Why can't you go faster than light

[Homer J Simpson]

[digsys]

From the comments ...
" All those interested in time travel, meet here last Thursday. "
:-)

[tggzzz]

Things going faster than light happens all the time. Here's a picture of one example:


Perhaps you want to modify the thread's title?

[Rerouter]

Faster than light in a vacuum, or exceeding "c" is the hard one, Certain experiments have brought light quanta to a complete stop inside a bose-einstein condensate, at that point every motion you make is faster than "that" light

Exceeding "c", that requires abusing weird physics, like a Alcubierre drive,

[nctnico]

Faster than light is relative. There are analog oscilloscopes which sweep the beam across the screen at speeds faster than light.

[TerraHertz]

Things going faster than light happens all the time. Here's a picture of one example:

Physics would be interesting indeed, if c was a local variable.

https://en.wikipedia.org/wiki/Cherenkov_radiation

[tggzzz]

Faster than light is relative. There are analog oscilloscopes which sweep the beam across the screen at speeds faster than light.

No it isn't, and "everybody" does the latter everyday. Well not with an oscilloscope, but with a torch or headlights. The classic pedagogical example is sweeping a torch across the surface of the moon.

As I'm sure you realise, the limit to do with the speed of light (in a vacuum) c relates to particles. When a spot of light moves faster than c, there are no particles moving faster than c.

[JohnnyMalaria]

Faster than light is relative. There are analog oscilloscopes which sweep the beam across the screen at speeds faster than light.

No it isn't, and "everybody" does the latter everyday. Well not with an oscilloscope, but with a torch or headlights. The classic pedagogical example is sweeping a torch across the surface of the moon.

As I'm sure you realise, the limit to do with the speed of light (in a vacuum) c relates to particles. When a spot of light moves faster than c, there are no particles moving faster than c.

Huh?

What is a spot of light vs. particles of light? How can one but not the other exceed the speed of light?

[Gyro]

To quote the great Sir Terry Pratchett:

“Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it.”

[tggzzz]

Faster than light is relative. There are analog oscilloscopes which sweep the beam across the screen at speeds faster than light.

No it isn't, and "everybody" does the latter everyday. Well not with an oscilloscope, but with a torch or headlights. The classic pedagogical example is sweeping a torch across the surface of the moon.

As I'm sure you realise, the limit to do with the speed of light (in a vacuum) c relates to particles. When a spot of light moves faster than c, there are no particles moving faster than c.

Huh?

What is a spot of light vs. particles of light? How can one but not the other exceed the speed of light?

I'll presume you are asking how a spot of light can move faster than c.

Point a laser at a wall 1m away, and rotate yourself so that the spot moves across the wall at 1m/s. Continue rotating as the same angular velocity, but remove that wall and replace it with a building 1km away; by geometry the spot is moving cross the building at 1000m/s. Now rotate at the same angular velocity but point the beam at the moon 384402km away. The beam will move at 384402000m/s across the moon's surface. c is "only" 299792458m/s. QED.

[JohnnyMalaria]

Things going faster than light happens all the time. Here's a picture of one example:


Perhaps you want to modify the thread's title?

That's a case of going faster the speed of light in a material (water) which is not the same as going faster than c.

[tggzzz]

Things going faster than light happens all the time. Here's a picture of one example:


Perhaps you want to modify the thread's title?

That's a case of going faster the speed of light in a material (water) which is not the same as going faster than c.

Well twigged! Did the big hint in my second sentence help you?

[JohnnyMalaria]

Faster than light is relative. There are analog oscilloscopes which sweep the beam across the screen at speeds faster than light.

No it isn't, and "everybody" does the latter everyday. Well not with an oscilloscope, but with a torch or headlights. The classic pedagogical example is sweeping a torch across the surface of the moon.

As I'm sure you realise, the limit to do with the speed of light (in a vacuum) c relates to particles. When a spot of light moves faster than c, there are no particles moving faster than c.

Huh?

What is a spot of light vs. particles of light? How can one but not the other exceed the speed of light?

I'll presume you are asking how a spot of light can move faster than c.

