Really high speeds are out of our ordinary experience, and can be quite hard to apprehend. Is the speed of a rocket to the moon closer to a person walking or to the unmovable wall of the speed of light? In this article we will see a graded approach to appreciate how fast things and people can move, and at which point in our history each speed interval was (or will be) achieved.
A grading scale by factors of ten will make it easier to understand high speeds.
We start at a comfortable pace of 1 meter per second, which is 3.6 km/h or 2.2 miles per hour (mph). We are definitely in the realm of every day speeds for now.
This relatively slow pace is easy to achieve by a walking person, and indeed for animals of all kinds. Many turtles can move faster than this! It is however not so easy for bacteria and other unicellular animals to reach 1 m/s on their own; a protozoo in the wind is out of scope for our purposes of self-propulsion. We may assume that the first living organisms to move this fast roamed the sea, perhaps the first jellyfish. For instance the box jellyfish can move at up to 2 m/s. So this speed may have been reached by our remotest ancestors around 500 millions of years ago!
We are now at 36 km/h or 22 mph, still below hypervelocities. It is understandably hard to know when animals first breached that speed; perhaps the first sharks some 300 millions of years ago.
As to humans, we are near our top running speed: Usain Bolt can run 100 m in less than 10 seconds, with peak speeds of 12.42 m/s. But our ancestors have been great runners for a long time, and surely they could run downhill attaining high speeds. So our most athletic peers have been moving at this speed for maybe a few million years. The advent of horse riding put this crazy pace within the reach of most people around 6000 years ago.
At 360 km/h and 223 mph, we have reached a very interesting point in our scale. No known animals are able to reach this speed except perhaps for the peregrine falcon, which has been clocked at 389 km/h: it essentially flies up and then dives at terminal velocity.
With human artifacts the issue is contended. A modern compound bow can reach 347 feet per second (105 m/s), and crossbows can be even faster at 460 fps. But it is doubtful that ancient weapons could reach these speeds. So throwing stuff at above 100 m/s is probably a modern achievement that had to wait for firearms, like the 14th century arquebus which could shoot at 300 m/s.
But projectiles are just one side of the story: when was the first time that a human reached this speed? This we know exactly, apart from people falling from balloons or other accidents. Wikipedia’s page of aircraft records lists the date as 1922, on a Curtiss CR piloted by the father of the USAF. Less than a century ago! Nowadays there are a variety of vehicles that can exceed 100 m/s, from cars to trains.
At 1 km/s, 3600 km/h or 2237 mph, we are now at almost 3 times the speed of sound (Mach 2.9 to be precise).
I’m sad to report that the SR-71 “Blackbird” spy plane, while being wonderful in many other respects, did not officially reach this speed; instead it flew at 3,529 km/h, or a paltry 980 m/s. As a consolation there are unofficial records that go beyond that.
Anyway there are plenty of rocket-powered planes that have flown faster. The North American X-15 has the current record at 2020 m/s (7270 km/h or 4517 mph), reached more than 50 years ago in 1967. At this speed it could have crossed Europe from Lisbon to Moscow, or the continental US from San Francisco to Washington DC, in about half an hour.
We are now at 36,000 km/h or 22,370 mph, firmly in the realm of hypervelocities. Going around the Earth at this speed would take around an hour (the ISS takes 90 minutes). Incidentally, we are really close to the escape velocity from our planet.
Even though conventional guns cannot go beyond 2.3 km/s, it is not impossible to send projectiles beyond 10 km/s using exotic guns. To calibrate how much energy we are talking about let us look at the collision of two satellites in 2009, a high-tech Iridium and an old Russian military satellite, which crashed at a relative velocity of 11.7 km/s. A rather conservative estimate gives an energy of 6.22 MWh. With more probable assumptions of one ton moving at 10 km/s we would get around 14 MWh: this is enough to power a typical home in Europe for two years (and in the US for one year). Think about a fridge, air conditioning and all other appliances working for two years!
As to human travel, the Guinness World Records webpage lists the Apollo 10 mission as having reached 11.08 km/s during re-entry into the Earth atmosphere, well beyond our milestone. That record has not been topped since 1969. In less than 50 years flying humans breached three steps in our scale, from 100 m/s to 10 km/s, and none since! Which if you ask me is a bit sad.
