Answers to 6 Important Questions on Intergalactic Travel

Intergalactic travel is fascinating and is sci-fi on steroids. But the realities are mind-numbing to wrap your head around.

I’m going to answer 6 thought-provoking questions on the topic. This will give perspective on the hypothetical travel between galaxies. Because as it is, traveling to Mars is a monstrous challenge for humanity. All the while, our solar system is puny compared to our galaxy the Milky Way. Douglas Adams famously said,

“Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is.”

For added perspective, on August 20, 1977,  NASA launched Voyager 2. To this day, it’s one of the fastest human-made objects created. It travels at a blistering speed of 34,500 miles per hour.

The below artistical graphic shows Voyager 2’s distance traveled as of December 2018. On the x-axis, the units are Astronomical Units (AU). 1 AU is the distance from the Sun to Earth or about 93 million miles. The crazy thing is, Voyager 2 still has yet to leave our solar system after 43 years of travel!

current position of Voyager 2 as of December 2018
The current position of Voyager 2 as of December 2018 (Photo Credit: NASA/JPL-Caltech)

Keep this Voyager 2 visual in the back of your mind. Because we’ll now focus on the intergalactic scale in the next section.

#1 What are the biggest challenges of intergalactic travel?

intergalactic travel

Many complex challenges exist with intergalactic travel. The following is a short list:

  • The insanely far separation distances between galaxies
  • The ability of spacecraft to withstand the harsh elements of space
  • Limited propulsion technology
  • Inadequate amounts of energy to travel far distances

The travel distance hands down I find the most difficult to comprehend. The following table lists noteworthy distances, giving you further perspective on intergalactic travel:

Popular defined distances Total distance
San Francisco to Los Angeles380 miles
New York to Paris3,628 miles
Earth diameter7,920 miles
Earth to Moon238,900 miles
Earth to Mars206,400,000 miles
Earth to Jupiter453,000,000 miles
Sun to Pluto3,670,000,000 miles
Solar system diameter178,600,000,000 miles
Earth to nearest star24,984,000,000,000 miles
Milky Way diameter621,300,000,000,000,000 miles
Milky Way to nearest galaxy14,690,000,000,000,000,000 miles

Our primitive minds can’t wrap around and conceptualize these distances. Heck, even the distance to the Moon makes your head hurt. It’s because we think a 250-mile drive to our favorite campground is annoyingly far.

The amount of energy required to make the trip, we can better visualize though. But I can tell you it’s not as simple as fueling up a spacecraft from Earth and off you go. To illustrate, we’ll calculate the required energy to travel to Alpha Centauri, the nearest star to Earth.

Energy requirement calculation for a trip to Alpha Centauri

Alpha Centauri is about 4.24 light-years away from Earth. In our sci-fi calculation, we’ll assume our spacecraft travels at sub-light speed. This means we can make the trip in 25 years.

Important Note: the Voyager 2’s speed is 34,500 miles per hour. The speed of light is 670,600,000 miles per hour. Our fastest human-made object travels 0.00514% of the speed of light. 

For the Voyager 2 to travel to Alpha Centauri, it’ll take a little under 85,000 years!

First, we calculate the speed the rocket needs to travel to make the trip in 100 years.

Velocity = \dfrac{\text{4.24 light-years}}{\text{100 years}} x \dfrac{\text{9,500,000,000,000,000 meters}}{\text{1 light year}} x \dfrac{\text{1 year}}{\text{31,540,000 seconds}} = 51,084,337 meters / second

Next, SpaceX’s Falcon Heavy weighs 1,420,788 kilograms or 1,566 tons. It’d be fair to assume the spacecraft we send to Alpha Centauri would be at least 50 times as massive. Especially, if humans are on board. This calculates to 1,566 tons x 50 = 78,300 tons.

E_{k} = \dfrac{mc^{2}}{\surd[1-(v/c)^{2}]} - mc^{2}

E_{k} = \dfrac{(78,300)(300,000,000)^{2}}{\surd[1-((51,084,337)/(300,000,000))^{2}]} - (78,300)(300,000,000)^{2}

= 1.04 x 10^{20} joules

In 2017, the total world energy consumption was 585 x 10^{18} joules. So using ALL the world’s energy consumption in a year, we’d still not reach Alpha Centauri in 25 years. Crazy, right?!

