Why was the speed of light even considered to be infinite?

[FallenApple]

Wouldn't the first thought be that we would be burned to a crisp if we where hit with all the light(in our path) across the span of the entire universe simultaneously? It seems there could be paradoxes even before the advent of relativity.

Or maybe it was shown mathematically that the energy that reaches us is finite using arguments with falling off of heat across greater distances from the source.( i.e inverse proportionality to surface area.)

 

[DrStupid]

Wouldn't the first thought be that we would be burned to a crisp if we where hit with all the light(in our path) across the span of the entire universe simultaneously? It seems there could be paradoxes even before the advent of relativity.

That's the Olbers' paradox.

 

[CWatters]

Wouldn't the first thought be that we would be burned to a crisp if we where hit with all the light(in our path) across the span of the entire universe simultaneously?

I don't understand what you mean by "all the light (in our path)" but..

Lets say photons of light leave stars at a certain rate. Changing the speed of light would change how long it takes for them to get to us not the rate at which they leave/arrive.

The speed of light was proved to be finite in 1676.
https://en.wikipedia.org/wiki/Rømer's_determination_of_the_speed_of_light

How much was known about stars back then? In the early 1700's Herschel thought that the sun was cool and habitable.

 

[CWatters]

That's the Olbers' paradox.

That was 100 years after the speed of light was shown to be finite.

 

[DrStupid]

That was 100 years after the speed of light was shown to be finite.

That doesn't matter because the paradox is not limited to infinite speed of light.

 

[CWatters]

Agreed. All I meant was Olbers' paradox couldn't be "the first thought" mentioned by the OP because it wouldn't even be proposed for 100 years after the speed of light was known.

 

[DrStupid]

All I meant was Olbers' paradox couldn't be "the first thought" mentioned by the OP because it wouldn't even be proposed for 100 years after the speed of light was known.

If Olbers' paradox would have been proposed by somebody else 100 years before, nothing would change (except that it would be called somebody else's paradox). A finit speed of light still wouldn't solve it.

 

[FallenApple]

I don't understand what you mean by "all the light (in our path)" but..

Lets say photons of light leave stars at a certain rate. Changing the speed of light would change how long it takes for them to get to us not the rate at which they leave/arrive.

The speed of light was proved to be finite in 1676.
https://en.wikipedia.org/wiki/Rømer's_determination_of_the_speed_of_light

How much was known about stars back then? In the early 1700's Herschel thought that the sun was cool and habitable.

"In the path", I'm referring to if light were just shooting out of a star, a bunch of it wouldn't reach us. For example, the light from the other side of the sun doesn't reach us.

But if you imagine the universe as being very large, composed of a lattice of grid points of a bunch of stars,(each grid in space could contain a star) it is conceivable that even if there is a finite rate that every star produces light at, the stars could be arranged so that an incredible about of light would pile up upon us. For example, star1 emits at rate 1. Star 2 emits at rate 2, just slightly off of rate1(slightly out of sync), star 3, rate3... and so on. Further, assume that star 1, star2, ...star n.. are sequentially further away from Earth monotonically.

We can see that much more light would hit us, with much more intensity. If rate1, rate2, rate3... are extremely close such that it is almost continuous, then there could be an indefintely large(depending on arrangement of the lattice of stars) amount of light that converges in on us at an instant.

 

[DrStupid]

We can see that much more light would hit us, with much more intensity. If rate1, rate2, rate3... are extremely close such that it is almost continuous, then there could be an indefintely large(depending on arrangement of the lattice of stars) amount of light that converges in on us at an instant.

That would also happen with a limited speed of light.

 

[Vanadium 50]

One car per day leaves Boston for Providence at 30 mph. How many cars per day arrive in Providence?
One car per day leaves Boston for Providence at 45 mph. How many cars per day arrive in Providence?
One car per day leaves Boston for Providence at 60 mph. How many cars per day arrive in Providence?

