Einstein’s Theory of Special Relativity was reviewed in a previous post.  As discussed within that article the speed of light is a key component of Einstein’s equation E=MC2.  Here is the link to that post.


How can we put the speed of light—186,000 miles/second or 670,000,000 miles/hour—into any kind of perspective that we can grasp?  Let’s start in our own very small back yard.  If we were able to travel at the speed of light, how long would it take to reach various destinations within our solar system?


Traveling at the Speed of Light within our Solar System


The table below shows speed-of-light travel times between earth and the other planets of our solar system.  Distances between the Earth and the other plants vary, over time, by a significant amount—due to the elliptical nature of planetary orbits—therefore, the average distances have been used for calculation.

Note:  The maximum speed of the Apollo 11 spacecraft was 25,000 miles/hour.

Destination Avg Distance from Earth (miles) Travel Time at Speed of Light
Sun 93,000,000 8.3 minutes
Venus 26,000,000 2.3 minutes
Mars 49,000,000 4.4 minutes
Mercury 57,000,000 5.1 minutes
Jupiter 391,000,000 35 minutes
Saturn 792,000,000 71 minutes
Uranus 1,700,000,000 152 minutes
Neptune 2,700,000,000 242 minutes

So, traveling at the cosmic speed limit—the speed of light—it would take a mere 4 hours to travel to our most distant planetary neighbor (Neptune).  The distance to Neptune—on average—is 2.7 billion miles!  If you were stuck inside an Apollo-like spacecraft, plodding along at 25,000 miles/hour, that voyage would take you 4500 days (12.3 years).


Interstellar Travel at the Speed of Light

What about travel outside of our minute neck of the woods?  What would be the time and distance considerations for inter-stellar travel?

Alpha Centauri, at 25 trillion miles from earth, is the nearest star outside our own solar system.  An astronaut traveling at light speed would be in flight for ~ 4.2 years.  Put another way, Alpha Centauri is 4.2 light years from Earth.  Again, Alpha Centauri is our nearest solar neighbor within the vastness of the Milky Way galaxy.

The distance across the Milky Way is estimated at 100,000 light years, therefore, a journey from corner to corner—traveling at the speed of light—would take 100,000 years.  Almost unfathomable.

What about a journey to another galaxy?  Andromeda is our nearest galactic neighbor at a distance of 2.5 million light years from earth.  Let that sink in.  If you were travelling at a whopping 670 million miles/hour it would still take you an unimaginable 2.5 million years to reach the outskirts of Andromeda.  Talk about a severe case of jet lag!

It is difficult to comprehend anything that would dwarf the speed of light.  But, the vastness of the cosmos does just that.  The human mind can barely comprehend the implications of light speed, but, 670 million miles/hour is at least stated in terms that we can grasp.  Conversely, the size of our universe is truly unknowable.  Our minds are dwarfed by it and we, therefore, will always be confounded by it.


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