Why Interstellar Spaceflight is Hard

This was initially published in audio form as Burst 7 of the Wow! Signal. As part of the ongoing effort to tie this blog into that podcast and vice versa, we here present a slightly edited text version of the same.

This is a tutorial post, and is largely meant to bring some of our readers up to speed, since we are going to be talking about interstellar space flight more over the next months. If you have ever wondered by we can’t just get on a big rocket and fly to the stars, this is for you. If you already know why we can’t do that, then I think you might want to skip this one. 

The Fermi Paradox, Part 2

In my first post on the Fermi Paradox, I went over the basics, which I expect most readers are familiar with anyway. It can be summed up simply (perhaps over-simply) as:

• Our galaxy is plenty old enough for at least one advanced civilization to have completely colonized it by now, even at speeds much slower than the speed of light.
• "Completely colonized" should include our solar system.
• No one can make a persuasive case that this has happened.

 So, the simple version is: they should be be here, but they aren't. This presents us with a paradox.

I'd bet that some readers already have a few objections to the above, and over the next few posts we will take this apart and see where reasonable doubt lies.  This is the real value of the paradox: it serves as a sharp mental lens that forces us to question our assumptions. It should make us more humble about our understanding of how the universe works, and spur us into deeper research. The great unknown is great indeed, so let's go explore. The forward path for the human adventure could not be clearer, and one of the best signposts is the Fermi Paradox.

Sadly, this is not the only effect it has. Too many seize on the Fermi Paradox to jump to Grand Conclusions not in evidence. I promise not to do that. Instead, we will look for better questions than "where is everybody?" I haven't found one yet, but I see hope.

Speculation - the only way to fly

Ronald Bracewell

Here is another speculation, but probably not very original. In fact, it's a variation on the 1960 concept of a Bracewell Probe.  It's hard for me to imagine that some science fiction author or another hasn't treated this in some form.

In the future, we expect to be able solve these three broad classes of technological problem we haven't got a a handle on yet:

1. Very large sensors that can remotely sense distant planets accurately enough to ascertain their habitability with a high confidence.
2. The hosting of a human mind on a machine substrate - i.e. a truly intelligent machine.  This implies that the state of a human mind could be captured - "uploaded" onto a machine and captured in a data set. In other words, we could completely define what we now call the "self" in terms of data.  The crucial thing here (within an order of magnitude or so), is how much data.  Let's say it's about an exabit compressed, or  10^18 bits.  Some estimates are lower that, but I think we need lots of margin.  
3. Travel across interstellar distance, although the problems of doing so quickly ( a significant fraction of the speed of light and exploiting time dilation effects) may prove to be insurmountable no matter how sophisticated our technology is, and at present we have only the broadest concept of how to cheat the speed of light limit.

Let's assume we could do both 1 and 2, but item 3 could only be done slowly, so that it takes hundreds or even many thousands of years to travel between the stars.  This would be a hopelessly tedious journey for a human or superhuman intelligence, and all the mass required for reliable life support would only slow it down and limit options for deacceleration.

So, we would want to send only a small mass to another star system and it would take a long time and cost a lot of energy.   However, we can transmit information far more cheaply and at the speed of light.  You might need a really big and powerful transmitting array, but this is just scaling up from current technology.  To transmit an exabit in a year you would need a transmission rate of about 30 gigabits per second -  well within plausibility, even over interstellar distances.  The size of the receiving antenna you would need on the other side would increase with the distance (roughly 100 meters on a side at 100 light years, given plausible assumptions about  the transmitter, noise temperature and losses), but such antennas can be made from gossamer materials that can be folded compactly.