Info traveling faster than light, and quantum entanglement

[bobtom]

OK, going to ask a question that I sort of know is going to be shot down but at the moment I can't make sense of this.

If I send a machine/robot with a particle that is quantum entangled with another particle that is left on earth. When one particle is blue the other is red. The machine also has an ability to measure whether there is liquid water on a planet around proxima century. So I send it to porxima, let's say at the speed of light, so it takes just over 4 years to get there (it’s irrelevant how fast it gets there).

So my robot arrives at proxima and measures there is liquid water on this planet. I make the particle on my robot red, which we have already decided means that there is liquid. So now we know our particle is blue, the other must be red therefor there must be liquid water on this planet.

Has info traveled faster than light or have we just deduced that there is water on this planet because our particle is blue? Have we quantum entangled the information?

We have deduced it but as long as something hasn’t gone wrong with our machine then we know this information and it has traveled faster than light. Is it because we know it IF our machine hasn’t broken and accidentally made the particle the wrong colour then the information has traveled faster than light. So the full info hasn’t travel-led faster than light because we can’t be 100% certain the machine hasn’t malfuncrtioned and made the particle the wrong colour. Do we truly KNOW it or have we just deduced it.

What happens if I send a million machines and they all take measurements and report back there is water.

What I don't understand is why the information hasn't traveled faster than light?

 

[Doc Al]

I make the particle on my robot red, which we have already decided means that there is liquid. So now we know our particle is blue, the other must be red therefor there must be liquid water on this planet.

You don't get to "make" the particle red. You can observe (measure) the color of the particle and find it to be red (which tells you that a similar measurement on the entangled particle will find it to be blue). No information that you can control has been sent.

 

[bobtom]

So I can't make the particle be in one state or another at all? It has to be observed for it to be in any certain state?

 

[Doc Al]

So I can't make the particle be in one state or another at all? It has to be observed for it to be in any certain state?

Right. You cannot choose the state of the particle. (Until you make the measurement, the particle is in a superposition of states -- an entangled superposition.)

 

[DrChinese]

I make the particle on my robot red...

Just to clarify Doc Al's correct answers: the outcome of any measurement on Earth will be random. You can't transmit information using random signals. You can see the correlation Blue/Red or Red/Blue. But to do that, you need a classical signal channel. So again, no FTL signals.

 

[bobtom]

So if I were to observe a quantum entangled particle to be in one state, is that state just random then? So the particle could end up being observed blue or red and then that decided the state of the other one?

 

[David Byrden]

So the particle could end up being observed blue or red and then that decided the state of the other one?

Ahhh, NOW you get it!

 

[bobtom]

Thanks for the help guys, I was pretty sure there was something basic I was missing. Mucho appreciado.