is going the only major effect on the wave by the speed of its source will be the doppler effect. The same is true about the light.

shinbits said:

nah, the video doesn't tackle the reason. still interesting tho.

this brought up some more questions though.

the vid mentioned how it would take 8 min (approximately) to know that the sun wasn't there, if it vanished. so does that mean that heat travels at the same speed as light? what I'm saying is, that heat energy should still remain, even after the earth gets dark, shouldn't it?



thanx.

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The process by which heat travels in space is called radiation- in this process heat radiations travel without any medium. heat radiations are actually infra red radiations which are a part of the electromagnetic spectrum....... hence they travel with the speed of light. There are other methods of heat transfer like conduction( requires medium but there is no bodily movement of medium particles like in the case of transfer of heat through metals) and convection( requires medium but in this case medium particles are transferred along with the heat)

shinbits said:

the vid mentioned how it would take 8 min (approximately) to know that the sun wasn't there, if it vanished. so does that mean that heat travels at the same speed as light? what I'm saying is, that heat energy should still remain, even after the earth gets dark, shouldn't it?

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There are multiple ways for heat to transfer. The one we experience the most is conduction and convection.
The 3rd way is heat through radiation which travels at the speed of light (photons)

So if the sun were to magically vanish we would not know about it 8 minutes later. But also loss of heat and even gravity would arrive at a 8 minute delay. I'm guessing even a change in Earth's magnetic field because of no more solar wind to 'push it back'.

Edit: Tanzanos beat me to it

- Ectezus

Ectezus said:

Edit: Tanzanos beat me to it

- Ectezus

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LOL! Dank je well

shinbits said:

One thing I've from Kent Hovind is that the speed of light increases relative to where the light is coming from. For example, light from the headlights of a car would travel at the speed of light plus whatever speed the car is moving at.

I know this is wrong. My question is, why?

Click to expand...

it's transfer of energy in relativity.
when you sit in a train, and it comes to a sudden stop, don't you feel you are throw forward still? If you are walking in the train, you put forth Pe1(Potential energy) to walk, and the train also put forth Pe2, and when the train sudden stopped, your force is Pe1+pe2. Hence light travel is also the same increase.

shinbits said:

Secondly, when something is moving fast in front of you, it appears blurry. So given the speed of the earth's rotation, especially at the equator, why don't things appear blurry? If an astronaut started spinning in Zero G, things would look blurry to him/her.

Any help on these questions is appreciated.

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it's also relativity, though the speed traveling by equator is not as fast as you think. when you rotate your head at a fix angle X to look from A to B. you can either look at something far, for something close. The close one has shorter distance between the 2, while the far one has a longer distance. hence even though you rotate at a fix rate and the same angle, the speed of things you see are at different rate of travel depend on their distance to yours. so things at far looks bury while things close by are not. But even at equator, it's not that fast.

shinbits said:

One thing I've from Kent Hovind is that the speed of light increases relative to where the light is coming from. For example, light from the headlights of a car would travel at the speed of light plus whatever speed the car is moving at.

I know this is wrong. My question is, why?

Click to expand...

The theory of special relativity is causing this. Basically, as something approaches the speed of light, the movement of that object through time slows down (consider it a transferal of energy from movement to time to movement through space). At lower speeds this effect is virtually unnoticeable but it increases exponentially and because of the sheer speed of light this miniscule effect is enough so that any observer, regardless of relativistic speed between the two observers, will see the photon moving at 1c in a vacuum. This effect is called time dilation.

shinbits said:

One thing I've from Kent Hovind is that the speed of light increases relative to where the light is coming from. For example, light from the headlights of a car would travel at the speed of light plus whatever speed the car is moving at.

I know this is wrong. My question is, why?

Click to expand...

The slam dunk answer is because the speed of light comming from a car or a stationary flashlight or a far away star have all been measured and it is the same.

All else is explaining the observed data. But the data trumps all.

buzzini said:

it's transfer of energy in relativity.
when you sit in a train, and it comes to a sudden stop, don't you feel you are throw forward still? If you are walking in the train, you put forth Pe1(Potential energy) to walk, and the train also put forth Pe2, and when the train sudden stopped, your force is Pe1+pe2. Hence light travel is also the same increase.

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The point of special relativity is that this doesn't happen: no matter how fast the source is moving, the light it emits will always travel at c.
This quality of the universe is one of Einstein's biggest achievements.

shinbits said:

One thing I've from Kent Hovind is that the speed of light increases relative to where the light is coming from. For example, light from the headlights of a car would travel at the speed of light plus whatever speed the car is moving at.

I know this is wrong. My question is, why?

Click to expand...

The special theory of relativity states that the speed of light is the same in every reference frame. This statement is not ad hoc, and follows directly from the classical theory of electrodynamics (i.e. it's based on the way electric charges and current-carrying electrical wires work). The light from the headlights on a car would appear to the driver as if they are moving away at the speed of light. The light would also appear to be movig at the speed of light from the perspective of a stationary observer who is standing in the car's path (and hopefully he'll use this information to get out of the way). This is a rather counterintuitive statement, since a baseball or other object thrown by the driver at the stationary observer would appear to travel at the thrown speed plus the speed of the car. It turns out that this effect is just a low-velocity limit of a more general form of classical mechanics. At speeds greater than about half the speed of light, relativistic effects become important. Fast moving objects appear to be contracted in the direction of motion, to experience time more slowly, and to increase in mass. It sounds complicated (and it is, seeing as how I don't know any grad students in my department who've successfully done the relativity problem on the PhD qualifier!), but special relativity can actually be described by a very elegant formalism.

shinbits said:

Secondly, when something is moving fast in front of you, it appears blurry. So given the speed of the earth's rotation, especially at the equator, why don't things appear blurry? If an astronaut started spinning in Zero G, things would look blurry to him/her.

