Special Relativity and the Myth of the Passive Observer

2020-10-26 14:32:57.000 – Nate Iannuccillo, Weather Observer/Education Specialist

 

A couple weeks ago, the summit experienced what ended up being the most intense thunderstorm that I’ve personally witnessed in the White Mountains. For at least one observation, we even coded “Continuous Lightning” in our METAR (meteorological aviation report). This is defined as observed lightning occurring 6 times per minute. The storm was particularly fierce with a tornado warning going out for Coos County, and the summit even got struck by lightning three times over the course of an hour.

 

After the lightning subsided, I got to thinking about the day’s events, and my thoughts led to some interesting reflections. As I considered the lightning strikes on the summit, I was reminded of a classic physics scenario used to help explain Albert Einstein’s special theory of relativity.

 

The example goes something like this…

 

You find yourself on a high-speed train, traveling through a thunderstorm. As the train is speeding through the countryside, you see the front of the train get struck by lightning immediately followed by the rear of the train also getting struck shortly after. As an observer on the train, you witness these strikes occurring at two separate times.

 

Simultaneously, a person standing still in the countryside also watches the train go by, and also manages to see both lightning strikes. However, in this case, this person observes both lightning strikes occurring at the same time.

How can this be? And whose observations are correct?

 

Special relativity tells us that they’re both correct as long as we assume that the speed of light is constant. This then forces us to consider the reference frame of the observer in relation to the speed of light.

 

If the speed of light is constant at approximately 3×108 m/s, then we also know that the visible world we perceive is always a function of the time it takes light to reach us. In doing so, we can recognize that everything we see and perceive has a certain time attached to it. This is what is meant by the space time continuum.

 

This becomes especially important when studying things on really small and really large scales. For example, we measure the distance of deep space objects based on the time it takes light to reach us. This is what is meant by a “light year”; the distance light travels in one year. For example, the andromeda galaxy, an object we can see with the naked eye during favorable atmospheric conditions, is approximately 2.5 million light-years away. This means that the light we’re seeing from this galaxy is around 2.5 million years old, some of oldest light we can see unaided. I find that pretty incredible!

 

Recognizing the relationship between time and space, we can see how important it is to take into account the motion of the observer relative to the speed of light. This is what special relativity is asking us to do, to always consider the motion of the observer relative to the speed of light. In doing so, we can see that time passes slower for objects in motion. Imagine yourself moving away from the andromeda galaxy. The time it takes for the light to reach you will be different from someone else moving at a different velocity. And so we see how important it is to consider the reference frame of the observer.

Returning to our example with the highspeed train, I think we can now see, when considering the different reference frames, that these events can and do happen at different times for different observers.

 

After mulling this over, I eventually realized that its significance has everything to do with the fact that as an observer, special relativity proves that at the largest and smallest scales, we cannot observe anything without somehow changing it. Essentially, the observer is always part of the picture. Often times, as scientists, we like to think that we can remain detached, simply studying things “as they are”, but relativity checks this attitude.

Relativity means that we have to see and interpret the world through our own frame of reference. In doing so, we have first become aware of our bias as observers, and relativity highlights this quite well.

 

While relativity factors in adjustments primarily for large and small scales (think particle physics, astrophysics etc.) that are generally outside the scope of my job here at the observatory, I find myself questioning my own role on a more philosophical level. What does it mean to be an observer? What is the frame of reference that I’m constantly living in? What kinds of biases do I display in my own frame of reference each and every day? I’m not just talking about my job title; I’m talking about how special relativity has caused me to continually examine my role as a biased observer in a dynamic world...

 

Nate Iannuccillo, Weather Observer/Education Specialist

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