Point a laser at a wall 1m away, and rotate yourself so that the spot moves across the wall at 1m/s. Continue rotating as the same angular velocity, but remove that wall and replace it with a building 1km away; by geometry the spot is moving cross the building at 1000m/s. Now rotate at the same angular velocity but point the beam at the moon 384402km away. The beam will move at 384402000m/s across the moon's surface. c is "only" 299792458m/s. QED.

No, the spot isn't a physical object. There's nothing moving.

https://en.wikipedia.org/wiki/Lighthouse_paradox#Resolution_of_the_paradox_in_special_relativity

[JohnnyMalaria]

Well twigged! Did the big hint in my second sentence help you?

Honestly, I didn't get the second sentence. I assumed I had come to the party late (sub-c travel) and the title had already been changed (if that's even possible)

[RoGeorge]

Nice video, except it doesn't cover the "Why" part from its title. 

[Vtile]

Things going faster than light happens all the time. Here's a picture of one example:


Perhaps you want to modify the thread's title?

Cherenkov radiation. 

[GlennSprigg]

As a possible 'Twist' on the 'suggestion' by TGGZZZ throwing a philosophical spanner-in-the-works  ,
when talking about the 'moving' SPOT of light, (which of course has no speed as such  ).....
I thought I would throw THIS into the thought process, of those that 'ponder' the interesting..........

As an Elect./Tech., I've always hated it when 'people' think/talk about ELECTRICITY moving at light speed !!!!
NOPE !!!!  There is NO correlation !  Yes, a 'signal' may 'appear' almost instantaneously at the other end
of say a 100 mile long wire, but this has nothing to do with it.  Imagine a TUBE filled with say PingPong
balls, and you 'push' one more in one end. The last one 'pops' out the other end, due to resultant forces !
(I know this is an extremely simplified analogy, which varies due to 'many' atomic/electron effects).

Depending on many various factors, I will 'quote' purely an idealized example for the sake of discussion....
A WIRE, carrying a DC current of say 10-Amps at 100v, (actually the voltage is not relevant), MAY only have
the 'Electrons' in it, (electricity is flow of electrons), moving along the 'wire' at about 1 to 10 Millimetres/Sec !!!
It is the CASCADING effect that produces the 'apparent' speed !!!

In fact, for AC, like in your House, be it 50hz or 60hz, the SAME electrons have been 'vibrating' back and
forth within even a short piece of 'cable' indefinitely, and going nowhere 

[tggzzz]

Faster than light is relative. There are analog oscilloscopes which sweep the beam across the screen at speeds faster than light.

No it isn't, and "everybody" does the latter everyday. Well not with an oscilloscope, but with a torch or headlights. The classic pedagogical example is sweeping a torch across the surface of the moon.

As I'm sure you realise, the limit to do with the speed of light (in a vacuum) c relates to particles. When a spot of light moves faster than c, there are no particles moving faster than c.

Huh?

What is a spot of light vs. particles of light? How can one but not the other exceed the speed of light?

I'll presume you are asking how a spot of light can move faster than c.

Point a laser at a wall 1m away, and rotate yourself so that the spot moves across the wall at 1m/s. Continue rotating as the same angular velocity, but remove that wall and replace it with a building 1km away; by geometry the spot is moving cross the building at 1000m/s. Now rotate at the same angular velocity but point the beam at the moon 384402km away. The beam will move at 384402000m/s across the moon's surface. c is "only" 299792458m/s. QED.

No, the spot isn't a physical object. There's nothing moving.

https://en.wikipedia.org/wiki/Lighthouse_paradox#Resolution_of_the_paradox_in_special_relativity

Please don't assume I am saying things that I am not saying. My statements are correct within their limitations - and it is the limitations that expose the sloppy wording/thinking of some other statements. With that in mind...

The spot is indeed moving!

You can see similar things in the heavens, at a larger scale, e.g. https://www.newscientist.com/article/2131889-weird-energy-beam-seems-to-travel-five-times-the-speed-of-light/

[G7PSK]

I have often wondered if the reason we cannot see dark matter is due to it travelling faster than light. That would then pose the question would we ever be able to detect something travelling faster than light.

