Imagine a simple circuit. Just a lamp a power supply and a switch connected so that when you throw the switch, the light goes on.
Question: Now imagine this circuit to have the size of the visible universe, with all the 3 components as far away as possible. If you throw the switch when does the light go on?
Question: Now imagine this circuit to have the size of the visible universe, with all the 3 components as far away as possible. If you throw the switch when does the light go on?
Assuming straight copper wires join the 3 components, and ignoring losses and external effects, the lamp should come on about 85 billion years after the switch is flicked. This assumes 85 billion years already passed for the potential to travel from the source to the switch and the other side of the lamp.
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You would think that, because information can't travel faster than the speed of light.
But the electrical potential is everywhere in the circuit, so as soon as the switch is closed the light goes on. The information doesn't need to travel the galaxy, it's already there.
That is incorrect. At rest with switch off, the potential on one side of the switch is "high" (let's call it) and on the other "zero". And both sides of the lamp also "zero". And so the potential of the wire between switch and lamp must come up to high before the lamp comes on.
Simulate your circuit, and look at the voltage on each net / wire. You'll see what I mean. When the switch is off, the potential or voltage is (necessarily) the same on both sides of the lamp. The fact the power source provides the potential isn't relevant.
The electrical 'signal' in a piece of wire runs at somewhat less than the speed of light (we used to estimate about 50% when running big old computers in the 1970s). Even back then this loss of time was significant and timing signals to the other end of the processor were sent out out 'early' so as to arrive at the 'right' time. We were obliged to find 3 oscillscope leads (2 signals and trigger) of the same length to investigate some faults.
So the light at the end of the universe will take an awfully long (infinite?) amount of time to switch on.
Are you also taking into account the continuous expansion of the universe?
So the light at the end of the universe will take an awfully long (infinite?) amount of time to switch on.
Are you also taking into account the continuous expansion of the universe?
This is a 2 wire circuit, joining a voltage source and a lamp.
The switch does not add/substract anything to that, it just opens or closes the circuit.
So to simplify analysis let´s put it just by the voltage source, although as far as timing goes, it can be anywhere along any of both wires.
So with switch OFF there´s 0V voltage difference between both wires, 0V across lamp bulb terminals, full voltage across supply terminals.
Throw switch ON and now you are applying full supply voltage to the pair of wires.
We can also describe such voltage as a *signal* ; the pair of wires as a *transmission line* ... because that´s what both things are, and signal will travel along that transmission line the way we already know.
As mentioned above, somewhat slower than speed of light by a known factor, so longer than 85 Million years which get divided by said factor.
A minor point which does non alter analysis outcome: since you said "3 elements as far as possible from each other" we won´t have an 85 million light years diameter path (if we consider Universe a Sphere) but a longer one, we will position 3 elements on 3 vertices (don´t know the English word) of an equilateral triangle, touching said sphere surface, but simple Trigonometry solves that.
The switch does not add/substract anything to that, it just opens or closes the circuit.
So to simplify analysis let´s put it just by the voltage source, although as far as timing goes, it can be anywhere along any of both wires.
So with switch OFF there´s 0V voltage difference between both wires, 0V across lamp bulb terminals, full voltage across supply terminals.
Throw switch ON and now you are applying full supply voltage to the pair of wires.
We can also describe such voltage as a *signal* ; the pair of wires as a *transmission line* ... because that´s what both things are, and signal will travel along that transmission line the way we already know.
As mentioned above, somewhat slower than speed of light by a known factor, so longer than 85 Million years which get divided by said factor.
A minor point which does non alter analysis outcome: since you said "3 elements as far as possible from each other" we won´t have an 85 million light years diameter path (if we consider Universe a Sphere) but a longer one, we will position 3 elements on 3 vertices (don´t know the English word) of an equilateral triangle, touching said sphere surface, but simple Trigonometry solves that.
