Light Speed

[EC Does It]

I apologise in advance for using the FT forum for this.

Knowing that you TP types have probably forgotten more physics than i will ever know and living in the back of beyond with an extremely dodgy internet connection(otherwise i would spend longer looking)here goes;

In order to settle an (admittedly alcohol induced) contretemps, please could someone explain (preferably in idiot-speak) whether it is possible to exceed lightspeed and if not why not? I just cannot understand why if you accelerate an object continuously, it wont keep on going faster and faster...

And no, im not a trekkie.

Thank you very muchas.

[Cantab12]

Bit of a random question I suppose but here goes:

As a result of travelling faster and faster a body's effective mass will increase so the closer you get to the speed of light the 'heavier' it will become until the mass tends towards infinity.

It has been a couple of years so no derivation or proof I'm afraid but it is part of Einstein's Special Theory of Relativity.

Think of it as trying to lift a dumbell above your head, and the closer you get to locking out your arms people keep piling on weights on the side making it more and more difficult to go up another inch until you get to a tiny distance before locking out and then the mass of the dumbell suddenly increases really quickly becoming effectively infinite making it impossible for you ever to lift it fully.

[Dimensional]

Knew this degree I'm doing would come in useful somehow...

A consequence of Einsten's Theories of Relativity is that mass is not constant with velocity -- the mass of a body is the 'rest mass' (some constant) multiplied by one over the square root of (1 - (v/c)^2) -- in other words, if a body is moving its mass increases, until as the speed approaches 'c' (the speed of light), the mass tends to infinity, because you end up trying to divide by zero.

Therefore, if we apply F = ma (Newton); or more correctly,F = d(mv)/dt, we have that for constant force, the acceleration will tend asymptotically to zero as v tends to 'c'. Or, if you like, you can push your body as hard as you like for as long as you like but the acceleration will still tend to zero.

For a wonderfully simple explanation of this sort of thing, try Richard Feynman's 'Six Not-So-Easy Pieces' (which, despite the title, are remarkably straightforward) -- http://www.amazon.co.uk/exec/obidos/...868995-7395022.

[MarkMcC]

Let's not forget time-dilation and Lorentz contraction (sp??) either...

There was a young lady named Bright,
Who travelled at the speed of light,
She departed one day,
In a relative way,
And arrived on the previous night.

[Matthew Parsons]

Physics geeks should never write poetry.

There once was a fencer named Fisk.
Whose thrust was exceedingly brisk.
So quick was his action,
The Lorentz-Fitzgerald contraction,
Reduced his rapier to a disk.

See what I mean?

It's better not to try to understand why, just accept that you can't exceed the speed of light. Essentially, space and time are inseperable. As you transit through space you also have to transit through time. While we normally travel through time (ie the second hand is always moving), as you travel through space faster than something else you travel through time faster than it as well. What we think of as speed is only how quickly we get between two points. As we reduce the time it takes to get between the points, we also travel faster through time relative to the points, making our speed finite at the speed of light. Like I said, better to just accept it.

You can theoretically get somewhere before a pulse of light that leaves at the same time as you. To do this, you have to change the shape of the space-time around you. This is where Star Trek was leading us with the warp drive. It'll probably never happen, but its a popular thought exercise.

"Six Easy Pieces" is also a good book by Feynman.

[EC Does It]

Cheers Folks,

All of your replies have been extremely helpful as well as very much appreciated.

Happy and safe flying,

ECDI

[SR71]

But what about those particles with imaginary mass but real momentum and energy?

Tachyons?

http://math.ucr.edu/home/baez/physic.../tachyons.html

[john_tullamarine]

Reduced his rapier to a disk.

... foreshortened his foil to a disk is the more common and has a far better metre.

[cwatters]

In order to settle an (admittedly alcohol induced) contretemps, please could someone explain (preferably in idiot-speak) whether it is possible to exceed lightspeed

If this is a pub argument you can tell them YES it is possible and you can do it in you car..... but only if you slow down light....
http://www.hno.harvard.edu/gazette/1....18/light.html
Physicists Slow Speed of Light
By William J. Cromie
Gazette Staff
Light, which normally travels the 240,000 miles from the Moon to Earth in less than two seconds, has been slowed to the speed of a minivan in rush-hour traffic -- 38 miles an hour.
An entirely new state of matter, first observed four years ago, has made this possible. When atoms become packed super-closely together at super-low temperatures and super-high vacuum, they lose their identity as individual particles and act like a single super- atom with characteristics similar to a laser.
Such an exotic medium can be engineered to slow a light beam 20 million-fold from 186,282 miles a second to a pokey 38 miles an hour.