Important Note: rockets requiring propellant for acceleration aren’t efficient. Your acceleration, \vartrianglev, relies on how much propellant your spacecraft can carry. The amount of propellant exponentially grows as \vartrianglev increases too. 

Today’s chemical and ion engines wouldn’t be adequate. They couldn’t make intergalactic trips or even interstellar trips. The propellant amount required would be magnitudes greater in mass than the spacecraft. Without enough propellant, the travel time would increase by thousands of years. 

From another perspective, today’s space rockets burn their fuel in minutes. To reach sub-light speed though, you’d need enough fuel to burn for years. Plus, the energy this \vartrianglev would create would be unworldly onboard the spacecraft.

#2 Why even travel beyond the Milky Way to new galaxies?

Christopher Columbus famously said,

“You can never cross the ocean unless you have the courage to lose sight of the shore.”

The passion to explore runs deep in our DNA. Humans have always been explorers, and this will probably never change. But beyond exploration, the following other reasons exist for intergalactic travel:

  • The Sun running out of hydrogen fuel and making the earth inhabitable
  • Gathering resources
  • Hedging against a potential doomsday on Earth (e.g. asteroid impact)
  • Discovering alien life

I know how farfetched intergalactic travel may sound. But those who quickly dismiss the pursuit, only need to flip through history. Hundreds of millions of years ago, sea organisms looked at dry land in amazement. I’m sure the perceived transition to land seemed impossible. This is now comparable to our pursuit of deep space travel.

What’s more, even intelligent machines would share our reasons for intergalactic travel. In fact, they have even more reason to look beyond Earth. Why would a machine made of nuts and bolts stay in a corroding environment on Earth?…

#3 What type of spacecraft would make intergalactic travel possible?

Let’s assume a spacecraft could withstand all the harsh realities of space. The only remaining problem to solve then is building enough speed to travel extremely fast. As we learned though, existing propulsion systems have huge limitations. As alternatives, scientists have proposed the following futuristic propulsion ideas:

Antimatter rocket

Antimatter is chemical fuel on steroids. According to NASA,

“While tons of chemical fuel are needed to propel a human mission to Mars, just tens of milligrams of antimatter will do (a milligram is about one-thousandth the weight of a piece of the original M&M candy).”

So why not use this amazingly awesome fuel today? For one, it’s VERY expensive and hard to come by. Antimatter mines don’t exist on mountainsides to dig into.

Secondly, matter-antimatter reactions produce a mix of high-energy destructive particles. Not only are these particles damaging to crew and equipment, but the energy is hard to control. So, you can’t steer your exhaust using the released energy. And if this wasn’t enough, storing antimatter requires large magnetic fields.

Bussard Ramjet

Use the ionized hydrogen found in space to produce thrust. A magnetic scoop made of electromagnetic fields will collect the ionized hydrogen. A nuclear fusion reactor would then consume the hydrogen to power a spacecraft. This means the spacecraft wouldn’t need to carry reactant mass from Earth.

Not having to carry huge amounts of reactant mass is a game-changer. Because a spacecraft’s total mass would greatly reduce. But, it’s not without engineering challenges though.

The hydrogen collector needs to be HUGE to capture enough hydrogen. But even then, the magnetic scoop would theoretically create drag. This would potentially cancel any generated thrust. Plus, who knows how much hydrogen even exists between galaxies?…

Solar Sail

This is a very appealing option because you don’t need to carry your reaction mass with you. Like the Bussard Ramjet option, you gather reaction mass from space. So, you’d use the radiation from stars for propulsion. The spacecraft’s reflective sails capture the momentum of light to drive it forward.

The problem is though, the sails need to be miles wide. Plus, in theory, this option works great for interstellar travel. But for intergalactic travel, the emptiness of space will engulf you. Stars will be but distant specs, far off in the distance.

Nuclear Pulse

Detonate nuclear pellets in the rear of a spacecraft. These detonations would propel the spacecraft forward. Sounds awesome, right?!

The problem is the number of nuclear “bombs” your spacecraft needs to carry on board. The weight would be tremendous, to reach the desired \vartrianglev.

You can now see a common theme among all the propulsion options. The reaction mass is the limiting factor. So, the logical approach is to create a reactionless driver. This way, you don’t exchange momentum with a reaction mass to accelerate your spacecraft.

