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jack grebe
03-09-2006, 07:41 PM
traveling at the speed of light is said to be impossible, it would take infinate power to do so,right? well light travels at the speed of light. it can be affected by gravity, so it must have mass. in fact it cannot escape a black hole,so it must have mass.sooo how can it travel at the speed of light?

Joe (SoCal)
03-09-2006, 07:43 PM
So if your driving at the speed of light and you turn your headlights on will they work? - Steven Write :D

uncas
03-09-2006, 07:46 PM
Nice Grebe

jack grebe
03-09-2006, 07:47 PM
THANKS :D I think

Paul Pless
03-09-2006, 07:48 PM
Any physicists about?

jack grebe
03-09-2006, 07:51 PM
I prefer this one
[img]http://images.google.com/images?q=tbn:75lUA3TkwkgONM:www.woodenboat.org/festival/Guide/Guide%2520images/grebe.jpg[/ img]

jack grebe
03-09-2006, 07:51 PM
:mad: what happened?

Paul Pless
03-09-2006, 07:52 PM
Don't know why but I'm reminded of an Albert Einstein quote, "Imagination is more important than knowledge. I never came upon my discoveries through the process of rational thought."

[ 03-09-2006, 07:55 PM: Message edited by: Paul Pless ]

Joe (SoCal)
03-09-2006, 07:53 PM
http://www.imagestation.com/picture/sraid105/p108b1a0ab956ac84a8266ef20e262794/f980023f.jpg

http://www.imagestation.com/picture/sraid105/pcdfbd520c4538136fc9a1be8a847b101/f9800241.jpg

http://www.imagestation.com/picture/sraid105/p9e49cfd6035d96990d4bcb69d6c4f1d9/f9800242.jpg

http://www.imagestation.com/picture/sraid105/pb7968419be3bab0d01650d1808393435/f9800243.jpg

http://www.imagestation.com/picture/sraid105/pa5378ebdd53070e5ae4502e3db791f85/f9800247.jpg

http://www.imagestation.com/picture/sraid105/p0f253b5c9eb7f864f2d0fb02e4f12504/f980024b.jpg

jack grebe
03-09-2006, 07:54 PM
try this one
http://images.google.com/images?q=tbn:Kp-IryXbngka4M:www.sss-520-537.com/Photos/Yacht%2520%2520Sea%2520Scout%2520%2 52072%2520ft%2520Grebe%2520.JPG

jack grebe
03-09-2006, 07:54 PM
WHAT AM I DOIN WRONG :mad:

Matt J.
03-09-2006, 08:10 PM
Oh I thought this was a question...

Nevermind. :rolleyes:

Easy answer: There is no current technology which can provide a means to travel at the speed of light.

That certainly doesn't mean it's "impossible"... heck, we're still drill holes in the desert to burn the product for enery!

stumpbumper
03-09-2006, 08:14 PM
So if your driving at the speed of light and you turn your headlights on will they work? - Steven Write Only if your driving in reverse.

Lynn

Victor
03-09-2006, 08:46 PM
Anyone hear about the lady physicist who slowed light down to something like 27 miles an hour? Really!

ljb5
03-09-2006, 09:01 PM
Originally posted by Victor:
Anyone hear about the lady physicist who slowed light down to something like 27 miles an hour? Really!It's even been brought to a dead stop.

The speed of light is only constant in a vacuum -- in a material, it's always slower -- by a factor equal to the index of refraction. That's why light bends when it passes from one material to another.

To answer Jack's question: light has no mass at all. The fact that it is affected by gravity doesn't mean that it has mass --- more like gravity bends space-time around it. Kinda difficulty to picture, but that's the way it is.

As for the question about your headlights.... well, let's say you're traveling at 99.999% the speed of light. If you turn your headlights on, they'll work like normal -- the light will shoot out infront of you at precisely the speed of light.

If you're traveling at almost the speed of light, and the light from your headlights is traveling away from you at the speed of light, you might think that the you add the two speeds together -- so the light is traveling faster than the speed of light.... but that doesn't happen.

You see the light going away from you at the speed of light... and if you passed someone standing still, they'd also see the light traveling at the speed of light -- and you just a little bit slower.

The speed of light is a constant for all observers --everything else is variable -- time, distance, mass, etc...

Two people observing the same thing may see everything totally different --- but the speed of light is always the same for all observers.

Paul Pless
03-09-2006, 09:03 PM
Kinda difficulty to picture, but that's the way it is.
LOL smile.gif Perhaps one day we'll all meet aboard Einstein's train.

[ 03-09-2006, 09:06 PM: Message edited by: Paul Pless ]

JimD
03-09-2006, 09:06 PM
...let's say you're traveling at 99.999% the speed of light... Relative to what (arbitrarily designated stationary object)? ;)

[ 03-09-2006, 09:07 PM: Message edited by: JimD ]

Paul Pless
03-09-2006, 09:07 PM
:D

Fitz
03-09-2006, 09:14 PM
Remember that light acts both like a particle and a wave......

http://t3.preservice.org/T0300715/characteristicsoflight.htm

htom
03-09-2006, 09:21 PM
Jack, it's very difficult to talk about relativity in words.

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html

huisjen
03-09-2006, 10:20 PM
Albert said mass and energy are the same thing. Light has energy, which is mass, sorta, so gravity effects it.

Except that Albert also said mass effects the shape of space-time. Light just follows a straight line along a curved space-time surface, like a golf ball deflecting around a depression in the surface of the putting green, or a coin rolling down one of those funnel things, around and around until the tight spiral at the end where you realize someone else has your money.

Dan

John Gearing
03-09-2006, 10:27 PM
One concept that seems essential to the theory of relativity is "locality". What I mean is that if someone in another galaxy does something it can't instantly affect something here on Earth, because no signal can exceed the speed of light. But there is this funky notion called "spooky action at a distance" that says that under certain circumstances this is exactly what happens. Einstein and some collegues pulled this out of their investigation into quantum mechanics (which Einstein never liked...remember his "God does not play dice" comment) and used it to argue that quantum mechanics must have been flawed or incomplete, because they didn't think their predicted spooky action could happen in reality. But now, decades later, it appears that it can happen. Check the paper at this link:

Spooky action at a distance (http://www.ncsu.edu/felder-public/kenny/papers/bell.html)

huisjen
03-09-2006, 10:33 PM
Quantum Entanglement, the key to teleportation.

Yep. Quantum Mechanics and Relativity don't get along. That's one of the few lasting things I understand from reading Hawking's book. A more accurate explaination is needed. But both theories still work to a large degree. Let the "evolution-is-just-a-theory" weenies take note.

