Zoom zoom zoom (speed of light question).

[lawtonfogle]

Bob and Andy are brothers. Bob flies a super fast space shuttle (99.9999...%*C), while Andy is a government official and thus sits on earth. Now, when Bob flies past Andy, he emits a few photons (into a vacuum). To Bob, are the photons going C away from him? To Andy, are the photons going C from him?

Text based 'picture':


___<-speed: C-_Photon_____<-speed: ~C-_Bob
_______________________-speed: 0-_Andy___

 

[necroforest]

Yes.

 

[Ectezus]

Bob and Andy are brothers. Bob flies a super fast space shuttle (99.9999...&#37;*C), while Andy is a government official and thus sits on earth. Now, when Bob flies past Andy, he emits a few photons (into a vacuum). To Bob, are the photons going C away from him? To Andy, are the photons going C from him?

Text based 'picture':


___<-speed: C-_Photon_____<-speed: ~C-_Bob
_______________________-speed: 0-_Andy___

Well first of all andy's speed is not zero. The earth is rotating at an incredible speed around our sun. Our solar system is moving at an incredible speed in the spiral arm of our milky way galaxy. This milky way galaxy is moving at an incredible speed in the universe.

But since we all experience the same speed, we also experience the same time and don't notice the effect of this ridiculous speeds. Kinda like how you won't feel any G force when on a car or plain if it's not accelerating or decelerating.

As for the question; yes, light always moves at the speed of light.
If you emit a light beam into space and then move next to it at 99% of the speed of light (like speeding cars on a highway) it will still move away from you at 100% of the speed of light (not 1%)
It's hard to grasp this concept.

- Ectezus

 

[Wiccan_Child]

Bob and Andy are brothers. Bob flies a super fast space shuttle (99.9999...%*C), while Andy is a government official and thus sits on earth. Now, when Bob flies past Andy, he emits a few photons (into a vacuum). To Bob, are the photons going C away from him? To Andy, are the photons going C from him?

Yes. Special relativity starts from the premise that light always travels at c, no matter what inertial frame you're looking from.

 

[Wiccan_Child]

Well first of all andy's speed is not zero. The earth is rotating at an incredible speed around our sun. Our solar system is moving at an incredible speed in the spiral arm of our milky way galaxy. This milky way galaxy is moving at an incredible speed in the universe.

Not quite: we're only moving around the Sun with respect to the Sun. From our point of view (which is just as valid as the Sun's), we're not moving at all.

It doesn't make sense to say that something is moving at a particular velocity, since all velocity is relative to some arbitrary inertial frame.

As for the question; yes, light always moves at the speed of light.
If you emit a light beam into space and then move next to it at 99% of the speed of light (like speeding cars on a highway) it will still move away from you at 100% of the speed of light (not 1%)
It's hard to grasp this concept.

An outside observer sitting on the Earth watching you travel at 99%c and emit a photon would see the photon move at 100%c. This means that it observes you and the photon staying very close together; they would see you moving along, lagging very slightly behind the photon.

However, from your point of view, you're not moving, and the photon zips away at c, and it's the Earth that moves backwards at 99%c.

So, it is 1% .

 

[Ectezus]

Not quite: we're only moving around the Sun with respect to the Sun. From our point of view (which is just as valid as the Sun's), we're not moving at all.

I don't know what you're talking about, we are moving but like I said, without accelerating or decelerating you won't feel it. But any outsider, lets say an alien civilization that watches us will see that we're moving around the sun at high speeds and that sun moves on a spiral arm in our milky way galaxy real fast as well.

But as long as every human being in IN that solar system ON the spiral arm of the galaxy we all experience this as the same speed (aka zero acceleration) and thus have no effect of it, like time dilation.

It doesn't make sense to say that something is moving at a particular velocity, since all velocity is relative to some arbitrary inertial frame.

Actually, we use CMB rest frame for 'local' neighborhoods.

An outside observer sitting on the Earth watching you travel at 99%c and emit a photon would see the photon move at 100%c. This means that it observes you and the photon staying very close together; they would see you moving along, lagging very slightly behind the photon.

However, from your point of view, you're not moving, and the photon zips away at c, and it's the Earth that moves backwards at 99%c.

So, it is 1% .

I was talking about our hypothetical Bob, not Andy. It's not 1% for him. The photon will appear to be going 100% of C away from him.

- Ectezus

 

[shinbits]

As for the question; yes, light always moves at the speed of light.

what about black holes? don't they slow down the speed of the light they draw in?

 

[Wiccan_Child]

I don't know what you're talking about, we are moving but like I said, without accelerating or decelerating you won't feel it.

Exactly: we feel acceleration, but not velocity. The point about relativity is that there is no way, even in principle, to determine absolute velocity (in contrast, you can determine the absolute position or acceleration of an object).

But any outsider, lets say an alien civilization that watches us will see that we're moving around the sun at high speeds and that sun moves on a spiral arm in our milky way galaxy real fast as well.