[tggzzz]

I have often wondered if the reason we cannot see dark matter is due to it travelling faster than light.

Perhaps for the same reason that we can't detect the luminiferous æther?

[donotdespisethesnake]

I don't know about light, but morons always seem to type responses quicker than knowledgeable people can reply

[Rick Law]

Faster than light is relative. There are analog oscilloscopes which sweep the beam across the screen at speeds faster than light.

No it isn't, and "everybody" does the latter everyday. Well not with an oscilloscope, but with a torch or headlights. The classic pedagogical example is sweeping a torch across the surface of the moon.

As I'm sure you realise, the limit to do with the speed of light (in a vacuum) c relates to particles. When a spot of light moves faster than c, there are no particles moving faster than c.

Huh?

What is a spot of light vs. particles of light? How can one but not the other exceed the speed of light?

I'll presume you are asking how a spot of light can move faster than c.

Point a laser at a wall 1m away, and rotate yourself so that the spot moves across the wall at 1m/s. Continue rotating as the same angular velocity, but remove that wall and replace it with a building 1km away; by geometry the spot is moving cross the building at 1000m/s. Now rotate at the same angular velocity but point the beam at the moon 384402km away. The beam will move at 384402000m/s across the moon's surface. c is "only" 299792458m/s. QED.

No, the spot isn't a physical object. There's nothing moving.

https://en.wikipedia.org/wiki/Lighthouse_paradox#Resolution_of_the_paradox_in_special_relativity

Please don't assume I am saying things that I am not saying. My statements are correct within their limitations - and it is the limitations that expose the sloppy wording/thinking of some other statements. With that in mind...

The spot is indeed moving!

You can see similar things in the heavens, at a larger scale, e.g. https://www.newscientist.com/article/2131889-weird-energy-beam-seems-to-travel-five-times-the-speed-of-light/

The spot is indeed moving, however, the spot is not a physical object but an optical reflection.  What moved is not anything on the surface of the moon, but where the reflection (of your moving light beam) occurred.

This is like shooting a billiard ball at one corner of the table and shoot; then from the same spot, aim another ball at another corner of the table.  The two balls hit the rim and reflect back, one following another.  The point where it hits (contacts the rim) moved from one corner to the other - but the table itself did not move, the table rim did not move.  Nothing else physical moved except where the two balls hit.

You can reduce that example further.  With adjustment for gravity and movement, aim one bullet at the left side of the moon, and then aim another at the right side of the moon.  Visually, the spot where the two bullet hits "moved" from the left to the right faster than light.  The crater formed by the bullet-moon collision on the left did not "move" to the right side.  Nothing moved but the two different bullets hitting two different points.

Most important part of not being a physical object is that it has no mass.  Things with zero mass can move as fast as light.  Photon has zero mass but it does carries momentum.

To move faster than light, back to hunting for tachyons, worm holes, or warp-bubbles...

[JohnnyMalaria]

The spot isn't moving because it doesn't exist. All that exists are the photons being scattered by the surface and reaching the observer. If you turned the light off before pointing it at the second location on the moon and then turned it back on, you wouldn't make the same claim, would you? What about if you have the light flash on and off a couple of times? Or a thousand? Or a million? It would make no difference. What if you had two light sources at the same location? One turned on and pointed at one location on the moon and the other turned off and pointed at another. If you switch the first light off and the second one on would you make the same claim about the spot moving?

And what about a shadow? Can a shadow move faster than light? No.

[tggzzz]

The spot isn't moving because it doesn't exist.

If spots of light don't exist, how come they are used in electronic test equipment?

I remember using spot-reflecting ballistic galvanometers in school, to measure charge. An video example of something you think doesn't exist:

You can still buy them:
http://www.bnrexports.com/laboratory-instruments-equipments-suppliers-india.html?cat_id=106

And what about a shadow? Can a shadow move faster than light? No.

Yes it can.

[hamster_nz]

Have a think about what a (tall) person on the moon would see if the spot moved just over 'c'....

With a really high speed camera i think they would see two spots, both moving away from them - one moving away much faster than the other.