My son asked if The Flash moves so fast, how can he see things. How can I easily explain this?

Answer by Thaddeus Howze:

Because Light is Faster than the Flash!

You can assure your son, Barry Allen as the Fastest Man Alive, is rarely in danger of running faster than he can see because light is almost always faster. In our universe, light is faster than everything!

The Speed Force

The standard answer to most things about the Flash is his relationship to the Speed Force, an enigmatic superset of cosmic energy in the DC Universe, which allows the Flash to perform abilities beyond the laws of physics.

The Speed Force is a concept presented in various comic books published by DC Comics, primarily in relation to the various speedsters in the DC Universe.

The Speed Force was the extra-dimensional energy that once powered all of the Flash's superhuman abilities. It is not like any other fundamental force.

Its origin is likely the same as most superhuman abilities found in the DC Universe, a byproduct of the mysterious omni-energy known as The Source and The Godwave.

The ability to access the Speed Force has been limited to only a few individuals in the DC Universe and when DC characters travel to the Marvel Universe, they are unable to access the Speed Force.

The faster the Flash moves the more likely the Speed Force is allowing him to manipulate the laws of physics such as inertia, momentum and force. However, if the Flash should start to approach the speed of light, he would have problems if he was not assisted by the Speed Force. The speed of light is the fastest speed in the Universe, that we know of at 186,282 miles per second or 300,000 kilometers per second.

When the Flash is patrolling Central City, he is rarely moving anywhere near his top speed. Most times, he is traveling well below the speed of light, probably no faster than a really nice race car, about two hundred miles an hour. This speed is fast enough he can get anywhere in just a few minutes. He doesn't have to stop for lights, or traffic because he is small enough to fit almost anywhere.

A quick way to think about how fast he is moving… 60 miles per hour means he is moving about a mile a minute. A trip to someplace 10 miles a way at a leisurely pace of 60 miles per hour means it takes about ten minutes.

If we think of the Flash moving about four times that speed, he could cover that same ten miles in a little over two minutes. More than fast enough to move around a fairly large city with no real traffic restrictions. This is also slow enough so he can get instructions from his friends at Star Labs over his radio. Even if something were twenty miles away, at a safe cruising speed of 240 mph, he is never more than five minutes from anything.

In an emergency, if the Flash really wanted to turn on the speed, he might increase his speed to just over the speed of sound at about 760 miles per hour (Mach 1). At this speed though, his ability to change direction is a bit harder so he uses speeds like this when he has lots of straight or gently curving road.

While this may seem very fast, race car drivers and pilots control their vehicles, at these speeds, with their well-trained human reflexes.

The Speed Force at work

The source of all human speedsters superhuman abilities is their connection to the Speed Force. Believed to be a subset of the Source, a cosmic repository of energies which power all superhuman ability, this power is uniquely reserved for and accessibly by Human speedsters and anyone utilizing technology which can also access this energy field.

And yes, there is a question of how people like Superman and Wonder Woman have super-speed but don't use the Speed Force. It appears they are able to, as a subset of their own abilities, use greater than human speeds but without the protection and limiters the Speed Force allows. This means when they use their powers, if they aren't careful, they can cause more harm than they might want.

When the Flash is running, the Speed Force surrounds and envelops him in a protective aura.

He can extend that aura to people he is carrying, so they are also safe from flying debris, wind burn, friction and other associated speed related issues. All of these energies are bled into the Speed Force and have no effect on the Flash or his surroundings, unless he wants them to. He can withdraw speed from other things or people and add that speed to his own.

Jay Garrick, the Golden Age Flash, steals speed from Superman, slowing him down and boosting himself ahead of the Man of Steel.

Most importantly, the Speed Force is augmenting the Flash's brain and his perception, speeding up his thinking process, helping him to organize and coordinate his movements, extending his awareness of his body so he doesn't touch anyone at the speeds he is moving. It would be disastrous.

Once the Flash starts moving at speeds faster than sound, the Speed Force goes into overdrive. Once the Flash is opening up his speed, he is faster than a bullet. To outrun a bullet he needs to be able to reach speeds of up to 1,700 miles per hour!

His reflex time is so good and he is so fast, he can, using the Speed Force, remove the momentum and energy from a bullet and pluck it out of the air, like a raindrop. Only the Speed Force would allow him to steal the momentum and energy and add it to his own.

When the Flash has to kick it up a notch, he might need to move at 4,000 to 8,000 miles per hour, and he still won't have any trouble seeing things. He reserves speeds like these for long distance country running because it is harder to navigate tight streets, particularly at these speeds.

When he starts moving this fast, nothing around him will appear to be moving in relationship to him. He is so fast, the normal world may as well be standing still. At these speeds, he is moving as fast as one of our nation's fastest fighter jet (Mach 5 to Mach 10).

Walking people and moving cars will appear to be almost motionless to him. And he is moving so fast, he will be invisible to them.

Here's where the Speed Force's effects become clearly evident to the external viewer.

Once the Flash reaches the speed of sound (about 700 mph at sea level) he should be capable of generating a sonic boom and a pressure wake capable of knocking people off their feet as he passes. But he doesn't.

Bugs striking him at this speed should have the ability to feel like bullets and anything hitting him from the road like gravel would have the damage dealing capacity of small grenades. But they don't.

Gravity no longer pulls him down from the sides of buildings and he is able to skip across the surface of the bodies of water, treating it just like a normal surface for him to run on.

At these speeds, his reflexes are so fast that high speed projectiles such as bullets are moving slow enough for him to actually track their movement and avoid them completely. But he won't do that, for fear they might hit innocent bystanders. He just grabs them out of the air and drops them on the sidewalk.