Dan

ingo
03-10-2006, 06:24 AM
Originally posted by Fitz:
Remember that light acts both like a particle and a wave......

http://t3.preservice.org/T0300715/characteristicsoflig ht.htm (http://t3.preservice.org/T0300715/characteristicsoflight.htm)This is not right: Light (photons) are particles and react ALLWAYS as particles. For example one photon never creates an interference pattern. Only the probability function (where the photon is) is a wave.

Back to the first question: Relativity theory does not say that you can not travel with light. It just says that you can not accellerate up to the speed of light since you need unlimited energy in this case. Photos do not accelleryte so they have not a problem - they allways travel with light speed. And if you take the formulas you have another possibility: If you travel FASTER than light ("Tachyons") you can slow down to lightspeed ;)

martin schulz
03-10-2006, 06:28 AM
The answer is:

Improbability drive

http://dvdprime.dreamwiz.com/files/upload/200411/20041113092405840.jpg

[ 03-10-2006, 06:31 AM: Message edited by: martin schulz ]

ingo
03-10-2006, 06:46 AM
I have to watch the movie!

Fitz
03-10-2006, 07:18 AM
Ingo:

How do polarizing sun glasses work?

Popeye
03-10-2006, 08:03 AM
scientists have slowed the speed of light to 0!
http://www.geo.arizona.edu/xtal/nats101/bose-einstein-condensate.jpg

ljb5
03-10-2006, 09:54 AM
Originally posted by JimD:
</font><blockquote>quote:</font><hr /> ...let's say you're traveling at 99.999% the speed of light... Relative to what (arbitrarily designated stationary object)? ;) </font>[/QUOTE]I dunno... Joe asked the question.


Originally posted by huisjen:
Albert said mass and energy are the same thing. Light has energy, which is mass, sorta, so gravity effects it.

Mass and energy are interchangeable, but not the same. Light really doesn't have any mass.

ingo
03-10-2006, 09:58 AM
Originally posted by ljb5:
Mass and energy are interchangeable, but not the same. Light really doesn't have any mass.That is not right: Light has a mass depending on it's wavelength and the number of photons (intensity of light)

ljb5
03-10-2006, 10:01 AM
Originally posted by ingo:
</font><blockquote>quote:</font><hr />Originally posted by ljb5:
Mass and energy are interchangeable, but not the same. Light really doesn't have any mass.That is not right: Light has a mass depending on it's wavelength and the number of photons (intensity of light)</font>[/QUOTE]Nope.

jack grebe
03-10-2006, 10:01 AM
so if light has mass, traveling at the speed of light is possible because light can

ingo
03-10-2006, 10:08 AM
Originally posted by Fitz:
Ingo:

How do polarizing sun glasses work?This is a very good question. You need some quantum electrodynamics to describe it in the right way. I would suggest Richard P. Feynmans book "QED: The Strange Theory of Light and Matter" since it is written for normal human beeings.
I can't give you a short nor an understandable answer. Even the electrodynamic answer is not simple and in general you do not have linear polarised fields but eliptical polarised ones.

In the evening I will have a closer look in some books. But to say it in general: The probability function is filtered, and without a probability you have no light :D

ljb5
03-10-2006, 10:12 AM
Originally posted by jack grebe:
so if light has mass, traveling at the speed of light is possible because light canNo, seriously, light doesn't have any mass at all.

None.

It has an 'effective mass,' but that's not a true mass, just a ratio of momentum and velocity. (Anything can have an 'effective mass' and this effective mass can change depending on condtions and can even be negative. It's not a true mass at all, just a form of short-hand to describe its current condition.)

The true mass of a photon is given by:

m^2=(E^2/c^4)-(p^2/c^2)

Since E=pc, m=0.

[ 03-10-2006, 10:18 AM: Message edited by: ljb5 ]

ingo
03-10-2006, 10:19 AM
Originally posted by ljb5:
</font><blockquote>quote:</font><hr />Originally posted by ingo:
</font><blockquote>quote:</font><hr />Originally posted by ljb5:
Mass and energy are interchangeable, but not the same. Light really doesn't have any mass.That is not right: Light has a mass depending on it's wavelength and the number of photons (intensity of light)</font>[/QUOTE]Nope.</font>[/QUOTE]Yes! The mass of a photon is simply calculated by m=e/c^2 or m=(h*f)/c^2

f=frequency of the light
h=Planck's constant=6.626 * 10^-34 Joule seconds

Light has even a pressure to objects and there are some ideas for using this in moving spaceships.

ingo
03-10-2006, 10:23 AM
Originally posted by ljb5:
</font><blockquote>quote:</font><hr />Originally posted by jack grebe:
so if light has mass, traveling at the speed of light is possible because light canNo, seriously, light doesn't have any mass at all.

None.

It has an 'effective mass,' but that's not a true mass, just a ratio of momentum and velocity. (Anything can have an 'effective mass' and this effective mass can change depending on condtions and can even be negative. It's not a true mass at all, just a form of short-hand to describe its current condition.)

The true mass of a photon is given by:

m^2=(E^2/c^4)-(p^2/c^2)

Since E=pc, m=0.</font>[/QUOTE]Sorry, but what should be a "true mass"? Mass is mass is mass. This is the thing that reacts on gravitation. And of course photons react on gravitation. Simple example: The black hole. It's so heavy that photons can't leave the orbit/surface.

ljb5
03-10-2006, 10:27 AM
Originally posted by Fitz:
How do polarizing sun glasses work?Light is composed of two waves, an electric wave and a magnetic wave, oriented at a right angle.

http://www.monos.leidenuniv.nl/smo/basics/images/wave.gif

When light hits a material, the electric and magnetic waves interact with the electrons of the material. If the material has some structure so that the electrons lie in a pattern which is not the same in all directions, the electric waves of light will hit those electrons differently -- this changes how they bounce off.

Polarizing sunglasses have a polymer coating. The polymer is composed of long, thin chains of atoms. The polymer is stretched so that in one direction that atoms are in long, straight lines and in the other direction (90 degrees away), the are in a short, broken arrangement.

Normal light is unpolarized, so it contains a mix of photons pointing in all directions. When this hits the polarizer, some get knocked out by the electrons of the polymer and others slip right through.

