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[Prez]

The explanation from Brian Greene's "The Fabric of Cosmos" is by far the easiest to understand.

It's all about relativity. The faster you move, the slower time goes by in relation to everything else. If you were to move at almost the speed of light, seconds would pass by for you while millions, even billions of years pass by on earth. At exactly the speed of light, time simply stops. That's why light doesn't age.

Also, Light always moves at 300,000km/second in relation to any object. If you were to move at exactly the speed of light, light would still appear to move 300,000km/second in relation to you.

I hope I got this all correct. It's been more than 2 years since I read that explanation from Greene's book, but I've thought about it a lot.

 

[LCfiner]

Considering that we thought the would was flat a mere 500 years ago, you're probably right.

that’s not true. humans knew the earth was round thousands of years ago.

bad history and geography classes the world over have propagated this silly myth about how everyone thought the earth was flat hundreds of years ago.


I gotta re-read why light speed is the speed limit in the universe but right now, nothing travels faster than it. (although I do hear about quantum entanglement experiments that I barely understand that seem to allow for some atomic properties to travel between a pair of particles faster than light)

edit:

No because that would be implying gravity travels through space like light. It doesn't, it is a persistent effect that is woven into timespace.

gravity travels at the speed of light. it’s not instantaneous.

 

[StuBurns]

Also, Light always moves at 300,000km/second in relation to any object. If you were to move at exactly the speed of light, light would still appear to move 300,000km/second in relation to you.

This is going to be hard to ask, so I'll try my best.

The reason black holes are black is because every massive body has an escape velocity, and with a black hole the escape velocity is actually greater than the speed of light. So we see no light escape.

If you could pass a black hole making up the deficient between the speed of light and the escape velocity of a black hole, would you be able to see into it?

 

[Prez]

This is going to be hard to ask, so I'll try my best.

The reason black holes are black is because every massive body has an escape velocity, and with a black hole the escape velocity is actually greater than the speed of light. So we see no light escape.

If you could pass a black hole making up the deficient between the speed of light and the escape velocity of a black hole, would you be able to see into it?

How the fuck should I know?

Spoiler

sorry, lol

 

[DanteFox]

I like Stephen Hawking's explanation in A Brief History Of Time.

 

[LCfiner]

This is going to be hard to ask, so I'll try my best.

The reason black holes are black is because every massive body has an escape velocity, and with a black hole the escape velocity is actually greater than the speed of light. So we see no light escape.

If you could pass a black hole making up the deficient between the speed of light and the escape velocity of a black hole, would you be able to see into it?

Nope. light will not escape the black hole under any circumstance. it does not matter how slowly or quickly you are travelling next to one. the mass of the object getting sucked in does not matter either as light travels at a constant speed and it cannot escape the black hole. you will not be able to see inside.

 

[ronito]

simple to understand = a few sentences or a paragraph at most

 

[Meus Renaissance]

Isn't that what the Alcubierre drive does?

There was ST episode where they discovered frequent use of the warp drive was damaging the fabric of space. Can't remember the details of the hypothesis, but is it possible excessive use of the Alcubierre drive could be harmful?

 

[StuBurns]

Nope. light will not escape the black hole under any circumstance. it does not matter how slowly or quickly you are travelling next to one. the mass of the object getting sucked in does not matter either as light travels at a constant speed and it cannot escape the black hole. you will not be able to see inside.

Shame, I wouldn't mind a quick look in there. Thanks for the reply

 

[weekend_warrior]

gravity travels at the speed of light. it’s not instantaneous.

Persistent does not equal instantaneous.

Imagine:

You drop a bowling ball onto a trampoline, it creates a crater around it. Then imagine placing a marble around the outer edge of the crater. The marble rolls into the bowling ball. If this was a galaxy the marble wouldn't instantly feel the affects to the bowling ball, nor would it take millions of years for the gravity to reach the marble. It would be reacting to the persistent affect of gravity already there.

 

[mike23]

I agree with the sentiment that it's a bit too soon to start ruling things out. I don't think 100 years of significant scientific progress is enough to start saying what is or isn't absolutely possible. There's so much that we don't know, so saying traveling FTL is absolutely impossible truly is arrogant. Like it only took us 100 years to figure what is and isn't possible. One time's science is another time's magic.

