This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
New technology is developed each year that lets us measure things that are smaller, colder, faster, or farther away than ever before. But there are some things, even with all of this technology, that we just can’t measure.
What if we wanted to measure a certain property in the Earth's core? Despite what movies like “The Core” would suggest, scientists cannot just go there and take a sample.
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What if we wanted to find out how radiation affects a material after 50 years of exposure? We would not want to set up an experiment and then have to wait 50 years for an answer.
That is where models come in.
Models are approximations of real objects or systems that integrate information from real-world measurements and use it to predict the behavior of that object or system under new conditions.
You deal with models every day. Some of them are scientific, like the ones that meteorologists use to predict the weather. Some are more personal, like the mental model you use to try to predict how your sister is going to react when you tell her that you broke her replica spaceship. These both take in data – weather systems or your sister’s past behavior – to make a prediction about the effect of exposing that system to new inputs – a cold front or a broken spaceship.
In order to make the most accurate models possible, scientists need to take into account as much data as they can when creating them. Once a good model is built, researchers can use it to test many different scenarios.
Think about the example of the three men who tried to escape from Alcatraz Prison in 1962. This prison, which is on a rocky island in the San Francisco Bay, was believed to be impossible to escape. It is surrounded by cold water and very strong currents that could easily sweep you out to sea. But on June 12, 1962 three prisoners made a raft out of ~55 raincoats and tried to paddle their way to land. Except for a single paddle found near Angel Island, they were never seen or heard from again. Many people have wondered if it would have been possible for them to survive.
Alcatraz Prison stands isolated on an island in the middle of a cold bay (Credit: Christian Mehlführer)
The Mythbusters, the well-known television hosts who dramatically put controversies to the test on their show, famously tried to test whether such an escape would be possible in true Mythbuster style: they built a raft out of raincoats and filmed themselves trying to make it to shore. Though they did make it, and they did try to reproduce the conditions as well as they could – all the way down to the raincoat raft – they still were only able to test one specific scenario.
Now consider the group of scientists who had created a highly sophisticated model of the San Francisco Bay for their research. They are investigating the potential impacts that changes in sea level or flooding could have on the hundreds of thousands of people who live in the Bay Area. This model has sophisticated details about the bottom of the bay, the topography of the land, and even can take into account currents and times of day. The researchers need this level of detail to be able to make predictions about conditions in the future.
After watching the Mythbusters episode about Alcatraz, one of the researchers realized that they could also use their model to look at specific moments in the past – like the moment of the prisoner escape.
No one knows for certain exactly what time the prisoners left in their boat, but it is generally believed to have been some time after dark on June 12, 1962. The researchers integrated information about the currents from the tide gauges from the night of the escape into their model. Unlike the Mythbusters, they were not limited to testing a single boat at a time.They actually released 50 virtual boats at a time from numerous possible escape points around the island and even included the effects of paddling into their simulation.
By releasing a set of 50 “boats” every 30 minutes from 8pm until 4 in the morning, they were able to test hundreds of possibilities. For any of the escape boats released before 11pm - which had previously been the most commonly believed time frame for the escape - the researchers said that the prisoners’ chances of surviving would have been “practically zilch.”
Between 11pm and midnight is a different story. During that window the currents would have made it possible for the prisoners to reach Horseshoe Bay at the north end of the Golden Gate Bridge. Those same currents would have also carried debris – like an abandoned paddle – to Angel Island – right where the paddle was recovered in 1962. See the best and worst case scenarios on the videos of their models can be found here and here.
Though this does not determine precisely what happened, and in many ways matches up with the Mythbusters test, these results provide important deeper insight into the critical timing and tight window for survival that the three prisoners faced. To conduct this kind of study Mythbusters-style would have taken ~800 rafts made of ~44,000 raincoats.
In addition to questions about sea-level rise, or related questions about prison escapes, scientists are using models to get a glimpse into other highly complicated and difficult-to-test systems.