PatCox
03-10-2006, 10:30 AM
The reason the light from your headlights will be travelling at the speed of light is because your velocity warps both space and time for you, if you are moving at near the speed of light; time, for you, will be very slow, and space will be warped in a way that compresses distance, as observed by someone else, of course, not that you'd notice. So, the light leaving your headlight would be travelling in your time and your space at the speed of light according to your measurement, though your time is slower than a "stationary" observer's time, and your space is shorter, too (your mile would actually be much longer than the mile seen by an observer). And thats why the same observer would also measure the speed of the light from your headlights as having the same velocity that you'd measure it at, in his measurements, because his time is much faster, and his space is different too. Though I might have the contraction effect backwards; can I remember this, is that the Lorentz contraction, is that related to a lorentze transform? TimeR = one over the square root of c squared minus velocity squared, distance R = 1 over the square root of c squared minus velocity squared, where timeR and distanceR are the time and distance of the moving object, c is the speed of light, and velocity is the velocity of the moving object, something like that? Plug those equations into maxwells equation and simplify and you get e=MC squared, I believe.

PatCox
03-10-2006, 10:33 AM
Look at a blue sky through your polarized lens and tilt your head 90 degrees, the sky will brighten up considerably.

ingo
03-10-2006, 10:33 AM
lib5, the question was not, how polarisation works, the question was how it works in QED where the photon is (more or less) a particle. Classic particles do not care of the directions of polymers...

jack grebe
03-10-2006, 10:37 AM
my head hurts

Popeye
03-10-2006, 10:37 AM
Ingo dude,

for a classic quantum harmonic oscillator the rest mass for a photon is zero , what you are refering to is the 'Mossbauer Effect' causing apparent momentum and mass effects , but to find the energy eigenstates, you would first need to solve the time-independent Schrödinger wave equation

ready?

[ 03-10-2006, 10:38 AM: Message edited by: popeye ]

ljb5
03-10-2006, 10:39 AM
Originally posted by ingo:
Sorry, but what should be a "true mass"? Mass is mass is mass.True mass is invariant mass (http://en.wikipedia.org/wiki/Invariant_mass). It's not the same as relativistic mass or effective mass or active or passive gravitational mass. (http://en.wikipedia.org/wiki/Mass#Relativistic_relation_among_mass.2C_energy_an d_momentum)

Light has momentum -- which may be useful to move spaceships and is definitely useful to make those little things spin inside a glass bulb on a sunny window sill.... but momentum is not mass and does not imply the existance of mass.

E=mc^2 does not mean that energy has mass -- it means that energy may be converted to mass.

(In fact, this happens when photons form electrons, positrons and neutrinos -- but when that happens, the photon is annhilated.)

If you want to talk about gravitational effects, you must recognize that special relativity (E=mc^2) does not apply to gravity and cannot be used.

In talking about gravity, you must use general relativity, not special relativity -- and the math gets a lot harder.

E=mc^2 is only a partial answer (just like F=ma is good enough for many situations, but not all). For massless particles, like photons, use E=sqrt(m^2c^4+p^2).

[ 03-10-2006, 10:49 AM: Message edited by: ljb5 ]

George.
03-10-2006, 10:42 AM
:D

This thread is a riot...

ingo
03-10-2006, 10:48 AM
Originally posted by PatCox:
... Plug those equations into maxwells equation and simplify and you get e=MC squared, I believe.No, you get c out of maxwell but it has nothing to do with mass. Maxwell is special relativity theory, everything with mass is general relativity theory.

cedar savage
03-10-2006, 10:52 AM
Originally posted by George.:
:D

This thread is a riot...Verra enlightening, arrrr?

ingo
03-10-2006, 11:05 AM
Originally posted by popeye:
Ingo dude,

for a classic quantum harmonic oscillator the rest mass for a photon is zero , what you are refering to is the 'Mossbauer Effect' causing apparent momentum and mass effects , but to find the energy eigenstates, you would first need to solve the time-independent Schrödinger wave equation

ready?Yeah, but we did this in the third semester. Ready for QED and string theory?

Mößbauer (i am aware that your keyboard has too less characters like ö and ß) and solid state physics (like his crystals) are not neccessary to explain the mass of a photon. The point with the Mößbauer effect is that the complete crystal can absorb the momentum and you have "elastic impacts" compared to "inelastic impacts" that you get when single atoms react with photons and the photons change their energy. Its like billard: when two balls react, both change their energy. But if a ball hits a wall it does change only the direction, not the energy.
Of course it is a little more complex on a quantum level and that is why Mößbauer got a nobel price for it :D

ingo
03-10-2006, 11:23 AM
Originally posted by ljb5:
</font><blockquote>quote:</font><hr />Originally posted by ingo:
Sorry, but what should be a "true mass"? Mass is mass is mass.True mass is invariant mass (http://en.wikipedia.org/wiki/Invariant_mass). It's not the same as relativistic mass or effective mass or active or passive gravitational mass. (http://en.wikipedia.org/wiki/Mass#Relativistic_relation_among_mass.2C_energy_an d_momentum)

Light has momentum -- which may be useful to move spaceships and is definitely useful to make those little things spin inside a glass bulb on a sunny window sill.... but momentum is not mass and does not imply the existance of mass.

E=mc^2 does not mean that energy has mass -- it means that energy may be converted to mass.

(In fact, this happens when photons form electrons, positrons and neutrinos -- but when that happens, the photon is annhilated.)

If you want to talk about gravitational effects, you must recognize that special relativity (E=mc^2) does not apply to gravity and cannot be used.

In talking about gravity, you must use general relativity, not special relativity -- and the math gets a lot harder.

E=mc^2 is only a partial answer (just like F=ma is good enough for many situations, but not all). For massless particles, like photons, use E=sqrt(m^2c^4+p^2).</font>[/QUOTE]Please not that invariant mass is not the same as rest mass. The rest mass of a photon would be zero (but they never rest). Since they move in any inertial system with lightspeed their relativistic mass is an invariant mass!

And of course a electro magnetic field has a REAL mass. It's normally very small but at the surface of pulsars it can for example reach 200g/cm^3. This real mass has to be included in the gravitation fields or you get wrong results.