Humans love to bask in our intelligence, but there's really no evidence that we're anywhere near the epitome of real intelligence. Even among humans there are people (with near identical brain size) who are obscenely more intelligent than everyone else. Imagine a being with a brain twice as large or with another million years of natural selection in an environment where intelligence is preferred. They'd look at all our progress and see us as we see chimps.

Oh look, those humans have rocket spaceships. vs. Oh look, those chimps can use a stick to get at ants.

 

[StuBurns]

Persistent does not equal instantaneous.

Imagine:

You drop a bowling ball onto a trampoline, it creates a crater around it. Then imagine placing a marble around the outer edge of the crater. The marble rolls into the bowling ball. If this was a galaxy the marble wouldn't instantly feel the affects to the bowling ball, nor would it take millions of years for the gravity to reach the marble. It would be reacting to the persistent affect of gravity already there.

Google it, everything seems to say you're wrong. Or not really wrong, but are wrong that it's not at the speed of light.

The speed of light is the highest speed of any reaction within the universe, including gravitational waves.

 

[LCfiner]

Persistent does not equal instantaneous.

Imagine:

You drop a bowling ball onto a trampoline, it creates a crater around it. Then imagine placing a marble around the outer edge of the crater. The marble rolls into the bowling ball. If this was a galaxy the marble wouldn't instantly feel the affects to the bowling ball, nor would it take millions of years for the gravity to reach the marble. It would be reacting to the persistent affect of gravity already there.

I have not read anything that suggests gravity propagates at any speed other than the speed of light.

if you have links to research and observations to suggest that gravity waves are either slower or, somehow, faster than light, please link them.

 

[Haly]

I'm getting some contradictory answers but one thing seems consistent.

Gravity must propagate at some speed, otherwise it violates causality, which holds up the universe blah blah blah.

Let's get one thing straight here, when I say "speed of gravity" I mean how long it takes for Object B to respond to any changes in the gravitational field of Object A. For example, if B is orbiting A, and suddenly half of A disappears, would B immediately begin to spiral away from A or would it take sometime before B goes "oh, A is smaller now" and start spiraling away.

In your example, the marble is placed into the preexisting vector field of the bowling ball/galaxy. Of course it responds immediately.

 

[ethic]

So as you move through space a bit more quickly, you find yourself moving through time a bit more slowly.

I don't understand the connection between those...

 

[mike23]

I think I understand what he's saying, maybe.

Changes in gravity propagate at the speed of light. However, gravity "fields" already exist in space. There aren't points of origin for gravity, but a field that is merged with the universe. Sort of like a magnetic field around a ferro-magnet. The field exists all around the magnet at all times. The field propagates at the speed of light if the magnet gets weaker/stronger or it moves, but a piece of metal stuck in the field is instantly affected by the magnetic field since the magnetism exists all in that area.

 

[weekend_warrior]

I think I understand what he's saying, maybe.

Changes in gravity propagate at the speed of light. However, gravity "fields" already exist in space. There aren't points of origin for gravity, but a field that is merged with the universe. Sort of like a magnetic field around a ferro-magnet. The field exists all around the magnet at all times. The field propagates at the speed of light if the magnet gets weaker/stronger or it moves, but a piece of metal stuck in the field is instantly affected by the magnetic field since the magnetism exists all in that area.

this.

 

[Scrow]

Even if FTL is not possible why is it of any concern of ours? It'll never happen in our lifetimes even if it is possible.

what a completely non-sensical statement on all levels.

 

[StuBurns]

this.

This was the question:

How fast does the effect of gravity go?

So that's not what you were saying surely.

 

[mike23]

I don't understand the connection between those...

Everything is currently moving at c. I don't know why it is, but it is.

Normally, 99.9999+% of your velocity is forward in time. A fraction is moving east or west, north or south, forward or backward.

So (speed moving through time) + (speed east/west) + (speed north/south) + (speed forward/backward) = the speed of light at all times. A change in one must be balanced by a change in another.

 

[mike23]

This was the question:

How fast does the effect of gravity go?

So that's not what you were saying surely.