Important Note: speeding up is only half the problem. The ability to slow down at your destination when moving at sub-light speed is an obstacle in itself. 

Then another hurdle is dust and atoms in space. The space between stars and galaxies is far from empty. There are tiny dust particles and atoms spread everywhere. These atoms on impact would deposit energy in a spacecraft causing local heating. The spacecraft material can then evaporate into space, and material properties can change.

Then there are the more dangerous dust particles. A tiny dust particle can destroy an entire spacecraft. You need to design an unworldly energy shield. Plus, reduce the cross-section of the spacecraft to limit exposed surface area. 

#4 Is intergalactic travel possible for humans?

spacecraft leaving earth into deep space

For humans, as in bags of meat, the journey isn’t practical no matter how you spin it. But, I always leave a sliver of hope, as you can never say never. In all likelihood though, the humans who may one day make this trip would be unrecognizable to us today.

We may restructure our DNA and strip much of what makes us human. This includes our meat bag bodies, sexual organs, physical senses, and so on. Only then, the trip for humans would have a sliver of hope.

I find this to be highly probable too. Just 100 years ago, who would’ve guessed we’d have the world’s information in our back pocket? The same advancements apply to human biological progression. With every passing year, humans are merging more and more with machines. In return, human intelligence levels up, and physical abilities improve.

In short, I can’t envision intergalactic travel with the current human biological architecture. But in the distant future, the set of rules constraining humans today won’t exist. Technology is supplanting the slow progression of biological evolution.

#5 Is intergalactic travel possible for machines?

One BIG advantage humans have over machines today is versatility. But if you look far enough into the future, machines will probably have the same versatility and MORE. And all without the high cost of keeping a human alive in space. Even if we’re talking about a cyborg, half human half machine.

Clearly, machines have a much likelier chance to make this near-impossible trip. In fact, compared to a human trip, the idea doesn’t sound too farfetched. Just think far into the future, where Artificial Super Intelligence (ASI) reigns. The ASI can make real-time decisions, without being tethered by biological limitations.

Plus, at these far distances, communication signals take A LOT of time to travel. For example, for our neighbor planet Mars, the radio signal travel time is 5 to 20 minutes. But, ASI wouldn’t need to communicate back with Earth to successfully make the trip.

#6 How will advanced physics and technology affect the pursuit of intergalactic travel?

As our understanding of physics improves, our desire for space travel will increase. We’ll learn more and more awesome new things about how the universe works. In return, our imagination of what lies beyond our solar system will further grow.

To play devil’s advocate, at a certain intelligence level, exploration may become unsexy. It’ll no longer be interesting or worthwhile. Because in the far future, our consciousness may be able to shift into a fully digital world. Then we can do ANYTHING we desire.

To top it off, the physical footprint of this digital world would be miniature in size. Think of a strawberry. So, why even bother with risky resource extensive explorations?…

Important Note: successfully traveling intergalactically conflicts with our current understanding of physics. We don’t know how physics truly works when it comes to the universe. 

Just in the past few centuries, our understanding of physics has greatly changed. So, who knows what changes await us only 1,000 years from now? Then, one can only imagine 10 million years from today. 


Intergalactic travel is even farfetched in sci-fi. Star Trek avoided these far travel distances as their ships remained in one galaxy. But what happens when our understanding of the universe greatly improves?

Stephen Hawking famously said,

“I don’t think the human race will survive the next 1,000 years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I’m an optimist. We will reach out to the stars.”

This thought exercise keeps me awake many nights for hours on end. Because intergalactic travel is just amazingly mesmerizing and head-scratching mind-boggling. At the same time, the cosmos is the best way to humble yourself. I wholeheartedly believe in this. Nothing else comes remotely close to striking the same emotions within me.

Now I know, intergalactic travel is probably millions of years away, if I’m being optimistic. Heck, even traveling to the nearest star is daunting beyond measure. But who knows, maybe some crazy sci-fi idea will one day become a reality. Think of warp drives and teleportation…no one said we couldn’t dream…

Do you think intergalactic travel is ever possible for humans? What fascinates you the most about intergalactic travel? What do you find to be the biggest challenge with intergalactic travel?


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