Thought Experiments
Einstein made
thought experiments famous. But he wasn’t the man who invented the concept. So
what is a thought experiment? Based on certain assumption(s), you go over the
logical consequences it would lead to. As Shane Parrish wrote:
“The purpose is to encourage speculation,
logical thinking and to change paradigms. Thought experiments push us outside
our comfort zone by forcing us to confront questions we cannot answer with
ease.”
So who came up
with the first recorded instance of a thought experiment? Not surprisingly, it
was the Greek Zeno back in 430 BC. He used it to “prove” that motion is an
illusion. Huh? His logic was this: assume the tortoise is 100 m ahead of the
hare. When the hare covers the 100 m gap, the tortoise would have moved a bit
ahead. When the tortoise covers that second gap, the tortoise would have moved
a little bit ahead. And so on it goes. How then could the hare ever catch up
with the tortoise, asked Zeno. What was the flaw in his reasoning?
Galileo used a
thought experiment to “prove” that heavier objects don’t fall faster than
lighter objects. Imagine a 10 kg body tied to 1 kg body. At what speed should
the tied entity fall? Slower than the 10 kg body would have fallen because the
1 kg body would be slowing it down? Or faster than the 10 kg body because the
combined weight was more than 10 kg?
In philosophy,
Plato came up with the famous parable of the cave
to ask whether what we perceived was
the same as reality:
“A group of people are born and live within
a dark cave. Having spent their entire lives seeing nothing but shadows on the
wall, they lack a conception of the world outside… At some point, they are lead
outside and see a world consisting of much more than shadows.”
Andrew Irvine even
argues that a thought experiment must require all assumptions to be supported
by empirical evidence. And it should be possible to prove it false. That aspect
though only applies to science, not other fields.
But why not just
do the physical experiment itself? As Barbara Massey explains:
“The thought experiment seems to be a close
relative of the scientist’s laboratory experiment with the vital difference
that observations may be made from perspectives which are in reality
impossible, for example, from the perspective of moving at the speed of light.”
Nor could one do
the ethics thought experiment of the trolley problem. If you had the option of
throwing a switch to kill one person instead of five who lay on the path of an
oncoming trolley, would you throw the switch? Would the answer change if the
one person was a known “bad” guy? Or a loved one?
Like I said at the
top, Einstein and physics aren’t the only ones to use the thought experiment
methodology.
Interesting blog. Don't know if those who do not know physics would find this idea meaningful! Maybe they will, since it is conceptually OK.
ReplyDeleteSince it was Einstein who made thought experiments "glamorous", I wish to mention here what I recall. Einstein and Neils Bohr had many years of 'thought experiment arguments' between them. Einstein was keen to pick a fatal, basic flaw in Quantum Mechanics while Neils Bohr was a staunch defender of the new physics. Every time Einstein came up with something clever and substantial by way of a thought experiment that he expected would derail quantum mechanics, Neils Bohr would rack his head for hours before a point that Einstein had missed would appear to him. That would ensure that physics principles are not violated yet and it was only Einstein who had missed a minute detail! Einstein would agree. He will move on to the next different idea, instead of giving up. Many years went by this way, both these stalwarts not tiring yet! Einstein's focus was to derail what is known as Heisenberg's Uncertainty Principle.
Closer to his end, Einstein along with two collaborators came up with a brilliant and an altogether different challenge that did not yield to picking flaws in principles. (It was not about challenging the Uncertainty Principle but focused on "how is it possible that an interdependent remote action at a far away place would take place at all, as it doesn't make sense".) The published paper is known as EPR Paradox. Neils Bhor was "shaken not stirred", if we apply James Bond dialog to the situation! :-) In their time, an experiment to verify the truth about Einstein's question was not even conceivable, let alone implementable. Both the stalwarts died soon after, neither of them knowing who wold win the argument.
Four decades (I think) passed by. Finally, the technology and methods got so advanced that experimentation became possible. The results showed that, although the implication was not at all understandable or explainable, quantum mechanics was still holding ground and Einstein's hope had got demolished. In later years, even better and more direct verification methods became available for experimentation for the same EPR Paradox issue, and quantum mechanics has won hands down several times.
The point I am trying to make is this: there could be sometimes a thin line between some thought experiments and real experiments. In many other cases it may not be so - they would forever remain thought experiments only!