 

[FallenApple]

That would also happen with a limited speed of light.

I see your point. Perhaps, I should have included red shifting due to expansion of space.

If the universe is infinite, then it's possible that we can burn up even if the speed of light is finite, since light from infinitely far way could hit us. But dark energy saves us.

 

[DrStupid]

I see your point. Perhaps, I should have included red shifting due to expansion of space.

Nobody was thinking about an expanding universe when the speed of light has been considered to be infinite.

A better question would be why the universe has been considered to be static.

 

[FallenApple]

One car per day leaves Boston for Providence at 30 mph. How many cars per day arrive in Providence?
One car per day leaves Boston for Providence at 45 mph. How many cars per day arrive in Providence?
One car per day leaves Boston for Providence at 60 mph. How many cars per day arrive in Providence?

How about an infinite amount of cars leave for Providence from every direction. With each direction of approach coorespponding to a to a rate that is unsynchronized, not necessarily different. How many cars would arrive in Providence? Infinite.

 

[FallenApple]

Nobody was thinking about an expanding universe when the speed of light has been considered to be infinite.

A better question would be why the universe has been considered to be static.

Yeah that is true, thinking about an expanding universe may be too premature at that point.

Well, thinking again about the issue, I think I meant to say that the rates are unsynchronized, but doesn't have to be different, though it could be.

Surround a point in space with an imaginary 2d sphere. I

f every point on the surface shines inwards towards the center at different times, then there would be a continuous beam hitting the center since every moment in time corresponds to a light particle launched towards the center under two conditions. 1)Infinite universe in age and size. 2) Infinite speed of light with a very large universe.

1)the universe is infinite in age and size, assuming stars always existed, then every point on that sphere would truly map towards the center, even if light was finite in speed because just by chance out of infinite possibilities of arraignment of infinite stars.

2) But if light is infinite in speed, then I don't think an infinitely old universe is required, just one infinite in size or very large, then the same would happen. All points on that 2d sphere would converge towards the center. In fact, if the universe here is infinite in size, then since light here is also infinite in speed, then you would have infinite overlapping particles of light hitting the center of the sphere at the same time.

In modern parlance, this would reduce everything to a kugelblitz black hole, leaving the universe in a state of maximum and constant entropy, which we know is not true.

But back then, they should still suspect that points in space everywhere would burn up, since light is bright and in general, bright things have heat, fire is hot, sun is hot, molten metal shines and is hot etc, so it is not unreasonable to assume that light itself could be associated with thermal properties.

 

[russ_watters]

How about an infinite amount of cars leave for Providence from every direction.

That isn't how light works though, regardless of its speed.

 

[DrStupid]

2) But if light is infinite in speed, then I don't think an infinitely old universe is required, just one infinite in size or very large, then the same would happen.

And why should that rule out the infinite speed of light and not the infinite homogeneous distribution of stars?

 

[FallenApple]

That isn't how light works though, regardless of its speed.

My argument is combinatoric. Not about the actual process of generating light per se.

If there are a large enough amount of stars, many of those stars shine 360 all around. Then some is aimed at us. So if the universe is infinite, which Newton thought at the time, then I could argue that there are infinite stars, each one shining in every directions. Therefore, each one is aiming light directly at us. And infinite universe means an infinite amount of stars that have no obstacles in getting their light towards us. Of course, this also means that there are infinite stars that could be blocked from getting their light to us. But in an infinite universe proposed by Newton, who cares?

 

[russ_watters]

My argument is combinatoric. Not about the actual process of generating light per se.

But you have made an assumption that light is emitted at an infinite rate. You appear to be confusing that with emitting light at an infinite speed. You seem to have one question and one error.

Just to be clear; even if it were right, Olber's paradox does not result in an infinitely bright universe.

 

[FallenApple]

And why should that rule out the infinite speed of light and not the infinite homogeneous distribution of stars?