The Speed Force channels all of the effects of his motion, save the ones he wants to manipulate into the energy which powers the Flash. He is able to channel the energy of his movement through though the air and thus causes no disturbance he doesn't want to.

One of the benefits of his powers, however, will allow him to maintain the ability to think, move and react at those speeds. Even though he is as fast as a fighter jet in the middle of town, the Speed Force helps him compensate and think fast enough to maneuver.

So when is vision a problem for the Flash?

The Flash ran from Central City to Singapore and back in just over three seconds. This means he covered 9,300 miles there and back moving at an estimated 6,000 miles per second!

Remember when we said the speed of light was 186,282 miles per second, earlier, the Flash was barely moving in comparison. We measured in miles per hour. Now he is moving in miles per SECOND.

He could be said to be moving relativistically: moving fast enough to be measured as a percentage of the speed of light. This means when he ran to Singapore and back, he was traveling at 3/100ths of the speed of light.

At this speed, he may begin having difficulties seeing things that are not directly in front of him, because he is now moving fast enough he is distorting light as it approaches him. But this speed isn't really enough to worry about.

It's when he reaches extremely close to the speed of light, where he may only be able to see things directly in front of him because he is now faster than the light of things alongside of him.

This is the most extreme representation of the Speed Force, it gives a speedster who can sustain such speeds, the capacity to move, understand, think, act and react at those speeds. Such speeds are very difficult to control and it is unlikely most speedsters can maintain them for long.

Name a time the Flash's vision is affected by his speed?

In a battle against other speedsters, the Flash's powers are pushed, often to their limits.

A speedster calling himself ZüM, along with a group of other superheroes (the Hyperclan) wanted to replace the Justice League, and fought the league members. Secretly, they were White Martians, each with powers capable of making them nearly as strong as Superman. Each, however, seemed to specialize in their use of their powers and ZüM, specialized in Speed.

The speedster, ZüM and Wally West (the Flash of the era) had an epic battle which showed the Flash was capable of manipulating his own energy using the Speed Force and transferring that energy to an opponent.

The Flash mentions when he is traveling at relativistic speeds his vision is compressed so he can only see things directly in front of him. This also means only someone who can react to relativistic effects (like dodging a beam of light) can see or react to him. Zum learned this the hard way.

The technique he used to defeat ZüM was dubbed the "Infinite Mass Punch." The mass he channels from approaching the speed of light* would make his fist incredibly massive and capable of transferring enough energy to rival a small nuclear explosion, if the Flash wanted it to. All of this sidestepping of the laws of physics are courtesy of the Speed Force.

*Physics Fact: objects made of matter cannot reach the speed of light because the laws of relativity indicate, they would gain infinite mass and would require infinite energy to move them. Thus no object made of matter can reach the speed of light. (Which has weird implications for the Flash, but that's a Flash Fact for another day.)

In summary:

It's safe to say, when the Flash is doing his job from day to day, he doesn't have to worry about not being able to see things around him.

The Speed Force protects him from dangerous environmental conditions brought on from his use of super-speed.

It increases his awareness, reflexes and reaction time to compensate for his increased superhuman speed. His brain activity must be improved billions of times in order to keep up with his superhuman activities.

His awareness has some limitations, since the faster he moves, the less he is able to take in, particularly if he reaches speeds that are a percentage of the speed of light. The closer he gets to the speed of light, the less he should theoretically be able to see.

The Flash rarely gets to speeds where he worries about relativistic effects like compressed photons and the like, so there is nothing to worry about as the Flash fights the forces of evil.

However…

The Flash does have feats where he is faster than light. In many cases, much faster than light.

Over the decades, the Flash has been shown to be faster than a beam of light which means he must somehow act as a form of energy capable of moving faster than light. (In comics, its possible, in reality, it isn't. At least not yet.)

In this interstellar race, Wally is running many times faster than light. He is moving so fast, he is able to see the boundary to the Speed Force (the pretty rainbow colored wall). This barrier is where all speedsters who can access the Speed Force can end up if they travel too fast…(whatever too fast means for a particular speedster, it varies for each one). Objects which travel into the Speed Force enter a kind of nirvana or heaven and are reluctant to return to the world.

A last minute save by Krackl keeps Wally West from falling into the Speed Force.

In those comics where the Flash moves faster than light, we are forced to accept that somehow, the Speed Force compensates the Flash for the information he should no longer be able to see visibly and allows him to continue operating at peak efficiency.

There are too many feats to mention where this happens, so we, as readers, are forced to accept that the Flash and his abilities are the stuff of comics and pseudo-science, powered strictly by imagination.

There's nothing wrong with using your imagination. The great scientist and thinker Albert Einstein once said:

“Imagination is more important than knowledge. For knowledge is limited to all we now know and understand, while imagination embraces the entire world, and all there ever will be to know and understand.”

Just because the Flash is imaginary, doesn't mean you can't learn a Flash Fact or two related to speed, motion, momentum, relativity, gravity, mass and the other laws and effects of physics the Flash gets to thumb his nose at.

Lucky guy, eh? Now who's running to Italy to get me a pizza?

Who would win in a fight between Superman and the Flash? (includes a primer on The modern New 52 Flash – Quora)

Read more information about the Speed Force. (Comic-Vine)

Speed Force – Tracking the Flash – the Fastest Man Alive (a website about all things TV Flash-related)

Those Who Ride The Lightning – The companion site for Speed Force, (see above) with historical information about the Flash, his rogues and anything else you want to know about the Flash over the last 60 years.