Spaceships in Star Wars frequently use energy weapons for combat. Given that Sir Isaac Newton is the deadliest SOB in space, I was wondering if this also applies to the non-kinetic space weapons used in Star Wars. Do they have a maximum range after which the shot dissipates, or do they veer off into deep space and possibly hit some unlucky sod several millennia later?
Yes, in canon, the weapons have a maximum range. As demonstrated in this discussion talking about some of the dialog from the first movie, A New Hope, Han makes the comment that the TIE fighter is "almost in range" as they pursue it towards what they later discover is the Death Star. It's clear from the view through the cockpit that the range is fairly short for the weapons the Millennium Falcon was carrying. If you go by the math in the discussion, the TIE fighter was only about 300 meters ahead of the Falcon, making it a very short distance.
The next movie, The Empire Strikes Back, also makes it clear that the weapons from a capital ship like a star destroyer have a much greater range. The discussion on the same page as above discusses a sequence where two destroyers are coming at the Falcon. From their math, a maximum weapons range is at least 75 kilometers, possibly over 135 km, though an effective range would be much less against a small, fast moving target like the Falcon.
From the same movie, it is clear that a ground based energy weapon can have a much greater range and effectiveness, as the rebel ion cannon fires from their ground base and disables star destroyers in orbit around Hoth. Even a conservative estimate of how high those star destroyers would be orbiting would place that range at greater than 1000 kilometers if they were in a fairly low orbit around the planet. A more likely figure would be closer to 5000 km from the ground to their positions.
So, yes, from canon we can determine that energy weapons have a maximum range, and that the range varies based on the source of the weapon.
As a side note in comparison, in the X-Wing series of video games (which was of dubious canon state even before the Legends), the maximum range for energy weapons from fighters and small freighters like the Falcon is 1.5 kilometers distance, at which point their energy has dissipated enough to no longer be viable.
All beams over a given distance will lose focus. While the advanced technology may allow that to be a very large distance, there would still be a physical limitation as quantum mechanics will stop the physical device from being able to focus past a certain point. So like a magnifying glass the non-kinetic weapons need a strong focal point. You usually cannot set alight unless you have a very narrow beam.
Additionally while space is usually considered empty this is only mostly true and over a distance the beam would deteriorate interacting with radiation and background particles.
This means that the non-kinetic will keep going until it hits but will slowly disperse to have a weaker and weaker effect over a large enough distance. So while there is no actual hard limit range, you could probably apply an 'effective' range to these types of weapons.
Note: This question is based mostly of my understanding of physics and am unaware of any in-universe factors that would change this answer.
I'll disagree with BBlakes answer, in that laser weapons do not have have a minimum range. Yes Han did say things like they are "almost in range" but I think he misinterpreted the meaning. When Someone would say something like "almost in range" I believe they mean that the ship is almost within the ideal range in which pilots prefer to fire at. Any range past that ideal range and your chances of hitting are smaller and firing would waste energy you may need later in the fight.
Neither side wasting laser energy when the chances of hitting were so small
X-Wing:The Krytos Trap, Page 61
Here Wedge Antilles is in a dogfight and though he and his target have a line of fire on each other, neither fire until they are closer.
At 400 meters he flicked the lasers over to dual fire... One bolt hit the torpedo at 250 meters out.
X-Wing:The Krytos Trap, Page 45
This is an example of the sort of ideal firing range for an X-Wing, in this case, to hit a small target like a torpedo.
She stayed below and behind the TIE-fighter until shed closed the range to within 250-meters.
X-Wing:The Krytos Trap, Page 325
Another example of wanting to close range for an increases chance to hit.
Farther along he saw streams green laser-bolts of spraying out from he space station. At the extremes of range the fire did not seriously threaten the incoming fighters, but it did keep them away long enough to scramble it's TIEs.
X-Wing:The Krytos Trap, Page 53
This implies that, thought the laser would still damage their ships if they hit, the chance of hitting still suppresses their assault. A space station would not be limited by energy supplies, assuming this have excess, so this tactic is viable for them, while not for a small star fighter.
As Range dropped down to a kilometer... The X-Wing's four lasers fired in sequence, peppering the middle level...
X-Wing:The Krytos Trap, Page 305
So in conclusion, the example from this book imply,though they could be up for interpretation, that lasers maintain their intensity for a very long range with the penalty of accuracy. The optimal range could also have something to do with the zeroing of the lasers, as talked about in this question. (can't find it yet, will update later)