They'll see the Sun and Earth both orbiting the barycentre. But the point is that the velocity of each object depends on where our hypothetical civilisations are watching from: from the centre-of-mass, they see us moving round them at a particular, constant speed. From the centre of the galaxy, they see our velocities oscillating back and forth, but always much higher than what they would measure at the barycentre. From the Andromeda galaxy, they'd see the Earth-Sun centre-of-mass and the galactic core orbiting their centre-of-mass, and the whole thing would be accelerating away.

The point is that the precise velocity of each object depends on how you define your inertial frame. Things accelerate objectively, but they don't have an absolute velocity. You can pick the Sun's velocity to be anything you like, but inertial frame in which it has that velocity then sets the velocity of everything else.

Yeah.

But as long as every human being in IN that solar system ON the spiral arm of the galaxy we all experience this as the same speed (aka zero acceleration) and thus have no effect of it, like time dilation.

Time dilation also results from velocity. The faster one moves, the slower one's clocks tick, and the shorter one is. But time dilation is a relative effect: the moving object's clocks run slow only with respect to the clocks of the 'stationary' observer.

I was talking about our hypothetical Bob, not Andy. It's not 1% for him. The photon will appear to be going 100% of C away from him.

Ah.

 

[Wiccan_Child]

what about black holes? don't they slow down the speed of the light they draw in?

Light isn't slowed down. It's just that the path its travelling along is tortured and warped. Light can't escape from within the event horizon because its path is so warped that, no matter what direction it's currently pointing, it will eventually get warped back towards the singularity.

Fun .

 

[Ectezus]

what about black holes? don't they slow down the speed of the light they draw in?

Yes, a black hole slows light down a full stop when it hits the black hole itself. The even horizon on the other hand will just warp it towards the black hole, at the speed of light.

 

[Ectezus]

Time dilation also results from velocity.

Thats what I said, but we don't experience any time dilation on Earth because we all move at the same speed in our solar system on the spiral arm of galaxy through the universe.

Exactly: we feel acceleration, but not velocity. The point about relativity is that there is no way, even in principle, to determine absolute velocity (in contrast, you can determine the absolute position or acceleration of an object).

[...]

The point is that the precise velocity of each object depends on how you define your inertial frame. Things accelerate objectively, but they don't have an absolute velocity. You can pick the Sun's velocity to be anything you like, but inertial frame in which it has that velocity then sets the velocity of everything else.

I get what you're saying about 'no absolute velocity', this is basically Einsteins special relativity. But in no way does that mean we can't use logical frames to determine speeds throughout the galaxy.

Like I said before, the part that you skipped: CMB rest frame.
Which as far as I know is the frame where the cosmic microwave background radiation has the same frequency in every direction. I would consider this as fulfilling the criteria for being an absolute reference frame for motion, wouldn't you?

From what I've understood is that in the CMB rest frame we measure no velocity with respect to the CMB photons. So our milky way galaxy is moving 600 km/s + X. That X might be unknown but if it's a constant everywhere it doesn't really matter for using a reference rest frame.

If you want to claim that we can't say anything about certain speeds in the universe because we don't know that X then I'd have to say you're not really being practical.

- Ectezus

 

[shinbits]

Yes, a black hole slows light down a full stop when it hits the black hole itself. The even horizon on the other hand will just warp it towards the black hole, at the speed of light.

Light isn't slowed down. It's just that the path its travelling along is tortured and warped. Light can't escape from within the event horizon because its path is so warped that, no matter what direction it's currently pointing, it will eventually get warped back towards the singularity.

Fun .

Thanx. Much apreciated.

Just one more question.


When a flashlight is turned on in a pitch-black room and then shut off, what happens to the light generated by the flashlight? Sound gets absorbed by the walls or whatever's around; but light seems to just disapear; there's no trace of it. It doesn't (seem to) bounce around for a moment like sound does. Does it also just get absorbed into the walls or surrounding environment like sound does?

 

[Ectezus]

Thanx. Much apreciated.

Just one more question.


When a flashlight is turned on in a pitch-black room and then shut off, what happens to the light generated by the flashlight? Sound gets absorbed by the walls or whatever's around; but light seems to just disapear; there's no trace of it. It doesn't (seem to) bounce around for a moment like sound does. Does it also just get absorbed into the walls or surrounding environment like sound does?

As far as I know light does bounce around like sound does but it is many thousands of times faster so we don't notice the delay/echo effects as much/at all.

On the top of my head I'd say that the light 'energy' get's transferred to either kinetic or heat energy.
Kinda like how black material gets way hotter than white materials. And how we can potentially use solar wind to propel future spacecrafts with a giant solar screen/parachute.