The effect of gravity is instant I think. If you plop into existence, you are effected by the gravitational equilibrium that has formed in the spot where you appear instantaneously. Your effect on gravity will then propagate through the universe at the speed of light as it alters the equilibrium.

edit: His analogy with the trampoline was good. The gravitational field would be the hill created when the bowling ball pushes down on the trampoline. Anything put on the trampoline is instantly affected by the hill and the marble will roll. When the bowling ball is placed on the trampoline, the change in the trampoline's shape is propagated at the speed of light towards the edges, but once it's changed, the effects are persistent.

 

[LCfiner]

The effect of gravity is instant I think. If you plop into existence, you are effected by the gravitational equilibrium that has formed in the spot where you appear instantaneously. Your effect on gravity will then propagate through the universe at the speed of light as it alters the equilibrium.

nvm

 

[Haly]

It comes down to how you read that question.

I read it as a crude way of saying "how fast does gravity propagate", since the alternative question is kind of pointless and doesn't really follow the flow of the thread.

 

[StuBurns]

The effect of gravity is instant I think. If you plop into existence, you are effected by the gravitational equilibrium that has formed in the spot where you appear instantaneously. Your effect on gravity will then propagate through the universe at the speed of light as it alters the equilibrium.

Do things ever plop into existence? I'm pretty sure that's not what the question was asking.

 

[ThoseDeafMutes]

I like:



Simple and straight to the point.

More explanation is required because then people say "but what if we found some other way to break the 'light barrier'?"

This is a somewhat confusing explanation for why FTL implies time travel, but I think it's not too bad if you really think about it.

 

[weekend_warrior]

Do things ever plop into existence? I'm pretty sure that's not what the question was asking.

Exactly, objects with mass doesn't spontaneously appear, thus creating a need for gravity to propagate through space. It's a persistent force, changing and moving, but only in response to the object creating it. Thats why asking what the speed of gravity is doesn't make sense, since the only way to measure it is by measuring the particles it affects, which we know can't exceed the speed of light.

 

[Tornado Condor]

I took a physics class and it deal with relativity. Oh god, that shit was mega complicated. I'm so glad i'm over it =(

 

[Korey]

So, has anyone explained why LIGHT is the fastest thing in the universe yet? What's so special about light?

 

[Tornado Condor]

So, has anyone explained why LIGHT is the fastest thing in the universe yet? What's so special about light?

Because photons have no mass, maybe? Neutrinos come close!

 

[ChoklitReign]

I've read Physics of the Impossible and there are loopholes that allow real FTL travel, except the energy requirements are far beyond our modern technology. I trust Michiou Kaku over Reddit.

 

[ThoseDeafMutes]

So, has anyone explained why LIGHT is the fastest thing in the universe yet? What's so special about light?

The constant C is the maximum speed at which information may propagate. Photons actually go the tiniest bit below that speed, depending on the diffraction of the medium they are in (and there are no perfect vacuums). As for why Photons go as fast as they do, it's because they are massless.

I've read Physics of the Impossible and there are loopholes that allow real FTL travel, except the energy requirements are far beyond our modern technology. I trust Michiou Kaku over Reddit.

I would trust 4chan over Michiou Kaku.

 

[strata8]

So, has anyone explained why LIGHT is the fastest thing in the universe yet? What's so special about light?

I think esc explained it best:

Massless particles travel the speed of light. Photons, which make up light, are one of those particles, but there are others. These massless particles are the fastest "things" in the universe because they move through spacetime with a velocity that is as fast as the universe will allow; they go the speed limit of the universe. There is nothing that can travel faster in a universe in which relativity applies. The universe itself has set the limits.

 

[LCfiner]

So, has anyone explained why LIGHT is the fastest thing in the universe yet? What's so special about light?

Nothing, really. It's not just light. It's the fastest any process can propogate in the galaxy.

And, I'm pretty sure this is mathematically proven, but anything that is literally weightless must be traveling at this maximum speed. It's the inverse of how any mass would theoretically become infinite of travelling at the speed of light.

So light and gravity are both without mass, so they travel at this universal speed limit.

 

[Lost Fragment]

I've read Physics of the Impossible and there are loopholes that allow real FTL travel, except the energy requirements are far beyond our modern technology. I trust Michiou Kaku over Reddit.