Tealsmith
03-10-2006, 11:31 AM
Jack Handey

"If you go flying back through time and you see somebody else flying forward into the future, it's best to avoid eye contact."

jack grebe
03-10-2006, 11:42 AM
ROTFLMAO :D

Popeye
03-10-2006, 12:08 PM
coupla things to remember here:

1. Einstein said , forget what you know and forget what you think you know

2. never add pineapple juice to your jello mould , because the jello just won't set if you do

Popeye
03-10-2006, 12:11 PM
The rest mass of a photon would be zero (but they never rest). except possibly in a Bose-Einstein Condensate and inside black holes

ibid

Popeye
03-10-2006, 12:19 PM
This real mass has to be included in the gravitation fields or you get wrong results either quantized energy packets have zero mass or QM is out the winda

Popeye
03-10-2006, 12:28 PM
Ready for QED and string theory?i can see you have a dizzying intellect

[ 03-10-2006, 02:58 PM: Message edited by: popeye ]

ingo
03-10-2006, 12:42 PM
Originally posted by popeye:
</font><blockquote>quote:</font><hr />The rest mass of a photon would be zero (but they never rest). except possibly in a Bose-Einstein Condensate and inside black holes

ibid</font>[/QUOTE]Since all particles in a Bose-Einstein Condensate are totally delocated, it makes no sense to define something like "speed". Same with singularities like black holes.

ingo
03-10-2006, 12:52 PM
Originally posted by popeye:
</font><blockquote>quote:</font><hr /> This real mass has to be included in the gravitation fields or you get wrong results either quantized energy packets have zero mass or QM is out the winda</font>[/QUOTE]QM is wrong. You need QED. Or something even better like QCD (quantum chromo dynamics)or the GUT (great unifying theory).

Tealsmith
03-10-2006, 01:41 PM
Vizzini: I can't compete with you physically, and you're no match for my brains.
Westley: You're that smart?
Vizzini: Let me put it this way. Have you ever heard of Plato, Aristotle, Socrates?
Westley: Yes.
Vizzini: Morons.

George Roberts
03-10-2006, 02:00 PM
I thought I might learn something.

... And then I realized this discussion was being written by a bunch of wooden boat builders.

Never confuse QED with reality.

ingo
03-10-2006, 02:01 PM
:D :D
Ok, we should stop it. And in fact I have just a limited knowledge of general relativity and made my diploma in theoretical electrodynamics. And that was 12 years ago...

ingo
03-10-2006, 02:05 PM
Originally posted by George Roberts:
I thought I might learn something.

... And then I realized this discussion was being written by a bunch of wooden boat builders.

Never confuse QED with reality.No, what allways counts is the reality, not the theory. Deep in their heart even theoretical physics accept this smile.gif But QED is one of the finest theories to match reality and much better than Newton, qm and especially Intelligent Design...

jack grebe
03-10-2006, 02:06 PM
are you kiddin....two pages of crap that no one knows anything about :D

ingo
03-10-2006, 02:11 PM
How does a physicist proof that all uneven numbers are prime?

3
5
7
measuring error
11
13
...

Popeye
03-10-2006, 02:11 PM
Originally posted by ingo:
(great unifying theory).that and more stuff and things

[ 03-10-2006, 02:16 PM: Message edited by: popeye ]

ingo
03-10-2006, 02:14 PM
Originally posted by jack grebe:
are you kiddin....two pages of crap that no one knows anything about :D No! I am right ;) Really. But please don't force me to go to the book shelf and proof it. Its 8pm here and I just opened a bottle of wine and have to update the forum-software of two yacht clubs in the next hours...

ljb5
03-10-2006, 03:30 PM
Ingo, I have been unable to find any reference in QM or QED that says photons have mass.

E=pc
E=sqrt(m^2c^4+p^2c^2)

Looks to me like m=0.

Here's a decent explanation. (http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html)

George Roberts
03-10-2006, 03:32 PM
ingo ---

"But QED is one of the finest theories to match reality and much better than ... Intelligent Design..."

But only because neither you nor I studied Intelligent Design in college.

[ 03-10-2006, 03:33 PM: Message edited by: George Roberts ]

ingo
03-10-2006, 04:07 PM
Originally posted by ljb5:
Ingo, I have been unable to find any reference in QM or QED that says photons have mass.

E=pc
E=sqrt(m^2c^4+p^2c^2)

Looks to me like m=0.

Here's a decent explanation. (http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html)Okay: Back to the roots: What is mass?

Photons have momentum and react on gravity. What do you expect more of a particle to have a mass?

George.
03-10-2006, 04:40 PM
I can't believe this discussion...

ljb5
03-10-2006, 06:48 PM
Originally posted by ingo:
Photons have momentum and react on gravity.So what? Momentum is not mass.


What do you expect more of a particle to have a mass?</font> The ability to accelerate when a force is applied (it doesn't have to be F=ma, but some function of F)</font> The ability to decelerate by emitting a photon</font> The ability to generate a gravitational field</font> And the big one.... the inability to travel at the speed of light.</font>

Meerkat
03-10-2006, 06:55 PM
It's all quantum foam to me. ;)

JimD
03-10-2006, 08:37 PM
...if you are moving at near the speed of light... Again I ask, moving near the speed of light relative to what? The whole point of Relativity Theory is that motion is relative. Otherwise Albert would have called it something else (or be intentionally misleading). Any object can be found to be moving relative to any other arbitrarily designated object said to be standing still in relation to it. Its all about choosing a convenient reference point from which to measure velocity. Say, this is a fun thread in a really silly sort of way :D

[ 03-10-2006, 08:46 PM: Message edited by: JimD ]

jack grebe
03-10-2006, 09:34 PM
I have a feeling that this is gonna keep ingo awake tonite :D

Paul Pless
03-10-2006, 09:39 PM
I can't believe this discussion... I'm a little dumbfounded myself. Not by the physics, but by the fact that this discusion is being held here. I don't even think the old bilge was privy to a serious relativity thread.

jack grebe
03-10-2006, 09:42 PM
at least it's not 35 pages about kat :D

[ 03-10-2006, 09:43 PM: Message edited by: jack grebe ]

George Roberts
03-11-2006, 08:55 AM
As I sit here watching my TV I note that I am moving at the speed of light relative to the photons from that TV.

World's fastest human. And science says I cannot be beat (except with a stick).

ljb5
03-11-2006, 09:32 AM
Originally posted by JimD:
</font><blockquote>quote:</font><hr /> ...if you are moving at near the speed of light... Again I ask, moving near the speed of light relative to what?</font>[/QUOTE]Jim, the question is patently impossible, so it never shoud have been asked -- and it's rather pointless to speculate about what it means....

Nevertheless, I think the answer is 'relative to any observer anywhere in the universe.'

And then the answer, of course, is that you cannot move at the speed of light relative to anything (other than light).