An infinite homogenous distribution of stars everywhere is more unlikely. They can use astronomical observation to note that the stars are not homogenous, which implies the existence of possible local deviations from homogeneity. Moreover, even if on average the the stars are homogenous, just by having an infinite amount of them, there is a finite probability of some configuration at some distance where nearly and infinite amount of light just hits us at once due to their infinite speed.

You could have 100 trillion stars shining upon us such that they are timed just right to hit the Earth all at once. And these stars can be googles of light years far from each other, it doesn't matter since the universe is infinite. So by combinatorics, infinite space means any configuration could happen, no matter how improbable. This is assuming that the universe is on average, homogenous in stars.

 

[FallenApple]

But you have made an assumption that light is emitted at an infinite rate. You appear to be confusing that with emitting light at an infinite speed. You seem to have one question and one error.

No, I have assumed each star shines light at a finite rate of their own. But with infinite stars, each one is shining a light particle at different moments(slightly different or just completely different, all possibilities happen due to the infinitude of stars) then every, moment in time, a light particle is emitted somewhere. Assuming that each star has their own rate that is slightly different. Then yes, the such a universe would have an infinite rate when considering all the stars in total, which is infinite amount of stars, according to the physics of the time.

 

[russ_watters]

No, I have assumed at each star shines light at a finite rate of their own. But with infinite stars, each one is shining a light particle at different moments, then every, moment in time, a light particle is emitted somewhere.

Sorry, I missed that you flipped it over...

...so at this point I'm not sure if you realize this universe you describe is not infinitely bright (except in a runaway extreme).

 

[A.T.]

But with infinite stars...

And what forced the people back then to assume that part?

 

[Vanadium 50]

How about an infinite amount of cars leave for Providence from every direction

A. It's infinite number, not amount.
B. Stars are not infinitely bright, nor are there an infinite number of them visible in the sky. Just look up!
C, You seem to be making many different (and mutually incompatible) assumptions at once, without clearly stating them.

N cars per day leaves Boston for Providence at 30 mph, and M (M>N) leave for elsewhere. How many cars per day arrive in Providence?
N cars per day leaves Boston for Providence at 45 mph, and M (M>N) leave for elsewhere. How many cars per day arrive in Providence?
N cars per day leaves Boston for Providence at 60 mph, and M (M>N) leave for elsewhere. How many cars per day arrive in Providence?

 

[FallenApple]

A. It's infinite number, not amount.
B. Stars are not infinitely bright, nor are there an infinite number of them visible in the sky. Just look up!
C, You seem to be making many different (and mutually incompatible) assumptions at once, without clearly stating them.

N cars per day leaves Boston for Providence at 30 mph, and M (M>N) leave for elsewhere. How many cars per day arrive in Providence?
N cars per day leaves Boston for Providence at 45 mph, and M (M>N) leave for elsewhere. How many cars per day arrive in Providence?
N cars per day leaves Boston for Providence at 60 mph, and M (M>N) leave for elsewhere. How many cars per day arrive in Providence?

Ok, in your example, N reach Providence at each of the 3 rates. So 3N.

But let's say this:

from city 1, at 0.0001 deg north west of Providence, N cars drives to Providence.
from city 2, at 0.00011 deg north west of Providence, N cars drives to Providence.
from city 3, at 0.00012 deg north west of Providence, N cars drives to Providence.
...
At every degree, at every break down of a degree.

How many cars arrive in Providence per day? As many as there are specific degrees in a circle. So infinite.

As to point B, yes, there shouldn't be a problem if there isn't too large an amount of stars. But during Newton's era, the universe was considered infinite. Looking up in the sky should show that there isn't infinite number of stars if speed of light was infinite, and the problem is resolved. Though, I think this would clash with Newtons infinite universe idea though.

For C, I'm making the assumptions of Newton that the universe is infinite.

 

[FallenApple]

Sorry, I missed that you flipped it over...

