The Predictive Power of the Slinky

Back in 2009, an earthquake struck L’Aquila in central Italy that resulted in the deaths of more than 300. A group of six scientists and a government official were blamed for providing reassurance that an evacuation was unnecessary and as a consequence were sentenced to six years in prison for negligence and malpractice by the Italian government.


This cautionary tale highlights a very important part of science: uncertainty

Never make predictions, especially about the future.
— Said by many via

Similar words of wisdom have been spoken in many contexts: weather forecasts, investing in the stock exchange, sports, etc.

As mentioned in a previous post, building a scientific model that can accurately predict possible outcomes is very difficult if not impossible. Ignoring these cautions, science constantly strives for predictive power. Predictive power that a slinky may have.

How can a slinky make predictions?

Want to see something amazing?

Take a slinky and hold it out in front of you fully extended. As you let go of the top, watch the bottom of the slinky. You might notice something very odd…

the bottom does not move right away.

A quick internet search will reveal that many people have recorded this phenomenon and even slowed it down so we can fully appreciate what happens. Check out an example below:

When you release the top of the slinky, the bottom part of the slinky does not yet ‘know’ it is falling. The top coil slams into the next coil and this pattern continues until the last coil is hit by this cascade.

This observation is not limited to Slinkys

A friend of mine challenged me with this question: what if the motion of a slinky could be applied to other aspects of our world: time, the transfer of energy, cause and effect.

The truth is, it does! 

Radiolab discusses this very topic in their episode: what a Slinky knows.

The podcast episode points out that this time delay for information transfer applies to not just a slinky but to everything. You will not know something has happened until the wave of information hits you.

We will always be a victim of what is coming at us that we are not yet aware of. Luckily, the time delay does not seem to be very long.

Dr. deGrasse Tyson provides a great illustration of how this would play out in the Radiolab podcast mentioned above if our sun were to suddenly disappear from our solar system.

We would not see or know the sun was gone for roughly 8 minutes and 20 seconds. 

     Blissfully unaware of the impending dangers behind her, this photo by      Victoria Nevland         beautifully captures the inevitability only a Slinky may know.

Blissfully unaware of the impending dangers behind her, this photo by Victoria Nevland beautifully captures the inevitability only a Slinky may know.

What does this odd fact teach us about the universe?

Is there such a thing as destiny? This question has always fascinated me. At least on the very local timescale, a slinky tells us that perhaps there is such a thing.

The next romantic notion of mine is that perhaps we can somehow use this fact to predict the future.

Being at the bottom of the slinky, can we somehow monitor the top of the slinky and preemptively adjust accordingly?

 If the earth was the bottom of the slinky and the top the edge of the universe, could we somehow notify ourselves an asteroid is coming our way. That is, once the asteroid hits the top of the universe, the information exchange begins and we wait till this information reaches us at the bottom.

Perhaps Casey Stengel’s warning about predicting the future applies to this case as well. Or maybe reducing this time delay is the key to making better predictions. Regardless, making predictions is a risky business and there will always be uncertainty.

What do you think? Is there any point in thinking deeply about the knowing of a Slinky or does dropping a Slinky in this way simply represent an oddity of physics?