The speeds at this point in our scale become harder to understand: 360,000 km/h or 223,700 mph, which means one hour to reach the moon. We have now officially surpassed the escape velocity of Jupiter, the biggest planet in the solar system, which is only 60 km/s.
Particles at dust accelerators can exceed this speed. But the first human-made object to reach it was not a speck of dust; probably it wasn’t even a rocket or a deep space probe, but a humble manhole cover. It was launched by a nuclear explosion that predated the Sputnik mission by a few months; so it may have been the first human-made object in space (or it may have disintegrated in the atmosphere). Original sources estimate its speed at 66 km/s, while others put it well above 100 km/s.
This kind of speed is probably outside the realm of rocket-powered human travel: some kind of gravity assist will probably be required if we are ever to achieve it. And going this fast is a requisite for human exploration of the outer planets without getting burned by radiation in deep space. But we are not even at Mars yet, so sadly this next step is likely going to take a bit longer, at least until 2075.
Now we can escape cleanly even from our sun, which only requires 617 km/s; or even from our own galaxy, the Milky Way. It is interesting that we have found quite a few stars moving almost this fast within our galaxy, and some moving faster.
We are definitely out of reach of human projectiles at least for now, which we should be thankful for. At this tremendous speed the bomb that destroyed Hiroshima, Little Boy, would cause 35 times more destruction from the kinetic energy of the impact (2.2e15 J) than when it was detonated (15 kilotons or 6.3e13 J).
We are not close to sending anything in space at this speed anywhere. The Parker Solar Probe is expected to reach 190 km/s in 2025, which falls quite short. We would need radically powerful nuclear propulsion such as that proposed for Project Orion, an interesting concept that was quickly abandoned. But not before it was proved to be feasible! So not all hope is lost.
Is there no end to this madness? In fact, at 10 thousand km per second we are not even close to the Universe’s maximum value (300 thousand km/s). This kind of speed is necessary to escape a large white dwarf star such as Sirius B (5200 km/s).
To have an idea of how slow we are still going, it would take about 132 years to reach Alpha Centauri. Going a little faster would make it much more interesting. There are plans to launch micro-spacecrafts at 15% of the speed of light (0.15 c, or 45,000 km/s): each would weigh a few grams and be accelerated using powerful lasers, reaching their target planet Proxima Centauri b in around 30 years. Many technologies need to be improved by orders of magnitude so the mission is purely speculative by now.
We are now nearing the speed of light. Even this fast it might not be possible to escape from a neutron star.
The only projectiles ever launched by humans at this speed are probably atomic particles in particle accelerators, which can get really close to the speed of light.
As to transporting humans at this speed, the tremendous energies involved make it quite impractical. Just accelerating a human of 50 kg (110 lbs) to 0.33 of the speed of light c would require 65 megatons of TNT, which is more than the energy liberated by the largest hydrogen bomb ever exploded (50 megatons of TNT). Even at 50% efficiency it would take two Tsar Bombas, and this is without taking into account any vehicles or life support. Keep in mind that vehicles made to travel much slower such as cars weigh more than a metric ton, and that the Apollo 11 lunar module (which only had to keep its crew of three alive for a few days) weighed more than 15 tons. Accelerating just this module to this speed would require 19 gigatons of TNT, which is almost 20% of the energy output of the whole planet in 2001. On the upside, it would take only 13 years to reach Alpha Centauri, and due to relativistic effects its brave occupants would only have to wait for 12.5 years. How they would stop once they got there is another story.
At this point we have now officially surpassed the fastest speed possible. But not everything is lost! Tachyons are theoretical particles that might move faster than light; actually they should travel faster than light, so they would appear to travel backwards in time. It is not clear how Physics would work, or if they might ever interact with ordinary matter (called brachyons in this formulation).
Of course there have been many fictional depictions of hyperspace, or faster-than-light travel. A popular example of hyperdrive is depicted in Star Wars. For now there are no realistic ways of achieving these speeds so we will stop here.
Thanks for coming with me along this tour of increasing speeds, I hope you found it half as interesting as I did.
Wikipedia has an interesting list of speeds.