There are probably more forms possible though. (I'd assume radiation but can't say that with 100% certainty)


- Ectezus

 

[Wiccan_Child]

When a flashlight is turned on in a pitch-black room and then shut off, what happens to the light generated by the flashlight? Sound gets absorbed by the walls or whatever's around; but light seems to just disapear; there's no trace of it. It doesn't (seem to) bounce around for a moment like sound does. Does it also just get absorbed into the walls or surrounding environment like sound does?

If we shout on a mountain range, there is a discernible delay between the original sound and its echo. But light is so fast that our brains and eyes cannot distinguish between the two: the echo exists, but we very rarely see it.
Given the distances involved in astronomy, we can see light echoes: a supernova in 2002 seemed, from Earth, to be expanding at a rate far greater than the speed of light (it grew by 7 lightyears in a matter of months!). The explanation involves light echoes: reflection off of the interstellar medium created an optical illusion.

But our flashlight light, like sound, ultimately gets absorbed by the walls of the room (the energy has to go somewhere, after all).

 

[Wiccan_Child]

Thats what I said, but we don't experience any time dilation on Earth because we all move at the same speed in our solar system on the spiral arm of galaxy through the universe.

You mean, because everyone on Earth moves at pretty much the same speed as each other?

I get what you're saying about 'no absolute velocity', this is basically Einsteins special relativity. But in no way does that mean we can't use logical frames to determine speeds throughout the galaxy.

Like I said before, the part that you skipped: CMB rest frame.
Which as far as I know is the frame where the cosmic microwave background radiation has the same frequency in every direction. I would consider this as fulfilling the criteria for being an absolute reference frame for motion, wouldn't you?

No, I would not: measuring velocities with respect to the CMB rest frame only works locally. On Earth, we can construct our model around the CMB rest frame as we see it, and get particular velocities for the Sun, the galactic core, etc. But these only work for our local group: in some far distant galaxy, little blue aliens modelling around their CMB rest frame would see the Sun, the galactic core, etc, moving at different velocities than what we measured.

The CMB rest frame is not a single, universally-applicable rest frame, and so cannot be said to be absolute.

 

[Ectezus]

You mean, because everyone on Earth moves at pretty much the same speed as each other?

Wasn't my post clear enough for you?

No, I would not: measuring velocities with respect to the CMB rest frame only works locally.

Thats what I said on page one.
I'm curious though, do you know any other system to determine speeds in the universe? I'm not aware of any other/better system.

I don't see what your goal here is other than just to argue my first "we move at incredable speeds" comment.

Next time when you enter the thread I'll edit all my posts to say "we move at incredable speeds according to the CMB rest frame" instead. Ok?

- Ectezus

 

[Wiccan_Child]

Wasn't my post clear enough for you?

Obviously not, otherwise I wouldn't be asking for clarification.

Thats what I said on page one.

If it was, then I misunderstood your initial post.

I'm curious though, do you know any other system to determine speeds in the universe? I'm not aware of any other/better system.

With respect to some stationary 'object' (space shuttles are measured with respect to the Earth, the Earth is measured with respect to the Sun or the galactic core, the galaxy is measured with respect to the barycentre of the Local Group, etc).

Have you yourself ever used the CMB as a reference frame?

I don't see what your goal here is other than just to argue my first "we move at incredable speeds" comment.

You seem to be asserting that there exists an inertial that is objective, absolute, and special, and I'm trying to explain that this simply isn't the case.

Next time when you enter the thread I'll edit all my posts to say "we move at incredable speeds according to the CMB rest frame" instead. Ok?

So long as you're not scientifically inaccurate, I couldn't care less.

And no, I'm no so obtuse that I can't understand colloquialisms and shorthand.

 

[Ectezus]

Obviously not, otherwise I wouldn't be asking for clarification.

Then what exactly is it that you don't understand? Because I thought it was perfectly clear.

If it was, then I misunderstood your initial post.

The OP said Andy's speed on Earth was zero. I just added a small reminder that we're actually moving in our galaxy and the universe which is far from zero. You know, something usually overlooked, especially here on this forum.
Then you respond with "It doesn't make sense" and "we're not moving at all". Look, if you want to add a droplet from your fountain of knowledge that's fine, but no need to bash the simple reminder I made which is in fact based on a scientific system.

- Ectezus

 

[Wiccan_Child]

Then what exactly is it that you don't understand? Because I thought it was perfectly clear.



The OP said Andy's speed on Earth was zero. I just added a small reminder that we're actually moving in our galaxy and the universe which is far from zero. You know, something usually overlooked, especially here on this forum.
Then you respond with "It doesn't make sense" and "we're not moving at all". Look, if you want to add a droplet from your fountain of knowledge that's fine, but no need to bash the simple reminder I made which is in fact based on a scientific system.

- Ectezus

You obviously have a problem with me in this thread, no idea why, but you do. So y'know what? I'm outta here.

 

[[serious]]

what about black holes? don't they slow down the speed of the light they draw in?

No. They bend the path of the light until it is unable to escape. There is no slow down of light.