One of the superpowers of the last surviving son of Krypton is heat vision. It is explained that his alien physiology can absorb solar radiation and release it as heat vision, just like a laser. Does the Caped Crusader stand a chance against the super-powered Kryptonian? Bruce Wayne may have technology on his side but how much of an advantage will that give him?
Both Batman and Superman are good fighters but their methods and techniques are different. Superman depends on his Kryptonian powers while Batman relies on his intellect and technology. If we treat Superman's absorption as a form of photosynthesis and model his heat vision on the carbon dioxide laser, we can actually see if there are limits to Superman's powers. For example, how much energy he can deliver, and the time it takes to store that much energy in his Kryptonian cells. This may give Batman an advantage against the Last Son of Krypton.
A History of Superman's Powers from the Golden Age
The original Golden Age Superman of the 1930s didn't have the same superpowers he has during the Silver and Bronze ages. This Superman, originally created by Jerry Siegel and Joe Shuster, couldn't fly and certainly wasn't invulnerable. At best, he could leap over an 8th of a mile, run faster than a speeding train, and move large vehicles.
In Superman's pre-Crisis Silver.Bronze Age, his powers were substantially enhanced in the 1940s, in part to appeal and gain the interests of readers. His strength was increased to the point where he could even move planets. This time, not only could he truly fly, he could defy physics, and move faster than the speed of light. He also gained X-ray and heat vision, see across interstellar distances and observe events that occur on a microscopic and atomic level.
Superman became so powerful, he could do literally anything. The character was known to not only travel to other solar systems, but to other galaxies, universes, and time travel under his own power. It was not until after the Crisis on Infinte Earths crossover that John Byrne placed restrictions on the hero's abilities. This was done to make it easier for writers to come up with believable challenges for the superhero that had, until then, become too sensational or unbelievable for readers.
John Byrne's Superman was altered so that his powers gradually developed as he absorbed solar energy from a yellow sun. Superman gradually loses his powers as he is deprived of sunlight in the 1996 crossover series, Final Night.
In Man of Steel, Superman's powers appear closer to Byrne's vision of the hero. While he is strong, he puts effort into lifting oil rigs, flying and battling other Kryptonians. Though, there are differences. The DC Shared Universe Superman also derives his powers from certain elements of Earth's atmosphere in addition to the Earth's Sun.
So, although the Modern Era Superman's powers have increased since Byrne's departure from the series, we will use the Crisis Superman as a model to explore whether heat vision is possible.
Heat Vision and the Carbon Dioxide Laser
We can use the carbon dioxide laser as a model for Superman's heat vision. This laser is used in industry to cut, weld, and engrave metals, something we have seen Superman do in both the comics and movies. The CO2 laser works by exciting carbon dioxide molecules to produce laser light in the infra-red range. Given the same type of molecules is found in his body, this is a good choice to model heat vison.
Infra-red radiation is invisible, but heat vision is primarily seen as red beams in both the comic books and movies. This is probably done more for visual effect than anything.
Solar Absorption and Photosynthesis
Though Superman is Kryptonian and the method he absorbs solar radiation might be different, we will assume it is similar to photosynthesis. Photosynthesis is a chemical process that uses energy from sunlight to convert carbon dioxide into sugar. A plant can then use these sugars for energy or as the building blocks to more complex cell structures. A massive tree's structure, for example, is built using the carbon dioxide in the atmosphere and the energy from the sun.
Instead of being chemically based and producing sugars, we will assume that Superman's biology allows him to store energy; Superman is essentially a living solar battery. While it is possible his uniform can channel solar energy to his skin, we will assume he can only absorb sunlight through the uncovered parts of his skin, i.e., his hands and face. This gives us a total area of 0.06 square meters to work with if we add the area of his face and the front and back of his hands; we assume a 20cm face diameter and his hands measure 8 cm by 20 cm rectangle.
While plant photosynthesis is very inefficient, typically using around 1% to 5% in real life, the theoretical values are very different. The process has a maximum efficiency of 11% but, at the molecular level, the theoretical limit is 25%. We will assume that Kryptonian physiology is much better than Earth-based plant life and use this value.
The amount of sunlight that falls on the Earth's surface in a given area, or solar insolation, is 1367 W/mÃÂ² (Watts per meter squared). If we multiply this by the area of exposed skin, we can calculate how much energy Superman absorbs per second. This is equal to 20.51 joules per second.
Superman frequently uses his heat vision to melt and cut through steel. The melting point of stainless steel is about 1440 degrees Celsius (2624 degrees Fahrenheit). We can calculate the energy needed to raise steel from room temperature to the point where it melts (specific heat capacity), and then the energy needed to vaporize it (heat of fusion).
We will also assume that the beam is no larger than Superman's pupil, around a diameter of 6 millimeters (0.24 inches). Most lasers can also cut to depths of 5 cm (a little less than 2 inches) easily. Given the density of steel is about 7900 kg per cubic meter, Superman would vaporize about 11.2 grams (0.4 oz.) of steel at any one spot.
We can now figure out how much energy the Son of Krypton needs to vaporize a spot of steel. The specificic heat capacity of steel is 620 joules per kilogram per degree Celsius, and the heat of fusion is 247,000 joules per kilogram.
This is by no means a small amount of thermal energy. This amount of thermal energy can heat a cup of coffee in about six seconds, so it really helps to be from Krypton when you are in rush in the morning. There are days when microwaves just do not cut it!
Laser Eyes and Heat Vision
We see Superman needs close to 12,600 Joules of energy to melt one spot of steel. It will take about 612 seconds, a little over ten minutes for Superman to absorb this energy while wearing his suit. This, of course, assumes his physiology is 100% efficient and is able to transfer all the stored solar energy from his cells to his eyes. The typical carbon dioxide laser's efficiency averages about 20%. If Superman's eyes are anything like this, he will need to spend closer to 51 minutes in the sun.
Fighting the Man of Steel... and Winning!
The idea of Post-Crisis Superman needing to recharge is seen in the Infinite Crisis and The Death of Superman story arcs. In both cases, Superman needed to spend extra time under the Sun to fully recharge. This means Superman's tremendous superpowers are not limitless. While heat vision is an awesome weapon, the time it takes to recharge means he can not use this power often.
This could but may not give Batman the advantage he needs to fight Superman. In Man of Steel, he is portrayed as being stronger and more powerful than Zod due to his lifetime of exposure to Earth's yellow sun. While it is possible for Superman to unleash all of his energy reserves into heat vision to vaporize Batman, doing so would be unwise. If that gambit fails, Superman would be no stronger than the average human being, and easy to defeat.
Of course, Superman is an alien. There is no telling how much solar energy he can actually store. Like any good fighter, the Man of Steel must pace himself, and use his solar reserves judiciously. Batman also faces a similar problem. Being human, albeit a very physically fit one, he will eventually suffer the effects of fatigue. While the fighting startegies of both heroes are different, their physical limitations does open the possibility for one to defeat the other.
In short, Batman could win in against Superman's heat vision if he plays his cards right.