[Gingerbread Man]

Here's the problem I have. Apparently black holes can ingest light because they are so powerful. For this to happen, the light must have some mass, otherwise surely the gravity could not act on it. If the light has mass, it can't travel at the speed of light. Which bit is wrong? I always thought that the black hole would just be absorbing anything that reflected light, which is why they would appear black, but physicists have told me otherwise.

Ginger

[chornedsnorkack]

Originally Posted by Gingerbread Man

Here's the problem I have. Apparently black holes can ingest light because they are so powerful. For this to happen, the light must have some mass, otherwise surely the gravity could not act on it. If the light has mass, it can't travel at the speed of light. Which bit is wrong? I always thought that the black hole would just be absorbing anything that reflected light, which is why they would appear black, but physicists have told me otherwise.
Ginger

Light has mass - but not rest mass. Which is why it always travels at the speed of light.

Another view as to why you cannot exceed the speed of light is to note that the speed of light is in a sense still infinite. As you accelerate towards the speed of light there is the "slowing down" of clocks, and Lorentz contraction. If you measure the distance covered in outside world, with nonmoving ruler, and divide it by time passed for an outside, non-moving and non-slowed clock, the speed is finite and slower than light. But if you divide the distance covered for outside ruler with the time measured by a clock that moves along and is thereby slowed, the result can be however big. So, accelerating towards the speed of light looks like accelerating to an infinite speed.

[Fake Sealion]

A little less high theory but........

Always been fascinated by the fly hitting the car windscreen "puzzle"

Fly going along at 5 mph - car in opposite direction at 40mph.As the fly strikes the car windscreen it must decelerate from 5 to zero and then to 40 in opposite direction...yes? So when plotting it's speed from 5 in one direction to 40 in the other...a some point it must be zero - or stationary? But the car is moving constantly.

[Tim Inder]

Neither the fly or the windscreen of the car are perfectly rigid, they both deform (fly slightly more than the car windscreen!) Imagine diving into a wave- at some point you'll end up going back the way you came, but even though you stop for an instant, the sea doesn't, just a little bit of it!

( I hope that makes sense?!)

[Matthew Parsons]

Black holes capture light by bending space-time into a shape that is geometrically impossible to draw a straight line that both goes into it and exits it. Much like those plastic yellow funnels you can drop coins in and watch them spin around, but you never get your coin back.

[RiskyRossco]

This very closely equates to the "Feckyon Principle", whereby anything you're doing on the computer is important in direct relation to the sudden force of feckyons that attack and screw it up beyond retrieval.
Or the importance of your meeting or appointment is directly proportional to the combination of any factors that gather together - like speeding ticket, roadworks/detours/parades, flat tyre, rain-induced-traffic jams or misplaced car keys - to screw it up.

[Rich Lee]

It has been theorized that Tachyons travel faster than light, as well as other 'imaginary mass' or 'quasiparticles'.

[jamie2004]

-Nothing travels faster than the speed of light.

-No matter how fast you are moving the speed of light seems to be the same speed as if you were not moving at all.

-As an object or person is accelerated toward the speed of light time slows down for it/him.

This last property leads to the "twins" effect: Twin brothers live on Earth. One brother takes a trip to a distant star traveling at a high percentage of the speed of light. When the twin returns he will be younger than his brother because for him time slowed down during the trip.

This effect, called "time dilation," helps explain why the speed of light is the same no matter how fast you are going. As a traveler accelerates time slows down for him. This, in turn, affects his measurements.

hope this leads to a relevant conclusion

[*Zwitter*]

what's the speed of dark?

[PPRuNe Dispatcher]

Here's something to make you think....

The speed of light is 3x10^8 m/s.

The clock rate of a modern microprocessor in a desktop PC is around 3Ghz, i.e. 3x10^9 ticks per second.

That means that every time the clock in a CPU "ticks", a photon would move only 10cm, approximately 4 inches...

[PPRuNe Pop]

Or for simpletons like me: 300,000,000 m/s.