There's no such thing. The speed of light is an absolute limit. There's no such thing as time travel, either.

That said, even ordinary light from another star is from the past. If it's 4 light years away it's for years in the past. If it's 100 million light years away it's 100 million years in the past. (Actually, since the universe is expanding, the light we see now is from when the star was 100 million light years away, 100 million years ago -- but at present it would be much farther than that.)

What's not possible is for the light to arrive here any faster than the speed of light, so that we see what's happening now, or more recently than the number of light years between us and that star when the light starts traveling towards us.

Sending information faster than light, would create a situation in which causality could be broken.

But these are very particular words that mean very particular things.

Is a signal information? Only if it passes novel information. Entanglement does not.

Not saying that it exist or will ever exist, but if there was a type of signal that could do it, what would happen?

Just a signal 1 bit signal

A 1 bit signal cannot posses information. You'd require a minimum of 2 bits. 1 bit is just a straight line, no breaks.

You need at least two states, on and off. 1 and 0. Line and Gap. So a minimum of two bits.

Entanglement doersn't pass new information. It only passes information that's embedded into the system at the time of interaction, even if it's unknown.

It's like a quarter. You cannot tell if you will flip heads or tails. But the moment you do, you instantly know what you didn't flip.

Nothing new is created, no new information.

i think the theoretical answer is YES. We also have physicists who firmly believe that time travel is not just possible, but is in fact now a matter of engineering. Keep a skeptical eye on the nay-sayers. Keep an optimistic eye on those who are trying. At 14, the future is yours. Take it and run!

That's completely not true. There are hypotheses about traveling faster than light and sending signals instantaneously that conform with the laws of physics as we know them, we just don't have the technology to confirm these hypotheses and most likely won't for a very long time. You're also wrong about time travel. Technically speaking, you're time traveling at relativistic speeds due to the effects of time dilation. If you're traveling fast enough, you're time traveling simply because you're experiencing time exponentially slower than people on earth. If you're going to talk in absolutes, I'd encourage you to at least read about what you're going to be talking about first.

Well, since it's an imaginary signal, you can invent what happens.

With our current understanding of physics, such a thing is literally impossible.

But as a thought experiment, let's say some alien civilization has figured out how to send a signal faster than the speed of light. What would that look like to us? I think it would appear as though a signal blinked into existence, with no discernable origin point. Depending on just how much faster they could send the signal, and how far it travelled, it would probably look like it appeared ahead of an observable planet, like where the planet will eventually end up many years in the future.

Oohhhh can we make the signal like a greenish color!?

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Yeah. We can even make blue rats!

1 bit is information. 1 bit, by definition, has two states. For example, the presence or absence of a photon can convey the answer to yes/no questions.

If those aliens sent a light speed signal, they would have to wait 4 years to watch us recieve it in the "past". If the signal were faster than light, let's say instantaneous, they would simply see us recieve the message immediately rather than having to wait the 4 year travel time. So I think the answer is no, the message would not travel back in time

Edit: I forgot about the travel time for light from earth to the telescope. The instant message would be viewed arriving in the aliens 4 year old archived footage but still never traveled back in time. It does break causality though

Your point on time and relativity is a good one. But that should not be called time travel. People colloquially use "time travel" to denote an event that breaks causality. You are probably thinking about nonlocality and entanglement. Those do not transfer information or material in a superluminal manner.

I appreciate your distinction between hypothesis and theory. For at least the sake of our current societal ills, a hypothesis should not be taken as a truth until it becomes a scientifically accepted theory.

>That's completely not true.

It's not true nor false. You can't conclude one until practical tests have been made.

1 bit is a single register of representation. You can have a million 0s, or a million 1s, but you cannot combine them in any way.

That's just a point, incapable of possessing information.

1-bit can never be information. Information is defined as the change of states. Not a state itself, and a 1-bit cannot change.

0000000000000000000000000

has no meaning.

111111111111111111111111111111111111

has no meaning.

00 = 0

01 = 1

That's information.

edit: Hey dumdums.... I get this is space and not philosophy of computation. But it's not a hard concept to grasp.