If you were on a west-bound train moving at 60% the speed of light (relative to the track), and you passed an east-bound train moving at 60% the speed of light (relative to the same track), you might think that you would be moving at 120% the speed of light relative to the other train --- but alas, that's not the case...

ingo
03-11-2006, 11:36 AM
Originally posted by ljb5:
</font><blockquote>quote:</font><hr />What do you expect more of a particle to have a mass?</font> The ability to accelerate when a force is applied (it doesn't have to be F=ma, but some function of F)</font> The ability to decelerate by emitting a photon</font> The ability to generate a gravitational field</font> And the big one.... the inability to travel at the speed of light.</font></font>[/QUOTE]The only natural expectation is that a photon should be able to create a gravitational field. The other three are artifical caused by your knowledge of the theory.
As far as I understood general relativity, photons do create a gravitational field. The main point in Einsteins theory is the energy-momentum tensor and since photons have both they influence the spacetime.

But perhaps there are more important topics to talk about and it seems that the others don't really follow the discussion smile.gif

ljb5
03-11-2006, 11:40 AM
Originally posted by ingo:
The other three are artifical caused by your knowledge of the theory.Yup, my knowledge of the theory causes a lot of things. smile.gif

George.
03-11-2006, 11:44 AM
Now wait a second. If photons had mass in the ordinary sense and created a gravitational field, they wouldn't just be attracted to stars and black holes. They would be attracted to each other.

That would make for all sorts of interesting effects on the light of distant galaxies, as the beams of light coming from them would in effect generate their own gravitational lens... ;)

ljb5
03-11-2006, 11:50 AM
Originally posted by George.:
Now wait a second. If photons had mass in the ordinary sense and created a gravitational field, they wouldn't just be attracted to stars and black holes. They would be attracted to each other.Very true.

They also would bounce off each other -- but that never happens. Photon pass directly through each other and never experience photon-photon scattering.

ljb5
03-11-2006, 12:31 PM
I think some of this confusion can be cleared up by looking at the exact nature of gravity's effect on light.

I don't think it's correct to say that gravity interacts with photons. "Interacts" implies a two-way street -- like an equal and opposite force. As the sun attracts the earth, the earth attracts the sun (to a much smaller, but very real amount).

As far as I have been able to determine, photons do not have any gravity of their own. They may be effected by a heavy object, but they do not have any equal or opposite effect back on that object.

If we look more closely at gravity's effect on photons, we see that there really isn't much there. Gravity doesn't move the photon at all -- it bends space-time around the photon, but leaves the photon untouched.

As far as the photon is concerned, it moves in a perfectly straight, undisturbed line. Except that line happens to lie inside something that appears curved to a distant observer.

In fact, from the photon's perspective, it's the only thing moving in a straight line and everything else in the universe has been warped.

paladin
03-11-2006, 04:31 PM
...but....but...if you were travelling at the speed of light or faster how could you see a BIG PLANET in your way before crashing into it....

ingo
03-11-2006, 04:42 PM
Originally posted by paladin:
...but....but...if you were travelling at the speed of light or faster how could you see a BIG PLANET in your way before crashing into it....Well, photons crash in planets. That's why we can see them :D

Meerkat
03-11-2006, 04:44 PM
tachyon

A hypothetical subatomic particle that always travels faster than the speed of light.Perhaps not so hypothetical: Cherenkov radiation is/may be caused by tachyons.

Microwaves have been observed with an apparent speed 4x that of light.

Neutrinos have recently been discovered to have mass, which surprised the hell out of the physics crowd with whom the massless neutrino had been a given for 80+ years. Blew something called "the standard model" right out the window.

Remember, Einstein's theory is just that: a theory. It has holes and is probably not the definitive theory. We're up to 19 diminsions now and I don't think that was in Albert's thinking way back when.

I wish they'd hurry up with that warp drive... ;)

ingo
03-11-2006, 05:27 PM
Meer, there are no tachyons (found yet), the standard model is still much more valid than Newton and Einsteins theories are one of the finest we have. Of course there are still things that these theories can't explain. If they could explain everything, we would not need physicists or god any more :D

Meerkat
03-11-2006, 06:06 PM
I thought some work at least suggested Cherenkov radiation might be caused by tachyons.

Let's keep the physicists - god is a myth. ;)

ljb5
03-11-2006, 07:08 PM
Originally posted by Meerkat:
Microwaves have been observed with an apparent speed 4x that of light.I'd like to know more about this.

Years ago, some of my coworkers got fired up about a report (in the New York Times, I think) about faster-than light travel.

We looked into it and, of course, it was bunk.

PatCox
03-11-2006, 10:08 PM
Something travels faster than the speed of light, according to my physicist friend. Apparently there is one particular experiment in particle physics in which a subatomic particle, I don't know which, is broken down into two examples of another subatomic particle, I don't know the name of that one either. But when this happens, one of the two resultant particles has one color or spin or flavor or something, and the other has another color or spin or whatever. But whatever that characteristic is, its possible to change it. And in an experiment, scientists have changed the characteristic of one of the two resultant particles, and when they do, the other one switches, so that there are still one of each variety.

And what I am told is that this happens instantaneously, regardless of how far apart the two particles are. So something communicates between these particles at faster than the speed of light.

Now I am only a reader of popular explanations of this sort of thing, and I may have it wrong, so do any of you experts know about this one, can you explain further?

Meerkat
03-11-2006, 10:14 PM
Originally posted by ljb5:
</font><blockquote>quote:</font><hr />Originally posted by Meerkat:
Microwaves have been observed with an apparent speed 4x that of light.I'd like to know more about this.
</font>[/QUOTE]google pulls up 1.7 million hits on "microwaves faster than light" (no quotes).

Here's one:
Light pulses flout sacrosanct speed limit

Peter Weiss

Five years ago, a wave of discontent swept away the 55-mile-per-hour U.S. speed limit. Nowadays, some physicists are taking a hard look at the 670-million-miles-per-hour speed limit of light in a vacuum, or c.

Albert Einstein posted this limit in his 1905 theory of special relativity. Although popular lore and some physics textbooks still contend that nothing races faster than c, experiments going back decades have repeatedly shown that light can beat that speed under certain conditions.

A few scientists argue that those experiments hint that Einstein was wrong. Two new experiments reveal dramatic additional evidence of superluminal velocity but make no clear case for repealing Einstein's law, scientists say.

In one study, conducted in Italy, scientists propagated superluminal microwaves through air by bouncing them off a mirror. In the other, led by a New Jersey researcher, a laser pulse approaching a gas-filled cell's entry window materialized at the cell's exit glass before even reaching the cell.

Although superluminal phenomena might someday help speed up computers—an avenue being explored by Raymond Y. Chiao of the University of California, Berkeley—the main excitement around these experiments stems from basic physics implications.

At stake is the idea that a cause must precede an effect. If experimenters found that information can go somewhere faster than c, "you would get into nonsensical types of predictions, like going back in time and shooting your grandmother," explains Peter W. Milonni of Los Alamos (N.M.) National Laboratory.