...so at this point I'm not sure if you realize this universe you describe is not infinitely bright (except in a runaway extreme).

Well, on second thought, maybe it takes too specific configuration to get infinitely bright everywhere.

But still, it makes sense that at the very least, it would be much brighter if speed of light is infinite, which was essentially my main point in the OP. I mean, infinite light speed implies we would be getting light from far away stars that we wouldn't have otherwise on a regular basis. This high brightness should be the case in a finite universe or an infinite eternal universe when there is no speed limit.

Whereas, we only see high brightness for finite speeds in an infinite universe.

 

[russ_watters]

Well, on second thought, maybe it takes too specific configuration to get infinitely bright everywhere.

What it takes is for light to go through stars so that the brightness adds instead of stars blocking light from other stars (or, for the temperature to increase without bound due to all of the extra radiation bouncing around). The standard setups of Olbers' paradox result in a universe where every line of sight ends on the surface of a star and therefore the brightness is that of the surface of a star.

But still, it makes sense that at the very least, it would be much brighter if speed of light is infinite, which was essentially my main point in the OP. I mean, infinite light speed implies we would be getting light from far away stars that we wouldn't have otherwise on a regular basis. This high brightness should be the case in a finite universe or an infinite eternal universe when there is no speed limit.

Yes, it can make for a brighter universe depending on the assumptions made about the large scale dynamics of the universe (infinite or finite, expanding or not, etc.).

 

[jbriggs444]

But still, it makes sense that at the very least, it would be much brighter if speed of light is infinite, which was essentially my main point in the OP.

Are you assuming an infinite homogeneous universe with a finite age?

 

[DrStupid]

An infinite homogenous distribution of stars everywhere is more unlikely.

And therefore there is no reason to favour it over a finit speed of light.

Moreover, even if on average the the stars are homogenous, just by having an infinite amount of them, there is a finite probability of some configuration at some distance where nearly and infinite amount of light just hits us at once due to their infinite speed.

There is no configuration where the amount of light goes infinite. It seems you are missing something (e.g. the reversed quare law for the intensity).

 

[russ_watters]

There is no configuration where the amount of light goes infinite. It seems you are missing something (e.g. the reversed quare law for the intensity).

Having spent more time than I care to admit trying to educate someone on this once, I can say that where this can come from is the assumption (on purpose or without realizing it) that stars are points.

 

[jbriggs444]

Having spent more time than I care to admit trying to educate someone on this once, I can say that where this can come from is the assumption (on purpose or without realizing it) that stars are points.

Eek. If stars are pointlike then there will not be a star in every exact direction one can look. Instead it will merely be the case that the stars will be dense in the sky. With probability one, no one star will occlude any other star and the luminous intensity will be infinite. [for an infinite, static, homogeneous, eternal universe]

 

[sophiecentaur]

How many cars arrive in Providence per day? As many as there are specific degrees in a circle. So infinite.

I think you are going off in the wrong direction with this argument. You are choosing a 'degree' as a fundamental step in angle size, which doesn't make sense but the question is considering a single track road (one dimension) - a much simpler statement of the problem.
Stars don't follow the 'trees in a forest' model, where you will see 'wood' wherever you look in an infinite forest (whatever the size and spacing of trees). That implies that either the universe is not infinite or that it is infinite and there is 'something going on with' the light from very distant stars. (Or both of course)

 

[Noel]

One car per day leaves Boston for Providence at 30 mph. How many cars per day arrive in Providence?
One car per day leaves Boston for Providence at 45 mph. How many cars per day arrive in Providence?
One car per day leaves Boston for Providence at 60 mph. How many cars per day arrive in Providence?

I think it depends on how many cars leave other locations for Providence each day, how many breakdowns occur, etc.

 

[sophiecentaur]

I think it depends on how many cars leave other locations for Providence each day, how many breakdowns occur, etc.

I hope that's a joke.