If you've got a single light switch. I can represent it as on or off. But by itself, it cannot represent information. On and Off is not information, it's data.

It's only a combination of ons and offs that qualify. And the moment you introduce something like iteration. Flipping the light switch on and off over time?

You introduce a new register. A new bit. It's no longer 1d data. Now it's 1d data over time. This is two dimensional. 1 bit of data, 1 bit of iteration. 2d. 2 bit, minimum for information passing.

So far as we know, nothing can travel faster than the speed of light. However, a relatively new discovery/concept is called "Quantum Entanglement" in which two or more particles can become connected seemingly regardless of the space between them. In such a case, information could theoretically be transmitted instantaneously

The statement "there is no such thing" is unequivocally false whether or not you agree with what I said in the rest of my comment. There is such a thing, look up the Alcubierre Drive hypothesis.

Yup. That's why it's also called the speed of information . When you look at the night sky, you are looking into a mosaic of past events that happened anywhere from 4 years ago to millions of years ago. Or at least looking at extrasolar stuff. Even sunlight here on earth is 8 minutes old. :-)

You cant exceed the speed of light. Even if you have near zero mass, the amount of energy required to get close to the speed of light goes to infinite.

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What about the Alcubierre Warp Drive?

Anything, be it a physical ship or an electromagnetic signal - radio, arriving faster than light would break causality, as it would be travelling back in time.

Someone that explains this quite well is Prof David Kipping. Watch this video: https://youtu.be/an0M-wcHw5A

It took me a couple of tries to understand the setup of the charts, but after that, it is obvious there would be a problem. Give it a try. You won't be dissapointed.

I was attempting to keep it less technical because of the nature of the OP's question. I was never arguing that causality breaking time travel is possible. I was just refuting the other commentors absolute statements that there is no such thing. Maybe I had to be creative with my meaning when I say time travel but it's nothing my physics professor wouldn't have done.

A bit, by definition, is the possibility of a 0 or a 1.

Now, the problemHehe is you're sending a 0 or 1 with no context.

>It's not true nor false. You can't conclude one until practical tests have been made.

The hypothesis exists therefore there are scientists who at least believe in the possibility that FTL travel is possible. It's also not scientifically impossible, the laws of physics don't forbid it as such. The reason I brought up the Alcubierre Warp Drive is because the person I was commenting to originally made an absolute statement that was wrong. There is a hypothesis therefore it is a thing that exists even if it's not practical theory yet.

Information is not "defined as the change of states." That's simply not true.

Maybe that's what you understand it as, but it's not a standard scientific definition in any field.

>i think the theoretical answer is YES. We also have physicists who firmly believe that time travel is not just possible, but is in fact now a matter of engineering. Keep a skeptical eye on the nay-sayers. Keep an optimistic eye on those who are trying. At 14, the future is yours. Take it and run!

I prefer to keep a skeptical eye on those who are trying as well as an optimistic eye on those who say nay.

A bit, is a storage space for a representation. By the nature of dimensions, a single dimension, be it of physical space or data can never represent change. It's an isolated spot. In order to represent change (information) you have to have a second dimension. An x, and a y.

2-bits is the minimum state for information.

Quantum entanglement does not allow for the transmission of information, according to all experiments we've run.

Information theory? I don't know about you, but that's the one I'd go to if I were looking first.

If you have two atoms in quantum entanglement, and you change the spin of one atom, the other atom will change it's spin to be opposite. Isn't this the essence of transmitting information?

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That is not how it's defined in information theory.

>In information theory, the information content, self-information, surprisal, or Shannon information is a basic quantity derived from the probability of a particular event occurring from a random variable.

That's the definition. Want me to show you where the change is a required part of it?

You would remove it right when I open the thread

It would be if it were true. It's not. That's not what entanglement means. If you change the spin of one, nothing will happen to the other. Changing spin breaks entanglement.

Change is not a requirement of that. Are you under the impression that "event" means "change"?

Ok, you've won

>The hypothesis exists therefore there are scientists who at least believe in the possibility that FTL travel is possible

I've always wondered how FTL would help outside of the local group with an expanding universe.