Günter Nimtz of the University of Cologne in Germany contends that information can indeed travel faster than c, casting doubts on both causality and special relativity. In 1995, for example, his research team encoded Mozart's 40th symphony in a microwave beam traveling at 4.7 times c to a receiver.

However, Aephraim M. Steinberg of the University of Toronto argues that aside from Nimtz and a few other "vocal dissenters," mainstream physicists agree that such experiments "do not support any idea of causality violation." One challenge, however, is to exactly define information, or a signal.

Experiments dating back to the early 1990s by Nimtz, Steinberg, Chiao, and others have shown superluminal tunneling of optical photons through mirrors (SN: 7/2/94, p. 6) and of microwaves through so-called forbidden zones of waveguides.

The Italian scientists, led by Anedio Ranfagni of the Italian National Research Council in Florence, devised their experiment so that reflected microwaves in open air overlap and interfere as the waves speed away from the mirror. Constructive interference creates a moving pulse along the axis of the apparatus whose speed varies according to the configuration of the experiment. The researchers report in the May 22 Physical Review Letters that within 1.4 meters of the mirror, they clocked such pulses at up to 125 percent of c. Beyond that distance, the effect dies out.

Because electromagnetic waves radiate through air much as they do in a vacuum, Chiao says, the "spectacular work" by the Italians demonstrates that even in a vacuum, light could outpace c.

In the laser experiment by Lijun Wang of NEC Research Institute in Princeton, N.J., and his colleagues, the superluminal pulse, which was preceded by a "pump" pulse to excite the amplifier, has a negative velocity. That means that it "arrives at a distant point 'earlier' than it even arrives at the input," explains Steinberg, who is acquainted with the unpublished study but is not a coauthor.

This isn't magic, he says. Rather, amplifiers, like the cell in the experiment, respond to certain frequencies by building a replica of the incoming pulse at the output. In this case, the time a pulse with speed c would take to cross the cell, multiplied by 300, is the head start the outgoing pulse gains over the incoming one.

What's more, any rounded pulse contains a central peak and tapering wings extending far out behind and ahead. The wings contain all the information needed to reconstruct the peak, so as soon as the forward wing of the incoming laser pulse arrives, the cell spits out a full-scale version of the peak.

Although Wang declined to discuss the study, which was submitted to Nature, some of its results were described May 30 in The New York Times.

ingo
03-12-2006, 04:40 AM
There are different types of "velocity". Some move faster than lightspeed. The problem is if they can carry any "information". (Sorry, this is too complicated for this forum and I am not used to translate this stuff to english. So I have to stop here :( )

Anyway the speed of light in matter is sometimes higher than in a vacuum!

ljb5
03-12-2006, 10:27 AM
Pat, you actually did a pretty good job of describing the EPR (Einstein-Podolosky-Rosen)experiment, commonly called "Spooky action at a distance."

This is the experiment which offers the best hope of faster-than-light travel, yet still there is no agreement. One of the problems in the experiment is that nothing is actually traveling between the two particles. It's not like one particle emits something which travels a distance and then the other particle absorbs it.

What occurs is the simultaneous resolution of superimposed quantum states. Coordination without communication. One way to think about it is that the two particles, although separate, are still actually the same particle - just as they were at the beginning of the experiment. It just happens to be very, very delocalized.

At best, in the EPR experiment one could say there has been faster-than-light transmission of a quantum state. But one cannot claim to have transmitted anything such as mass or energy over that distance -- and nothing at all traveled from one place to the other.

<hr>Meerkat, the microwave experiment you described is a common source of confusion. The problem, as Ingo points out, is that there are different types of velocity -- but not all transmit real information. In this case, someone has confused phase velocity or group velocity with true velocity.

There are a couple of simple experiments that illustrate the problem. Imagine you are shining a laser pointer on a movie screen from 100 feet away. By making a small motion of your wrist, you can cause the laser dot to move very fast from one side of the screen to the other. Now, if you move that screen very far away (lets say to the moon, or perhaps a light year away), the same small motion of your wrist will result in a much larger motion of the laser dot.

In fact, if that screen were one light-year across, but so far away that you can scan from the left to the right edge with just a flick of your wrist, you'd see that laser dot move a full light year in a fraction of a second -- very much faster than the speed of light!

But you must ask yourself what is really moving? What is the laser dot? It's nothing. The true movement is the light coming out of your pointer, hitting the screen and reflecting back to you.

The second experiment you can observe at the beach. Imagine a steady stream of waves coming into the beach at almost exactly a 90 degree angle. At the edge of the beach is a low wall so that when the wave hits, it sends up a splash of foam.

If the wave hits at exactly a 90 degree angle, the entire wave will hit the wall at once, sending up a uniform splash. If the wave comes in at 45 degree angle, the splash will start when one edge of the wave first hits, and then travel along the wall at sqrt(2) times the speed of the wave.

If the wave comes in at almost 90 degrees, you will see the splash start at one end and travel very, very fast to the other end of the beach.

But again, you have to consider what is actually doing the traveling. The splash is nothing. The only thing that is actually traveling is the wave and that's only moving in one direction, not along the length of the wall.

<hr>Ingo, when you say the speed of light can be higher in a material than in a vacuum, I think you are referring to Negative Index materials or left-handed materials.

These materials are awfully confusing, but do not cause the speed of light to increase. (http://physicsweb.org/articles/news/7/3/12)

I think the best way to describe it is to say that when light enters the material, the end of the signal emerges before the beginning. This means that the end of the signal traveled faster than the start --- not because it traveled faster than the speed of light but because the start of the signal was delayed.

[ 03-12-2006, 10:52 AM: Message edited by: ljb5 ]

Bruce Taylor
03-12-2006, 11:43 AM
Great thread!

Meerkat
03-12-2006, 04:34 PM
We aren't going to know for sure until we have the GUT and maybe even that won't be the final answer. ;)

jack grebe
08-20-2017, 03:34 PM
Some rather interesting fellows from bygone days.......



Any newer folks want to weigh in?????

Tom Montgomery
08-20-2017, 05:25 PM
traveling at the speed of light is said to be impossible, it would take infinate power to do so,right? well light travels at the speed of light. it can be affected by gravity, so it must have mass. in fact it cannot escape a black hole,so it must have mass.sooo how can it travel at the speed of light?You are asking how light can travel at the speed of light? :confused:

As for gravity "bending light"... a massive object (like a black hole) is actually bending the fabric of spacetime. That is what gravity is. It is spacetime that is being affected. Light has no mass. Light is simply traveling the shortest distance between two points within the curved fabric of spacetime. For the same reason the earth orbits the sun.