I think those loopholes allow you to move faster than light in a practical sense, but not a technical one.

 

[SoulPlaya]

To move requires energy, and the more mass you have, the more energy needed to make you go a certain speed (relative to something with less mass). Photons, which are massless, require the least amount of energy to go a certain speed (in this case, c). Why that specific number? Who knows?

Did I get it right? I'm getting the math of it, I just want to understand it qualitatively. BTW, E=mc^2 makes a lot more sense with Lorentz factor included in it.

 

[StuBurns]

Exactly, objects with mass doesn't spontaneously appear, thus creating a need for gravity to propagate through space. It's a persistent force, changing and moving, but only in response to the object creating it. Thats why asking what the speed of gravity is doesn't make sense, since the only way to measure it is by measuring the particles it affects, which we know can't exceed the speed of light.

But that's not same thing, now you're saying we can't measure it's speed. You said it is instant. You certainly can't measure that either.

 

[Tornado Condor]

To move requires energy, and the more mass you have, the more energy needed to make you go a certain speed (relative to something with less mass). Photons, which are massless, require the least amount of energy to go a certain speed (in this case, c). Why that specific number? Who knows?

Did I get it right? .

yesh

 

[ChoklitReign]

I think those loopholes allow you to move faster than light in a practical sense, but not a technical one.

What's the distinction? How are wormholes and warp drives practical rather than technical?

 

[ThoseDeafMutes]

What's the distinction? How are wormholes and warp drives practical rather than technical?

They are "practical FTL" because it allows you to beat light in a race to a point in space. They are not "technical FTL" because nothing actually goes faster than light through space. Rather, the fabric of space does shifting around to make your trip shorter.

They're still violating causality, though.

 

[Raistlin]

 

[Feep]

To the above poster: there is no such thing as a perfectly rigid body. Compressive waves would travel down the stick, at no faster than the speed of light.

 

[ThoseDeafMutes]

To the above poster: there is no such thing as a perfectly rigid body. Compressive waves would travel down the stick, at no faster than the speed of light.

Wouldn't it be speed of sound in the medium?

 

[Trent Strong]

No one has explained why massless particles can't travel faster than the speed of light.

 

[strata8]

No one has explained why massless particles can't travel faster than the speed of light.

As far as I can tell from the thread, they just can't. It's a rule of the universe. I honestly don't think there's much point trying to find a reason for it because there isn't one.

 

[The Technomancer]

The intuitive explanation that I've always gone with is a car driving north that must always drive at 100mph. If it decides to go northwest instead then some of that speed is diverted, its just basic vector summation. Only now make north and west space and time. We are always moving through spacetime at the speed of light. When we speed up in space, we slow down in time.

EDIT: Should have read the OP
They use almost the exact same example

And I'm pretty sure that light itself moves at lightspeed because it also is completely timeless. A photon only experiences one "instant"

They are "practical FTL" because it allows you to beat light in a race to a point in space. They are not "technical FTL" because nothing actually goes faster than light through space. Rather, the fabric of space does shifting around to make your trip shorter.

They're still violating causality, though.

Yeah, causality is the real problem.

 

[LaserBuddha]

 

[ThoseDeafMutes]

No one has explained why massless particles can't travel faster than the speed of light.

What are you looking for here? Information cannot exceed C. Ergo, it's the speed limit for anything that can exert causal influence. If you're just doing some "Why why why" stuff, you can stop now because physics will never satisfy you. It can tell you how things are, never why they are.

 

[davepoobond]

you dont need to go faster than light when you can travel more efficiently than light.

boom.

 

[Freshmaker]

simple to understand = a few sentences or a paragraph at most

Wierd. I thought TLDR was forbidden for some reason.

This still isn't that difficult of a concept. (This'll be extra funny if I got it wrong, but here goes.)

Time moves you at a certain rate into the future. When you accelerate, that rate of speed just dovetails into the time gradient so you can never move faster than the passage of time allows within the universal fabric.

 

[The Technomancer]

I read a sci-fi book once in which a machine race dedicated millions of years to placing a perfectly opaque dust cloud between our galaxy and Andromeda, so that then they could open a wormhole and not violate causality. It was....interesting.