Consider airplanes. The materials used to build them are carefully tested to make sure that they will keep us as safe as possible in the air. But many of these planes now have parts that are decades old and have been exposed to the stress and conditions of flying many thousands of times. Scientists try to test these materials as they age to make sure that the changes will still keep us safe. But those scientists also know that many of the processes that affect aluminum after that amount of time actually begin at scale of atoms that make up the aluminum alloy itself.
As big as airplanes are, their strength and durability can come down to their smallest atoms (Credit: Lars Söderström)
It is simply not possible to check every part of every plane for damage at the atomic scale before every flight. It is not even possible to check for that kind of damage on an entire plane and be able to fly it again, so researchers use models to find out the most important places to check and determine when there would most likely be a problem. Using models, researchers can simulate the changes that could happen at the atomic scale over days, weeks, or even years.
You can easily see for yourself how quickly models become useful for trying to understand something that you might not be able to measure. Think about dropping a basketball, measuring the first bounce, and comparing it to the height from which you originally dropped the ball. You could probably measure this from one foot or two feet, or even six feet. Maybe you could even do ten feet if you had a ladder or a high staircase.
But what if you wanted to know about dropping it from 80 feet? Even if you could find a building that tall to drop it from, how would you accurately measure the bounce? What about 150 feet? Or 200? Very quickly the question becomes impractical, but not impossible.
Think about how you could make your own model. Start with the measurements you can make – at 1, 2, 3, 4, and 5 feet – and make a graph. Does it make a clear line? Is there a curve? Can you tell? Add more measurements – 1.5 feet, 2.5 feet, maybe even up to 8 feet with some help. Is the pattern getting clearer? See what you can get as an estimate for what that first bounce would look like dropping the basketball from 20 feet. What do you think is holding your model back? Might there be a height limit where the behavior of a dropping bastekball might change? Why might this be?
Remember that you use models to understand systems around you all of the time, but with careful measurements and a lot of data these models can become sophisticated enough to make predictions about important events, like earthquakes or the spread of the flu through your neighborhood. Start to look for the models you use every day, and you might be surprised to see how many you find.
Sources:
Sumner, T. (2014, December 17) Alcatraz escapees could have made it safely to shore. Retrieved from https://www.sciencenews.org/article/alcatraz-escapees-could-have-made-it-safely-shore
F. Baart et al. Reconstructing the Alcatraz escape. American Geophysical Union annual fall meeting, San Francisco, December 16, 2014. American Geophysical Union. (2014) The 1962 Alcatraz escape was possible [Press Release]. Retrieved from http://fallmeeting.agu.org/2014/press-item/press-release-the-1962-alcatraz-escape-was-possible/
American Geophysical Union. (2014) The 1962 Alcatraz escape was possible [Press Release]. Retrieved from http://fallmeeting.agu.org/2014/press-item/press-release-the-1962-alcatraz-escape-was-possible/
Baker, K.L. & Warner, D.H. (2014) An atomistic investigation into the nature of near threshold fatigue crack growth in aluminum alloys. Engineering Fracture Mechanics. 115 doi:10.1016/j.engfracmech.2013.10.019
ePoster: https://agu.confex.com/agu/fm14/meetingapp.cgi#https://agu.confex.com/data/handout/agu/fm14/Paper_25480_handout_563_0.pdf (With permission from Rolf Hut)
Images:http://commons.wikimedia.org/wiki/File:Bouncing_ball_strobe_edit.jpg?uselang=en-gb
"AA and SAS 767" by Lars Söderström
http://commons.wikimedia.org/wiki/Alcatraz#mediaviewer/File:LocationAlcatraz.svg
http://commons.wikimedia.org/wiki/Alcatraz#mediaviewer/File:Alcatraz_pano_MC.jpg
ePoster: https://agu.confex.com/agu/fm14/meetingapp.cgi#https://agu.confex.com/data/handout/agu/fm14/Paper_25480_handout_563_0.pdf (With permission from Rolf Hut)