>Derive - base a concept on a logical extension or modification of (another concept).

In order to derive you must alter the original data. It must change. That is the fundamental aspect of information.

It can change. If it cannot change, it's just data. Not information.

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You could in theory travel to other stars in our star cluster and explore or even live there if you could find a habitable enough planet. That's so far in the future that it really has no practical application other than as an aspiration and inspiration for those doing the work required to eventual get there. There is the other problem of even at twice the speed of light it would still take 2 years to reach Alpha Centauri.

Wouldn't it appear to travel backwards? The signal appears out of nowhere as it is received and slowly traces backwards to its origin

Information transfer is bound by the speed of light. There is no theoretical possibility of going faster. Your experience of a light beam is going to be the same regardless of it’s speed. You will see it when it strikes your eye.

Time travel can only occur relativistically. The faster a mass moves, the slower time elapses for it.

I mean like, that's localized to the Milky Way and the local group. For extra local group travel, it'd basically be impossible.

I didn't realize you were referring to that kind of scale. I can't imagine it would mean much seeing as the outer edges of the universe are already expanding away from us faster than light

What an awesome and insightful question.

Yes, and no.

Let's make a few assumptions. First. Let's assume that both planets are aware of each other and have tech's assumed at each other. Second let's assume that the communication is instantaneous to take out the math issues. Third, only one planet can transmit the messages but the other can recurve them. Finally, assume I'm a random stranger on the Internet and I don't have a PhD in physics.

Both planets are looking at each other and they are seeing photons that bounced off the other planet 4 years in the past. (i.e. they are 4 light years apart) If one planet transmits this instantaneous signal the planet that received the signal will see it as coming from the future because it was transmitted 4 years before the images they are recording on their telescope. So, if they could see the transmitter being built they might see it still under construction for four years after they get the first transmissions.

To the planet transmitting the signal they would get feedback via light speed communications or actual light images in only 4 years rather than the anticipated 8 with communications limited by the speed of light. I think this would look like time dilation rather than time travel to the planet transmitting.

It is not dissimilar to shooting something at long range. If you are the shooter you hear the gun fire and then see the target get hit. If you are standing near the target you see the target react to getting hit long before you hear the gun shot. So, which order you perceive things happening depends on where you are. Of course we are used to the difference in asked between sounds and light so it seems natural but it takes a bit more to shift ourc thinking you you're question

If you change a q-bit its pair also changes instantly no matter where it is in the universe. How does it know? That's information being exchanged faster than the speed of light. Particle physics and quantum mechanics have rules we don't know or understand yet.

Yeah. The fantasy of leaving the local group is basically not realistic and by the time we do learn to do so most of the observable universe will be concentrated almost solely on the edges of the Virgo cluster around Laniakea.

Interesting I always thought it was true! Do you mind providing a source?

No, information can not theoretically be transmitted instantaneously with quantum entanglement.

I don’t think you understand QE.

Say I entangle 2 particles and send particle 2 an arbitrarily far distance away. Particle 1 is the one I measure, and I find out it’s spinning clockwise. I now instantly know that particle 2 is spinning counterclockwise. Until the person with particle 2 measures it they do not know it is spinning counterclockwise.

No information is transmitted, the interesting thing is being able to measure a particle that is not local to me.

If you were able to measure the particle AND alert your companion what the spin was instantly then you would have FTL information transfer.

This supposes that the signal must be “sent.”

Orson Scott Card in Ender’s Game came up with an Ansible which worked via two entangled particles - you could spin one and the other would spin the same no matter how far away it was.

This probably isn’t actually possible, but I think in our hypotheticals it’s fair to consider a form of communication in which the information doesn’t travel faster than light, because it doesn’t travel at all, it simply exists at both ends.

I actually thought about mentioning this, since it's the same exact sci-fi technology they use in the Mass Effect game series to explain instantaneous communication across the galaxy. It's an interesting idea, but I just dismissed it as impossible sci-fi magic. But, who knows? Maybe one day it could be the basis for some real world technology.