Any help on these questions is appreciated.

Click to expand...

That's more of an effect of the way your mind works. The moon moves at a rather high speed relative to the earth, and it can be seen very clearly. The Hubble Space Telescope sees clear images of galaxies that are moving at about 9/10 the speed of light. There's no physical blurring effect from high speeds. But there is an effect called the relativistic Doppler shift. Objects moving toward you will appear to have an increased frequency of light (blue shifting), and objects moving away will have a decreased frequency (red shifting).

Silent Bob said:

I think it has to do with the particle/wave duality. A sound wave produced by the same car will travel at the speed of sound regardless of how fast the car is going the only major effect on the wave by the speed of its source will be the doppler effect. The same is true about the light.

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Actually this is not entirely correct, and there are two problems I should address here. First, the wave/particle duality is not an important effect here. The theory of light is almost a purely classical theory. The quantization of light is only important for a few physical effects like the photoelectric effect, though this does provide the motivation for quantum mechanics. Secondly, your description of the wave velocity and the Doppler shift is correct, but remember also that light does not travel in a medium. The idea of a medium of propagation for light is known as the ether theory, and the existence of the ether was disproven by the Michelson-Morley experiment which yielded a null result. The theory was rendered meaningless by the contribution by Einstein of Special Relativity. In fact, the constancy of the speed of light in all reference frames is what necessitates Special Relativity.

Secondly, when something is moving fast in front of you, it appears blurry. So given the speed of the earth's rotation, especially at the equator, why don't things appear blurry? If an astronaut started spinning in Zero G, things would look blurry to him/her.

Click to expand...

this has nothing to do with relativity or light and everything to do with the perception of your eyes...

when you see something, all you see is a blended image of whatever appeared in front of you for the last quarter second, about. People only perceive the world in frames of about 1/4 seconds... any light that hit your eye in that last 1/4 second was blended together in your brain to form what you see now.

so if something is moving fast relative to you it will appear blurry because it was covering a lot of ground in that 1/4 of a second. But since you're spinning just as fast as the earth is... if something is stationary relative to you it won't appear blurry, even if both you and the object are moving very fast, as long as you're moving fast together.

shinbits said:

One thing I've from Kent Hovind is that the speed of light increases relative to where the light is coming from. For example, light from the headlights of a car would travel at the speed of light plus whatever speed the car is moving at.

I know this is wrong. My question is, why?

Click to expand...

It has to do with the equivalence principle. According to einstein's theories, the laws of physics do not change depending on your frame of reference... the speed you're moving at is considered a frame of reference.

in other words: if a flashlight moving forward at 100 miles an hour, this is exactly equivilent to everytihng in the universe other than the flashlight moving in the opposite direction and the flashlight being stationary.

The problem with this, is how to square that with the speed of light? If the speed of light is always the same, regardless of your frame of reference, then from the flashlight's perspective, the light being projected in front of the flashlight must be going the speed of light relative to the flashlight. If it wasn't then an observer moving with the flashlight, would be able to tell that the flashlight was moving not the rest of the universe, by simply measuring the difference in the speed of light when pointing the flashlight forward as compared to backwards. Similarly, all light eminating from objects other than the flashlight must appear to be moving at light speed as well relative to the flashlight because the speed of light is constant.

So light speed has to move with a speed relative to whatever object is emitting it, but still also has to move at a constant speed (C) regardless of what emitted it or where it was emitted... this would be a contradiction if it wasn't for time dilation and also "pancaking"/"stretching"

to resolve this contradiction, Einstein theorized that time itself will appear to move faster depending on what speed you're going at...

for example, if the flashlight is going half the speed of light, emitting light in front of it... time will fly faster for an observer moving with the flashlight. Since time is going faster, even though the light in front of the flashlight is only going some fraction of the speed of light relative to the flashlight from others' perspectives, from the flashlight's perspective it's going the full speed of light not because the light is faster but because time is flying faster since the flashlight is going so fast.

but that's not all, there's also "pancaking"/"stretching"... objects (and space itself) in front of a fast moving object will appear flatter on the axis that the moving object is moving... conversely, objects behind it will appear stretched out in the direction it came from. That way, if a fast moving object is emitting light behind it AND in front of it, both the light in front and the light behind will be moving at lightspeed relative to the object... the light traveling backwards from a fast moving object will have to travel "farther" to go the same "distance", because everything behind the object is stretched out relative to the fast moving object. Conversely, everything in front of the object is pancaked.

the above is the way the contradiction between having a constant speed of light and the equivalence principle is resolved.

IOW einstein's equivilence principle has a lot of really weird implications and this is one of them.

but it's basically been proven by observation:

keith99 said:

The slam dunk answer is because the speed of light comming from a car or a stationary flashlight or a far away star have all been measured and it is the same.

All else is explaining the observed data. But the data trumps all.

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what he said.

Everything Einstein thought about the equivalence principle would have been completely bunk if it wasn't verified by experimental evidence. But they tested his theory and it actually worked like that, so Einstein had the last laugh.

The speed of light will not change. What will change is the frequency of the light wave. Speed and frequency are not the same. C is constant.