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Was the OP seeking knowledge or trying to teach us his own confusion? This type of thread can go either way. Anyway, he has been given the correct answer.
I solved for an equilateral triangle based on the sphere of the visible universe at 93 billion light years across and propagation velocity of a signal in copper wire @ 95% of c.
(93 cos(30)) / 0.95 = 84.77
I prefer the transmission line approach: the wires from the switch to the bulb are 'streched' coils and do have some capacitance qualities. Hence a transmission line and propagation delay from start to finish (indeed simulations will proof).
So, not the quantity of time that will elapse before the universe is enlighted, but a obvious fact that it will take some time but not yet accurately defined before the actors can enter the (ever expanding) stage visible to unveil the 'truth' about their universe.
Until then, I dismiss myself from the final outcome of this hypothetical discussion.
So, not the quantity of time that will elapse before the universe is enlighted, but a obvious fact that it will take some time but not yet accurately defined before the actors can enter the (ever expanding) stage visible to unveil the 'truth' about their universe.
Until then, I dismiss myself from the final outcome of this hypothetical discussion.
Of course it is, but I'm not an astrophysicist, or a very good mathematician, and this is a thought experiment so we can exclude such factors for the purpose of making things simple... Regardless the answer is "a very long time" whether it's 85 billion years or 200 billion years isn't really here nor there
Electricity doesn't flow like water in a hose, as some may think.
Not having the specifics handy right now (you can google it yourself) electricity energy "moves" from molecule to molecule, first "bumping the closest molecule, which then "bumps" the next one, and so forth.
Like a chain reaction down the wire...
Not having the specifics handy right now (you can google it yourself) electricity energy "moves" from molecule to molecule, first "bumping the closest molecule, which then "bumps" the next one, and so forth.
Like a chain reaction down the wire...
I would describe it as a domino effect. But you're right, the concatenation of events would take time!
True enough, still the basic point is that signal travels along a wire at light speed multiplied by a somewhat smaller than 1 factor .
That said factor is 0.95 , 0.85 or even 0.54 is slightly irrelevant, we are comparing 2 hypothesis: "instant ON" pioneered by the OP and "millions of years" by everybody else, based on ... um .... Physics.
Not even need to go into a microanalysis of what happens at sub atomic level; signal transmission , both in vacuum and in conductors has already been studied and settled on for, what? ... over 100 years now?
And to avoid nitpickers beforehand: throwing a switch ON IS sending a signal along it.
In this case a single step one, voltage = supply voltage.
EDIT: as of:
And maybe a preconceived answer which didn´t hold but nothing beyond.
God knows we have had our fair share of trollish baited "seemingly innocent" questions designed to stir the pot, but not here 🙂
That said factor is 0.95 , 0.85 or even 0.54 is slightly irrelevant, we are comparing 2 hypothesis: "instant ON" pioneered by the OP and "millions of years" by everybody else, based on ... um .... Physics.
Not even need to go into a microanalysis of what happens at sub atomic level; signal transmission , both in vacuum and in conductors has already been studied and settled on for, what? ... over 100 years now?
And to avoid nitpickers beforehand: throwing a switch ON IS sending a signal along it.
In this case a single step one, voltage = supply voltage.
EDIT: as of:
in this particular case I don´t suspect a troll at all, just a sincere question.
And maybe a preconceived answer which didn´t hold but nothing beyond.
God knows we have had our fair share of trollish baited "seemingly innocent" questions designed to stir the pot, but not here 🙂
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Since the observer must be stationed at the switch and the switch is positioned as far as possible from the light then the observer will only be able to confirm that the light is on after the light from the bulb has travelled across the universe to the observer located at the switch - hence the calculations above are under estimating the time taken as measured by the observer
Maybe the observer has very long arms and can throw the switch from his position near the lamp 😎
How long does it take for him to stretch out his arm from his position near the lamp to reach the switch?
Hypothetical, of course .
Jan