It's light Jim, but not as we know it...

[TimberWolf]

Answer me this.

Light particles hit our retinas from the source, at the speed of light, ok? So presumably the light waves must have accelerated to light speed from zero. If so does it take time to accelerate to light speed and how does it know when to stop?

This either a brilliant question or numpy post of the decade...

It doesn't accelerate. I forget the details, but this may be the modern view or may be carp. Everything travels at c through space-time according to relativity. Light has no time-like component and travels through space at c (and experiences no time), while the matter it might have derived from has space and time-like components, and also travels through space-time at c, but the magnitudes of the space and time components are non-zero. So it's more of a change of direction than an acceleration I suppose, but not a change of direction in 3D space.

[TimberWolf]

Almost no voice traffic travels by satellite links, it goes via submarine cables. A particle beam that could travel through the earth would be quicker than light down a cable, due to the shorter route, and potentially a beam of neutrinos wouldn't require repeater stations. It could actually work out cheaper as well as quicker. Question is how do you modulate it if it doesn't really interact with other matter much?

Digital pulses, or energy modulation (which might affect the speed )?

[scooterscot]

Answer me this.

Light particles hit our retinas from the source, at the speed of light, ok? So presumably the light waves must have accelerated to light speed from zero. If so does it take time to accelerate to light speed and how does it know when to stop?

This either a brilliant question or numpy post of the decade...

I don't know.

What I do know is light is the product of two waves, electrical and magnetic, with one of them waves offset by 90 degrees on the z axis.

Also 'light' as we know it must have some minimum amount of energy before it becomes that. If we call that minimum amount of energy 1, then there is no such thing as <1 that we would call light. Is it reasonable to assume by the time 1 is achieved that the photon must already be @ C?

[TimberWolf]

It doesn't accelerate. I forget the details, but this may be the modern view or may be carp. Everything travels at c through space-time according to relativity. Light has no time-like component and travels through space at c (and experiences no time), while the matter it might have derived from has space and time-like components, and also travels through space-time at c, but the magnitudes of the space and time components are non-zero. So it's more of a change of direction than an acceleration I suppose, but not a change of direction in 3D space.

I was beginning to doubt my memory about everything travelling at c in space-time according to relativity, so looked it up (I'm still not confident with the rest of my answer however):

The length of the four-velocity (in the sense of the metric used in special relativity) is always equal to c (it is a normalized vector). For an object at rest (with respect to the coordinate system) its four-velocity points in the direction of the time coordinate.

...

In other words, the norm or magnitude of the four-velocity is always exactly equal to the speed of light. Thus all objects can be thought of as moving through space-time at the speed of light. This provides a way of understanding time-dilation: as an object like a rocket accelerates from our perspective, it moves faster through space, but slower through time in order to keep the four-velocity constant. Thus to an observer, a clock on the rocket moves slower, as do the clocks in any reference frame that is not comoving with them. Light itself provides a special case- all of its motion is through space, so it does not have any "left over" four-velocity to move through time. Therefore light, and anything else travelling at light speed, does not experience the "flow" of time.

Four-velocity - Wikipedia, the free encyclopedia

Of course all this may go by the wayside (and anything else with 'c' in it or done in the last 100 years) if today's announcement turns out to be right.

[d000hg]

Light particles hit our retinas from the source, at the speed of light, ok? So presumably the light waves must have accelerated to light speed from zero. If so does it take time to accelerate to light speed and how does it know when to stop?

Photons and other massless particles are unable to travel at any speed other than light-speed, by definition. Put another way they accelerate infinitely fast because since Force=mass * acceleration ==> a=F/m and if m=0, a is infinite (divide by zero!)

Before you ask why the photon travels at light-speed not infinite speed... due to relativity slowing time and so on, the photon thinks it IS. I think... TW can jump in and correct me but I always think about the reason we cannot accelerate a mass quite to the speed of light is because in its own reference frame, it would be travelling infinitely fast and therefore need infinite energy.

[stek]

I was beginning to doubt my memory about everything travelling at c in space-time according to relativity, so looked it up (I'm still not confident with the rest of my answer however):



Of course all this may go by the wayside (and anything else with 'c' in it or done in the last 100 years) if today's announcement turns out to be right.

So everything is travelling at the speed of light, then maybe the answer to all the time travel conundrums is not to travel beyond the speed of light, but to try and travel slower?

I'm getting a beer from the fridge....

[scooterscot]

So everything is travelling at the speed of light, then maybe the answer to all the time travel conundrums is not to travel beyond the speed of light, but to try and travel slower?

I'm getting a beer from the fridge....

You're already travelling through time.

[stek]

You're already travelling through time.

I've decided to watch Cops with Cameras on Sky Numpty One tonight...

[TimberWolf]

So everything is travelling at the speed of light, then maybe the answer to all the time travel conundrums is not to travel beyond the speed of light, but to try and travel slower?

I'm getting a beer from the fridge....

Ah, but relativity allows you to travel further in your own time than under Newton. Though a side-effect is that everyone ages differently around you when you move relative to them. So in one sense you could traverse the universe within your own life-time (which would be impossible under Newton), but in another realer sense by the time you got there and slowed back down a lot of time would have passed in this new 'inertial frame'. So going less than the speed of light by some small fraction isn't a restriction. Going faster than light...who knows what that's all about.

[OwlHoot]

Quantum effects can also be ruled out based on the spread of times the neutrinos arrive. And the fact that they are always too fast, not sometimes too fast and other times too slow.

True - I was thinking just that while driving back this evening.