Question: Do you think in the future your research will allow you to move much larger objects with lasers?

Andrew McKinley answered on 22 Jun 2010:

This is a question we get asked a lot! It would be really cool if we could do it, but there are a few problems. The force of light is *tiny* – we can’t feel light pressing us down (even though it is), but the brigher the light, the bigger the force. Now, the problem is that when we move things around we need to shine enough light on it to have enough of a force.

The lowest power laser pointer that we can buy has a brightness around 100x that of the sun (that is there are more ‘photons’ – packets of light – passing through that 5mm circle than there are from the sun at the earth’s surface). We use a laser that is 100x brigher than this laser, and then we concentrate it on a surface that is 1000x smaller. This means that the effective brightness to move a *cell* is 10,000,000x brigher than sunlight! Can you imagine how bright light would have to be in order to move something that we can see? To move a marble of 5mm across, we would need light that is 10,000,000,000,000,000x brghter than sunlight (the brightness required scales with the volume of the sphere)!!

Now, we need to make sure none of that light can be absorbed by the marble – unfortunately, even the best marbles will absorb tiny amounts of light. Tiny amounts of this light though will still be an awful lot of energy, which will cause the marble to heat up. Under these circumstances, unfortunately it isn’t a case of “can we move the marble with a laser”, it’s rather a case of “will the marble still exist at the end of the experiment”!!

Sorry to let yo udown on that… But it would take an unrealistic amount of energy to do it 🙁
It’s still pretty cool that we can do it on cells though!