We've all been there. You take your keys to go buy groceries over at Alpha Centauri, until google maps tells you that it's a 5 million year journey by car at current traffic. So you decide to bail on it, and use that time productively by watching Downton Abbey. Interstellar travel has baffled scientists for ages. The vast interstellar distances, and 5 or more lightyears of distance between two adjacent stars, is simple far too big for humans to ever cross. 5 may not seem like a distance too large, but a lightyear is a huge distance. As a matter of fact, it is an unfathomable amount of distance. In just one second, light can take a round around the earth. Over the Taj Mahal, over the Eiffel tower, over the pacific ocean, over the vast stretches of desert in Australia, and back. 7 times. A plane flight just a 14th of that distance takes 15 hours! It can do that in a second, imagine an year. Photons continuously  flying through vast empty space, at a constant speed of 300,000,000 metres every second. For an year. Imagine a distance of 5 lightyears between two neighbouring stars! So is interstellar travel, impossible.

Interstellar distances are simply far too large to travel. This has 3 reasons.

1. The wait calculation. In his paper 'Interstellar Travel: The Wait Calculation and the Incentive Trap of Progress', Andrew Kennedy introduced a rather interesting concept to space exploration, often denoted with this equation: 

Here's an example to explain this. If I launch a mission to pluto today, and say it was going to take 50 years to get there, it would be very likely that enhancements  in technology 15 years later, which allow this journey to be made in 25 years, allowing the new spacecraft to get to pluto before the first mission does. This is the Kennedy Wait Calculation.  

2. The cosmic speed limit. Einstein, in his paper 'The special theory of relativity'  of 1905, German physicist Albert Einstein introduced a concept that cause the largest paradigm shift in physics since the renaissance of the 17th century. He associated two concepts that had never been associated before. The mass of an object, and the speed of light. He showed us this:

                                                                     

                                                                           E = mc 2            

He showed that the mass of an object increases rapidly, as the speed of an object approaches that of light, making the amount of energy needed to accelerate it, infinite. And if you know me, you know that is there is one thing my scientific mind is afraid of, its infinity. Enough of that.

3. Those damned gas prices. Yup. Gas prices. Space exploration consumes immense amounts of liquid hydrogen or propane. Let's say you don't travel at the speed of light. Perhaps you travel 50% the speed of light, or 150,000,000 m/s. You need way too much energy to pull off something like that. Not just that, the immense weight that the craft will have to carry, the math just doesn't check out. #engineeringproblems           

So can you not travel interstellar distances?

         

Well, no. It's not. As a matter of fact, we have travelled interstellar distances.

Presenting the voyager 1.

On a warm florida summer evening, September the 5th, 1975, Florida's residents for standing on rooftops, and waiting. For what? You may not know what, but that day, hundreds of the world's finest  scientists at NASA were gearing up for the longest deep space mission in the history of deep space missions. Standing on the hot ground at launchpad 39b at the cape canaveral air force station. It was big. The tall majestic rocket towering, and resting like a sleeping dragon. Inspite of the warm evening that that was, the body of the rocket was covered in frost, as the liquid hydrogen condensed atmospheric water. The engines made a periodic deep rumble, like a deep breathing dragon in deep slumber. It was time. The mission control lights went on. Fuel. Check. Ignition. Check. Land clear. Check. One by one the check light grids in the apollo mission control center, 8 km away, went on. Another one. And another. 10 minutes later, when all tests were complete, and the timer was coming down to the last 30 seconds, the rocket shook. Massive amounts of smoke rushed out of the rockets. 10, 9, 8, 7, 6, 5, 4, 3, 2, 1.. Main engine start. A loud ear splitting sound heard 100s of kilometres away. A huge rush of gas rushed out of the chamber, and a massive explosion pushed the rocket up. The rocket accelerated, faster, and faster, and faster, before reaching an incredible speed of 12km/s.  5 minutes later, there was the distant sound of dragging their lawn chairs off the terrace back into their homes. For the residents of florida, this was a hour of excitement, after which they went on with their lives. Little tammy went to sleep that night, but the voyager 1 did not stop, nearing speeds of 62,000 km/h, it had officially become the fastest man made object ever, as it remains to date. Tammy went to school the next day, and greeted his third grade teacher, the rocket was still going, relentlessly through space at a constant speed. Tammy got off school for christmas, the rocket was still going. He lived an endless procession of days, and routines, he graduated high school, 10 years later, the rocket had not slowed down a second. Tammy got into MIT, still the rocket was going. He graduated, got a job, got married, the rocket was still flying across the universe at the same speed. Little Tammy, not so little anymore, got a son. The rocket still did not stop. His son grew up, and 35 years after the launch, the rocket had not even slowed down, continuously streaming never seen before data to several generations of scientists. It was 2012, August 25th a staggering 35 years after the mission had started, half the team that had worked on the mission had passed away, when NASA got a sudden spike in their data streams. The voyager 1 was picking up heavy disturbance in the solar radiation levels, they were rapidly declining. As hundreds of scientists looked hopefully at the screens above. At 19 billion miles from the sun, the voyager was now on the edge of the heliopause or the edge of the solar system, where none of the sun's radiation reaches. The voyager 1 had become the first human made object to be in interstellar medium. It was 19 billion kilometres for a ship, but a huge leap for ship-kind.

But here's the catch. The voyager 1, even after 35 years of continuous flying has made it only beyond the solar system. The closest star to our own, is Alpha Centauri C,  often called proxima centauri, 4.23 light years from the sun, 'proxima', meaning close, in greek. 4.23 lightyears at the  voyagers speed is 80,000 years of continuous travel. The plutonium 238 nuclear reactor on board was only powerful enough to power the onboard instruments for 50 years, which leaves just 10 years before the voyager becomes a floating beacon in space until it is inevitably intercepted by a star.