RE: Puzzling thing about Speed of Light/Speed of Causality
August 24, 2018 at 9:28 am
(This post was last modified: August 24, 2018 at 10:45 am by Anomalocaris.)
Think of it this way. When you push on a stick, what is happening at a microscopic level the atoms in our hand begins to encroach on the molecules at the end of the stick. The electron cloud around your atoms begin to electromagnetically repell the electron cloud in the atoms of the molecule at the end of this stick. This repulsion travels at speed of light. So when your hand start pushing, it takes a small amount of time before end end of the stick even “knows”. Hence speed of light information travel.
Once the first atoms in the top of the rod sense the encroachment of your hand atoms, it start to move out of the way in response to electromagnetic repulsion. But they were held in place in the rod by electromagnetic forces with other atoms in the rod. So information travels from one atom to another at speed of light and cause them all progressively become “aware” and move. But it takes time not only for the first indication of movement of some atoms to travel to others for the others to move, the atoms and molecules are held in stable configurations that once disturbed takes more time to settle back down, so it takes more time than how long light would take to go from one molecule to another for the full effect of pushing one one side of the molecule to travel to the molecule on the other side.
Hence even though information travels from atom to atom st speed of light, deformation takes much longer to travel from molecule to molecule.
So this is why if you push on a stick, the other end doesn’t feel “ pushed” until long after information had time to travel at speed of light from one end of the stick to the other.
Let’s say you push a rigid metal stick about 90 million miles long going from the earth to the sun, pushing on an/off switch at the surface of the sun. Typical rate of propogation of compression in metal is 2-3 miles per second. So it will take 30 million seconds, or roughly 1 year, before the other end of the stick feels the push.
Add another curve ball to assessing how long it will take for you to notice the sun went out after you pushed on the stick connected to the sun’s off switch. What happens when you turn off the sun? The sun derive all of its output from hydrogen to helium fusion at its core. Let’s say the switch is wired to the core and electric signal travels from the switch to the core. That will take about 1.5 seconds. Let’s say the core turns off (some how) instantly. There is reason to believe turning off the hydrogen-helium fusion reaction will simply initiate higher order fution reaction from helium upwards, but we’ll ignore that. Instantly off means the core will immediately stop putting out more energy. The sun goes dark, right? No.
First, the sun’s surface is incandescently hot, and the sun won’t stop shinning until the surface cools. How long will that take? Well, it won’t even start to cool, or even begin to show the first minute amount of dimmingand reddening, for 3 million years. Why, because when energy is generated at the core in the form of high energy photons, these photons (mostly) don’t just zip out at speed of light taking their energy with them. They instead bounce from atom to atom inside the sun, getting reabsorbed and reradiated from atom to atom. It takes 3 million years for the photons generated the instance before you turned off the core, to actually make its way to the surface of the sun.
So if you poke the off switch of the sun with a stick from the earth. It will take a year before the switch actually move. 1.5 seconds for the off signal to get to the core, 3 million years before the effect of the extinction of the sun’s core becomes noticeable at the suns surface, and 8 more minutes before the very first faintest hint of the effect is noticeable on earth. In this time you died, Jesus failed to come again, humans went extinct, anthropogenic global warming peaked and subsided, new ice ages came and went roughly a dozen time, Himalayas got a few hundred feet taller, Appalachians got a a few hundred feet lower, Pacifica moved north along San Andreas fault to block the golden gate out of San Francisco Bay, and finally cockroaches gazed up in insect wonder at a sun that seems just infinitesimally dimmer and redder, and smaller.
Once the first atoms in the top of the rod sense the encroachment of your hand atoms, it start to move out of the way in response to electromagnetic repulsion. But they were held in place in the rod by electromagnetic forces with other atoms in the rod. So information travels from one atom to another at speed of light and cause them all progressively become “aware” and move. But it takes time not only for the first indication of movement of some atoms to travel to others for the others to move, the atoms and molecules are held in stable configurations that once disturbed takes more time to settle back down, so it takes more time than how long light would take to go from one molecule to another for the full effect of pushing one one side of the molecule to travel to the molecule on the other side.
Hence even though information travels from atom to atom st speed of light, deformation takes much longer to travel from molecule to molecule.
So this is why if you push on a stick, the other end doesn’t feel “ pushed” until long after information had time to travel at speed of light from one end of the stick to the other.
Let’s say you push a rigid metal stick about 90 million miles long going from the earth to the sun, pushing on an/off switch at the surface of the sun. Typical rate of propogation of compression in metal is 2-3 miles per second. So it will take 30 million seconds, or roughly 1 year, before the other end of the stick feels the push.
Add another curve ball to assessing how long it will take for you to notice the sun went out after you pushed on the stick connected to the sun’s off switch. What happens when you turn off the sun? The sun derive all of its output from hydrogen to helium fusion at its core. Let’s say the switch is wired to the core and electric signal travels from the switch to the core. That will take about 1.5 seconds. Let’s say the core turns off (some how) instantly. There is reason to believe turning off the hydrogen-helium fusion reaction will simply initiate higher order fution reaction from helium upwards, but we’ll ignore that. Instantly off means the core will immediately stop putting out more energy. The sun goes dark, right? No.
First, the sun’s surface is incandescently hot, and the sun won’t stop shinning until the surface cools. How long will that take? Well, it won’t even start to cool, or even begin to show the first minute amount of dimmingand reddening, for 3 million years. Why, because when energy is generated at the core in the form of high energy photons, these photons (mostly) don’t just zip out at speed of light taking their energy with them. They instead bounce from atom to atom inside the sun, getting reabsorbed and reradiated from atom to atom. It takes 3 million years for the photons generated the instance before you turned off the core, to actually make its way to the surface of the sun.
So if you poke the off switch of the sun with a stick from the earth. It will take a year before the switch actually move. 1.5 seconds for the off signal to get to the core, 3 million years before the effect of the extinction of the sun’s core becomes noticeable at the suns surface, and 8 more minutes before the very first faintest hint of the effect is noticeable on earth. In this time you died, Jesus failed to come again, humans went extinct, anthropogenic global warming peaked and subsided, new ice ages came and went roughly a dozen time, Himalayas got a few hundred feet taller, Appalachians got a a few hundred feet lower, Pacifica moved north along San Andreas fault to block the golden gate out of San Francisco Bay, and finally cockroaches gazed up in insect wonder at a sun that seems just infinitesimally dimmer and redder, and smaller.
