# Does Flash age slower because of his ability to run at relativistic speed?

Due to Time dilation, time is perceived differently at greater speed.

Time dilation is an actual difference of elapsed time between two events as measured by observers either moving relative to each other or differently situated from gravitational masses.

Time dilation explains why two working clocks will report different times after different accelerations. For example, ISS astronauts return from missions having aged slightly less than they would have been if they had remained on Earth.

And, we know the Flash can run even faster than light.

Is the effect on his aging ever mentioned anywhere?

• In Justice League-Crisis on Two Earths, moving at super fast speeds actually hyper ages Johnny Quick (the counterpart to Flash in the parallel world). Commented Mar 22, 2013 at 16:34

The wikipedia entry you reference describes two opposing forms of time dilation, one that will make you age quicker and one that will make you age slower. Both have noticeable effect only on extremely extended or close to light speed movement. The ISS astronauts, for instance, said to have aged slower, by 0.007 seconds for every 6 months on the station.

Consider, however, that The Flash mostly runs around on Earth. The earth's circumference is about 40,000 kilometers. Even if the Flash runs at only 13% of light speed, he can go around the entire earth in one second. As I understand it, he spends 99% of his time in "normal speed", only gearing up for full speed when necessary. This means that to achieve a sizeable time dilation will take decades, probably. Maybe more.

(Disclaimer: I did not really run any numbers here, neither for time dilation or for aggregated time spent in near light speed. I'm going mostly by intuition here)

• If we ignore the amount of dilation involved, what's your take on the fact that Flash can run faster than light ? On those occasions, does time then run backwards for him ?
– Stan
Commented Mar 22, 2013 at 19:21

No, the Flash does not get any significant aging benefit because he is running at faster than light speeds. There are several limitations which need to be taken into account:

• He spends the bulk of his life moving at a normal pace and thus does not utilize his relativistic movement except in extreme emergencies. His average pace around the city is only around 180-200 miles per hour.

• Given the extremes of speed once you start reaching Mach 10 or more, the Flash, even with his speed aura is reluctant to approach relativistic speeds. More importantly, there are almost no reasons he would need to approach even ten percent of the speed of light while on Earth which would approach 6,706,166 miles per hour (circling the Earth 268 times in a hour).

• When he is moving at a percentage of light speed which varies from writer to writer, his speed is so great whatever feat he is performing happens and ends within a few seconds and rarely lasts for more than a few minutes tops.

The Flash empties an entire city in North Korea (2 people at a time in a few seconds).

• Relativistic aging benefits would only occur if he were maintaining a sustained top speed for a significant amount of time, say if he were moving from star to star. Depending on his top speed he might slow his aging considerable in comparison to the flow of time on Earth.

The Flash's powers are not clearly defined by the laws of physics, nor by the DC Comics franchise. We are left unfortunately to speculate as to how he defies or obeys the laws of physics as determined by the writer/editor team at the moment.

• Funny thing about the comic posted: it claims he managed to move 500,000 people 35 miles in "0.00001 microseconds", while moving "at a hair's breadth short of the speed of light". The speed of light is roughly 300,000 km/s, meaning that even if he did move at lightspeed, it would take him ~188 microseconds to make a single one-way 35 mile trip. To manage 250K - 500K trips in 0.00001 µs, he'd need to be moving at least 10,000,000 times the speed of light. If my math is correct >_>
– jono
Commented Mar 22, 2013 at 22:26
• @jono At one point, Tony Stark stored thrust in his transistors. We should just be happy that the authors know microseconds exist, I guess... Commented Mar 22, 2013 at 23:19
• He'd have needed to outrace light in any event. Unless Flash moved them all out of the way of the X-rays from the initial blast, they are as good as dead anyway. Commented Mar 23, 2013 at 3:08
• Also, he would need to slow down to pick up and deposit the evacuees, unless he wants to crush them to a pulp. This is a variation on the "Shouldn't Lois Lane have been sliced into three pieces when Superman catches her mid-air" Commented Mar 23, 2013 at 8:52
• Hurray for hand-waving! Commented Mar 23, 2013 at 16:03

For arguments sake, I would like to think that any time he does gain from the small amount of time dilation he might experience (as stated in more depth in the other answers) is lost due to his accelerated metabolism. It seems he uses a lot more energy and puts a lot more stress on his body when at full speed, so it would seem the two would likely cancel each other out.

• It's not the same thing. One is relative time perception, the other is physical deterioration. When we say "He's 50 but has the body of a 30 year old", it's not really the same as saying "He's been around for 50 years, but only experienced 30 of them". Commented Mar 23, 2013 at 8:53

My theory is (now it's not necessarily the case, but just a thought) if his body is being sped up meaning like in S1 of the CW's flash when Felicity asks if his newly gotten powers make him age faster which Dr. Wells doesn't answer but instead says "everything we're doing here is for Barry's own good". But to the point, if his speed powers were making him age faster, his accelerated healing should theoretically cancel it out.

• I edited out the last bit of your answer -- it was kind of ranty. Don't worry; no one's going to judge you for watching TV; the question is tagged [dc-comics] but doesn't specifically exclude the TV universe, o there's no problem. It might be good if you can find other references from the show to support your answer, though. Commented Nov 13, 2016 at 15:28

Well consider this: the Flash's metabolism is faster than any human's and as a side effect he ages slower. When a human gets older their metabolism gets slower and their cells begin to die, so because of that the Flash's metabolism, which as many fans already know, moves faster so then he would age slower.

• Wait, what? His metabolic processes are faster than other people’s, and so (therefore?) a natural and inseparable side-effect of metabolism progresses at a slower rate? That seems backwards. Can you explain how this works? Commented Nov 24, 2016 at 6:15

In the flash when felicity come to central city and Barry in on the treadmill that Cisco makes she asks if his body is sped up then won't he age faster and wells said no while his body is moving faster everything else is slowed down including how fast she ages that why reverse flash tell him they would be enemy's for centuries and reverse flash was from156 years in the future so there you have it the flash ages slower

• Which season/episode was this from? Commented Feb 9, 2018 at 19:10