[Lyn & Steve Hardwick]

Lyn & Steve Hardwick  asked the Naked Scientists:
Hi Chris,

I love the show and listen to the podcast every week.

My question is do astronauts experience G forces in space or inertia forces. If they do, would it ever be possible to travel at speeds close to the speed of light, due to the fact the human body would be damaged during the high acceleration needed to achieve these speeds.

Regards

Steve
Perth, Western Australia

What do you think?

[Bored chemist]

Well, you can't get to the speed of light so the question's a bit tricky.
However, if you built some sort off spaceship that could accelerate at about 10 m/s/s then the people in it would feel the acceleration in just the same way they feel gravity on earth. In fact they would be more comfortable than a "traditional" spaceship where they would be weightless. It's much nicer to know which way is "down".
There are two problems with this. Firstly the engines you would need are outside the realms of current technology (and probably any  in the near future). You can accelerate at that rate for a while, but the power required to do so increases continuously. Sooner or later you run out of power.
The second problem is that people only live for a few decades- and that's not very long in terms of the distances in space.

Another point is that, once you are going really fast, turning corners is a problem.

[RD]

Radiation would also be a problem.
Interstellar space is not empty: it has about a million hydrogen atoms per cubic meter (approximately).
Hitting these atoms with a craft travelling close to the speed of light would effectively irradiate the craft with protons.

[Bored chemist]

Perhaps we should look after this planet; it doesn't look like we are leaving any time soon.

[syhprum]

The CMBR photons begin to look like gamma rays once you get going real fast.

[evan_au]

You only need to accelerate continuously at 1g (10m/s² for about 12 months to be approaching a significant fraction of the speed of light. After a couple of years, time dilation becomes quite significant.

But as Bored Chemist says, we know of no engine technology that could maintain these accelerations for long periods.

We do know of one fuel that would come close - antimatter. This has the energy density of E=mc². Reacted with an equal quantity of normal matter, and it releases a lot of energy. But with current technology, antimatter must be one of the most expensive materials manufactured to date; experiments at CERN use enormous amounts of energy to generate, capture and store a dozen or so atoms of anti-Hydrogen. Anti-Helium seems well beyond our current technology.

[Tomassci]

The heat from athmosphere is the problem. You will be like the 0.9 c ball. If you don't accelerate to c in space.