No particle containing mass can travel at the speed of light. As a particle containing mass approaches the speed of light its mass increases to infinity. It would take an infinite amount of energy for a particle with mass to achieve the speed of light.

Seems pretty simple to me. And predictions of the theory have been confirmed over and over again without fail.

Gerarddm
08-20-2017, 05:55 PM
That woman admiral Grace Whatishername was an early computer pioneer ( she coined the term 'bug' to describe a computer malfunction ) one gave a speech where she illustrated the speed of light by holding up a copper rod that was maybe around 3 feet or so in length. This is how far light travels in a nanosecond, she said.

Jim Mahan
08-20-2017, 06:11 PM
Why pop up this thread from '06?

Tom Montgomery
08-20-2017, 06:19 PM
For some reason ljb5 didn't convince Jack.

21st century Reds tend to have difficulty with science.

webishop14
08-20-2017, 07:24 PM
Uh, Jack --

I think the answer should be obvious. If I'm driving my Volvo down the turnpike at 50 miles and hour, and it can't go any faster than that, perhaps that's the speed of Volvo. I suspect that light is pedaling as fast as it can, and that's the speed it's traveling at: the speed of light.

john welsford
08-20-2017, 08:17 PM
Something interesting that I've not got the math to get my head around, is that the speed of light is a "local constant". That is, light emitted by two different sources, one travelling toward the point of observation, and the other away, arrives at the p.o.observation at the same speed but blue or red shifted accordingly.

That said, imagine, if a spaceship were to accelerate up to say 2/3 lightspeed, rendezvous with an object travelling away from her point of departure at that speed, then accelerate away from that object to a speed relative to that of 2/3 lightspeed, is that ship travelling at 1 1/3 lightspeed relative to her original departure point?

I think that the point is moot though, I cant run that fast.

John Welsford

john welsford
08-20-2017, 08:23 PM
Pat, you actually did a pretty good job of describing the EPR (Einstein-Podolosky-Rosen)experiment, commonly called "Spooky action at a distance."

This is the experiment which offers the best hope of faster-than-light travel, yet still there is no agreement. One of the problems in the experiment is that nothing is actually traveling between the two particles. It's not like one particle emits something which travels a distance and then the other particle absorbs it.

What occurs is the simultaneous resolution of superimposed quantum states. Coordination without communication. One way to think about it is that the two particles, although separate, are still actually the same particle - just as they were at the beginning of the experiment. It just happens to be very, very delocalized.

At best, in the EPR experiment one could say there has been faster-than-light transmission of a quantum state. But one cannot claim to have transmitted anything such as mass or energy over that distance -- and nothing at all traveled from one place to the other.

<hr>Meerkat, the microwave experiment you described is a common source of confusion. The problem, as Ingo points out, is that there are different types of velocity -- but not all transmit real information. In this case, someone has confused phase velocity or group velocity with true velocity.

There are a couple of simple experiments that illustrate the problem. Imagine you are shining a laser pointer on a movie screen from 100 feet away. By making a small motion of your wrist, you can cause the laser dot to move very fast from one side of the screen to the other. Now, if you move that screen very far away (lets say to the moon, or perhaps a light year away), the same small motion of your wrist will result in a much larger motion of the laser dot.

In fact, if that screen were one light-year across, but so far away that you can scan from the left to the right edge with just a flick of your wrist, you'd see that laser dot move a full light year in a fraction of a second -- very much faster than the speed of light!

But you must ask yourself what is really moving? What is the laser dot? It's nothing. The true movement is the light coming out of your pointer, hitting the screen and reflecting back to you.

The second experiment you can observe at the beach. Imagine a steady stream of waves coming into the beach at almost exactly a 90 degree angle. At the edge of the beach is a low wall so that when the wave hits, it sends up a splash of foam.

If the wave hits at exactly a 90 degree angle, the entire wave will hit the wall at once, sending up a uniform splash. If the wave comes in at 45 degree angle, the splash will start when one edge of the wave first hits, and then travel along the wall at sqrt(2) times the speed of the wave.

If the wave comes in at almost 90 degrees, you will see the splash start at one end and travel very, very fast to the other end of the beach.

But again, you have to consider what is actually doing the traveling. The splash is nothing. The only thing that is actually traveling is the wave and that's only moving in one direction, not along the length of the wall.

<hr>Ingo, when you say the speed of light can be higher in a material than in a vacuum, I think you are referring to Negative Index materials or left-handed materials.

These materials are awfully confusing, but do not cause the speed of light to increase. (http://physicsweb.org/articles/news/7/3/12)

I think the best way to describe it is to say that when light enters the material, the end of the signal emerges before the beginning. This means that the end of the signal traveled faster than the start --- not because it traveled faster than the speed of light but because the start of the signal was delayed.

[ 03-12-2006, 10:52 AM: Message edited by: ljb5 ]

Nice explanation here, thanks for that.
Here's another thought, see my previous post which mentioned red and blue shift as a consequence of relative velocity twixt source and point of observation. I was reading a while back that someone had put forth the theory that it may be possible to transmit information instantly by establishing a light beam from source to observer, then moving the source back and forth to moderate the colour shift that the observer would experience.
Any thoughts on that?

John Welsford

sharpiefan
08-20-2017, 09:47 PM
Very true.

They also would bounce off each other -- but that never happens. Photon pass directly through each other and never experience photon-photon scattering.


LHC experiment is first direct evidence of photon-on-photon scattering (LINK) (https://www.sciencenews.org/article/lhc-atlas-photons-interact-physics)

mmd
08-20-2017, 09:59 PM
A fine effort, Jack. Nice pick.

jack grebe
08-21-2017, 02:09 AM
LHC experiment is first direct evidence of photon-on-photon scattering (LINK) (https://www.sciencenews.org/article/lhc-atlas-photons-interact-physics)

I remember doing an experiment in grade school that also brought about the same result......

2 slide projectors with intersecting beams, each turned on independently and adjusted for clarity.

When the projectors were turned on together, both were blurry,

oldcodger
08-21-2017, 03:20 AM
Something interesting that I've not got the math to get my head around, is that the speed of light is a "local constant". That is, light emitted by two different sources, one travelling toward the point of observation, and the other away, arrives at the p.o.observation at the same speed but blue or red shifted accordingly.

That said, imagine, if a spaceship were to accelerate up to say 2/3 lightspeed, rendezvous with an object travelling away from her point of departure at that speed, then accelerate away from that object to a speed relative to that of 2/3 lightspeed, is that ship travelling at 1 1/3 lightspeed relative to her original departure point?

I think that the point is moot though, I cant run that fast.

John Welsford

This is a case where 2 + 2 does not equal 4 or 5 but 3 |:). Using common sense in relativity and quantum theory is a disadvantage.

Relative velocity is governed by the formula V = (v-u)/(1-v*u/c*c) { people use different letters but the equation stays the same}

At low speeds v*u/c*c is so small that 1-v*u/c*c is in effect 1, so V = v-u which is what we experience in every day life.

In your case where you had 2 bodies travelling away from each other at say .6 speed of light (for ease of calculation) you get .6-(-.6) = 1.2c for the top line and 1- .6c*-.6c/c*c. for the bottom line, the minus signs and the Cs cancel leaving 1 +.6*.6 = 1+.36.

Dividing top line by the bottom line 1.2c/1.36 = .882c so below the speed of light.

Or listen to this guy ( ignore most of the blackboard formulae left over from an earlier lecture)

https://www.khanacademy.org/science/physics/special-relativity/einstein-velocity-addition/v/applying-einstein-velocity-addition

webishop14
08-21-2017, 08:05 AM
Jack --

Your experiment in your last post prompts me onto a slightly tangential direction. Have you seen or read anything about Edwin Land's work in color in the early fifties? Still rather mind-blowing.

jack grebe
08-21-2017, 08:17 AM
Jack --

Your experiment in your last post prompts me onto a slightly tangential direction. Have you seen or read anything about Edwin Land's work in color in the early fifties? Still rather mind-blowing.


No I have not

mmd
08-21-2017, 09:11 AM
I remember reading about Land's work on colour when I was studying pro photography in college a very long time ago. I recall it as being very interesting, but I have forgotten most of it in the intervening years. Now that webishop14 has reminded me of it, I may have to dust off the old college books and refresh my memory.

webishop14
08-21-2017, 09:17 AM
IIRC, Scientific American ran several articles in the late fifties or early sixties. Using black and white film, take two pictures (slides) of the same scene. Same point of view, same lighting. Only difference: use a colored filter on one exposure. Project the images -- as you did -- using two projectors to superimpose the images. Put a colored filter over one of the outputs -- and voila! -- a full color reproduction of the original scene. Details are a bit fuzzy in my memory after almost 60 years. But easily googled.

amish rob
08-21-2017, 09:36 AM
Maybe light move like waves, and only the energy moves, eh?

The individual particles would be affected by gravity, etc, but the energy itself would be merely pouring along a conduit.

Oh, I mean, that's how light can travel at the speed of itself.

Peace,
Robert

webishop14
08-21-2017, 09:47 AM
Speed requires time. And time, t = sqrt(m*d/F). Which could be interpreted to mean that time is an artifact of the displacement of mass.

jack grebe
08-21-2017, 10:11 AM
I remember on the old oscilloscope that time was measured, not frequency, where does mass
Play into that?

webishop14
08-21-2017, 10:50 AM
According to my old text Concepts of MASS in Contemporary Physics and Philosophy, by Max Jammer, mass, gravitational mass, that is, works out as m = f/g. Turns out its all a circular definition. Which might explain why the three-body problem cannot be solved.

jack grebe
08-22-2017, 12:20 AM
Ok, so if a blackhole is bending time/space to the point that light
cannot escape, what is the gravity pulling on? Does time have mass?
Space?

Breakaway
08-22-2017, 12:21 AM
Ok, so if a blackhole is bending time/space to the point that light
cannot escape, what is the gravity pulling on? Does time have mass?
Space?

Spacetime is one thing. it is the fourth dimension.

Kevin

jack grebe
08-22-2017, 12:37 AM
Spacetime is one thing. it is the fourth dimension.

Kevin

Ok, I never got deep into physics..... I hated math. I always assume that space/time
We're separate dissecting mediums as illustrated by the graph type representation
Of black holes.

webishop14
08-22-2017, 08:12 AM
Spacetime is one thing. it is the fourth dimension.

Kevin

Well, the first four dimensions. The ones we can sense. We haven't even begun exploring the other seven.

sharpiefan
08-22-2017, 09:23 AM
Well, the first four dimensions. The ones we can sense. We haven't even begun exploring the other seven.

I have a nagging suspicion that, like dark matter & dark energy, "the other seven" were invented to cover the fact that physicists don't know as much as they want us to think they do. They're fudge factors to make the numbers look pretty. They're like Carl Sagan's invisible, incorporeal, floating dragon.



'A fire-breathing dragon lives in my garage.' Suppose (I’m following a group therapy approach by the psychologist Richard Franklin) I seriously make such an assertion to you. Surely you’d want to check it out, see for yourself. There have been innumerable stories of dragons over the centuries, but no real evidence. What an opportunity!

‘Show me,’ you say. I lead you to my garage. You look inside and see a ladder, empty paint cans, an old tricycle - but no dragon.

‘Where’s the dragon?’ you ask.

‘Oh, she’s right here,’ I reply, waving vaguely. ‘I neglected to mention that she’s an invisible dragon.’

You propose spreading flour on the floor of the garage to capture the dragon’s footprints.

‘Good idea,’ I say, ‘but this dragon floats in the air.’

Then you’ll use an infrared sensor to detect the invisible fire.

‘Good idea, but the invisible fire is also heatless.’

You’ll spray-paint the dragon and make her visible.

‘Good idea, except she’s an incorporeal dragon and the paint won’t stick.’

And so on. I counter every physical test you propose with a special explanation of why it won’t work.

Now, what’s the difference between an invisible, incorporeal, floating dragon who spits heatless fire and no dragon at all? If there’s no way to disprove my contention, no conceivable experiment
that would count against it, what does it mean to say that my dragon exists? Your inability to invalidate my hypothesis is not at all the same thing as proving it true. Claims that cannot be tested, assertions immune to disproof are veridically worthless, whatever value they may have in inspiring us or in
exciting our sense of wonder. What I’m asking you to do comes down to believing, in the absence of evidence, on my say-so.

The only thing you’ve really learned from my insistence that there’s a dragon in my garage is that something funny is going on inside my head.


The Demon-Haunted World
Available in many formats at Internet Archive (LINK) (https://archive.org/details/DemonHauntedWorld_carlSagan)

webishop14
08-22-2017, 11:18 AM
I have definitely heard it stated that eleven dimensions were necessary in order to make the math work. Not having vetted their mathematics, I have no opinion. (Please don't assume I'd be capable of vetting their math.)