Mood Brightener: ...more from Stay Homas. (Confination XII)

 

Fields:

So here's the core question: Why do we think some exists if we can't see it, touch it, smell it, or feel it? Generally this is the definition of something which does NOT exist. On the other hand we also have a human experience that most things that happen in life have something which causes that effect. The idea of cause and effect is built into our lives at a very fundamental level. To the extent that we sometimes invent a cause to avoid violating this idea. This is what we are exploring for the next day or so.

Gravity:

Sometimes we are so familiar with an experience that we don't actually step back and notice how surprising it is at some level. Gravity is an example of this. The effect of this thing we call gravity has never been absent from our lives so we may not think about it much but let's start down the road of examining it a little more closely (this is an example of Tim Minchin's advise to examine your beliefs closely!)

From an experimental point of view how do you know that there is gravity?

Class Discussion:

We talked about a number of ideas. The most simple of which was just to take a ball or a rock to the location and let go. If it drops then there is gravity. We then talked about the International Space Station which is so close to earth there must be gravity and yet when they let go of a ball is certainly don't drop. What? At that point I shared this OK GO video which I include here in case you're looking for it.

 

 

Consider this thought experiment: I make you a nice safe container with no windows and I put you out in space for a moment. What does it feel like in your container? Why does this happen? Is that different than you would feel if I took you (in your container) and dropped you from a high place (don't worry, we'll catch you safely)?

This thought experiment is intended to suggest that we don't 'feel' gravity. We 'feel' something when there is no gravity that is very similar to what we feel if the only thing going on is gravity. A way of thinking about this to ask whether you feel gravity pulling you down at this moment or do you just feel the chair holding you up?

It seems likely that we will arrive at a place where we can determine if there is gravity at a point by placing a stationary physical object like a ball there and seeing if it 'falls'. At least here on earth this appears to work.

Can you find a place in your home where you could put an object and it would not be subject to gravity? Apply our test and see if there are any caveats we need to add to this test. Now we have a test that seems to be useful in determining if there is gravity in some particular place.

Next Question:

Is there 'gravity' at some location if there is no object there to feel it? I know, this is a little like the tree falling in the woods thing but it's not really the same. If you put a physical object there will it fall? Why? So, doesn't that mean something is already there? But what? Is there any other way of detecting 'it' than to put an object there?

After many years of discussion a solution that seems to work is to imagine that there must be something at every location that is just waiting to tell us to fall. We don't have to be there to experience it, it just is. We call this invisible thing a field. A gravitational field in this case. It is invisible to us except when we place a physical object there. If we use the same object to detect the field we can determine the characteristics of the field by examining differences in it's effect on the object. How might the object tell us the field is stronger or weaker (you have to decide what you want to mean by those adjectives)? Can the field depend on the object we're using to detect it? If the object moves in different directions when placed at two locations what does that mean? What do you imagine is the same or different about this field if we are on the moon? Is there a source for this field?

This is what physics means when it talks about the gravitational field of the earth. A mysterious thing that has a clear direction and intensity at every point in space. Separate from the whole bending of space-time thing which is another discussion.

Consistency and Science:

As we talked about earlier with models one emphasis was on the evolution of those models as they are continually tested. One important kind of testing is verification of previous tests. Models are more believable if they yield the same result under the same circumstances. If I drop a rock and it arrives at the ground in the same amount of time every time I do the test then my model for gravity is more robust.

Reproducibility is very important to model building. If you are intrigued by such things here is link to a recent Gizmodo article noting difficulties in reproducing results for a number of scientific papers. One can appropriately ask whether difficulties reproducing the results of scientific studies is a 'bug' or a 'feature' of the scientific model building process.

What are your thoughts?

I would want you to understand that the actual expectation is that the original publisher has done everything they could think of to make sure their results are consistent and reproducible. If they are the first folks to see the particular effect they absolutely expect that others will also try to reproduce the experiment. Only when a result is consistently observed in a set of circumstances that are understood is the new and improved model accepted. As you will recall this is the model building process we discusses as an endless cycle of testing and modification. With that in mind, integrity in science means providing enough explanation in your publications for others to reproduce your experiment and come to conclusions consistent with their data.

A field is a concept that has become widely used to describe a range of phenomena where the cause of an observed effect is mysterious or unclear. This is certainly true of gravity and other fields we will discuss. The fields we are talking about here are ones where the field and it's effects in the world are consistent and reliable across a wide range of reasonably well understood conditions. Fields which do not meet this condition may eventually be shown to be a reliable model but for the time being are not included in scientific models.

Consistency and COVID:

I would be totally remiss if I didn't tie this discussion to our current national circumstances. The difficulty with our situation is that we don't have the time that is normally required to test our models for the transmission and treatment of COVID sufficiently. We are in the middle of a rapid development of our models for how this virus and disease work. So what should we do when the model is evolving rapidly?

The cholorquine (malaria drug) discussion is a excellent case in point. There was an early study of a few patients that suggested that there may be some potential benefits to this drug for hospitalized COVID patients. There are clear known risks to this medication so it is important that there be data to help weigh the benefits against. Since then multiple studies have found little or no impact from this drug in helping seriously ill COVID patients. Other drugs have been found to be of significant help. For patients with mild to moderate symptoms (not thought to be at risk of death) there is appears to be a small positive effect from chloroquine. In a few years we will have a much better picture but for now how will you make the assessment of what to do? If humans are rational creatures (which we largely are not) the data at this time would lead them to skip the cholorquine as having a small impact on recovery times for patients not likely to die anyway and a real, though small (0.1% ish), risk of serious cardiac and neurological problems. This is tough stuff for us as humans and when we are uncertain and in a burry we tend, based on reproduced research, to behave less rationally rather than more rationally.

Other Fields:

In physics there are currently only 4 known fields. Admittedly one of them we often think of as two related fields. Those 4 are gravity, electromagnetism, strong, and weak. Electromagnetism we often think of as the combination of electric fields and magnetic fields but we have found them to be two sides of the same coin. Gravity we all have lots of experience with and probably we have some sense of the electric and magnetic fields. Strong and Weak forces (and their fields) only occur in the nuclei of atoms and so we have no experience with them. We will talk more next time about electric and magnetic fields which are very common in our world. We will leave the discussion of the fields associated with the strong and weak forces for another class.

If you want to explore more here is one of the better discussions I have seen about fields from a stackexchange thread.

Quantum Fields:

Quantum fields are a whole different kettle of fish. One significant challenge for understanding quantum fields is that while their effects are reproducible what is reproduced is a statistical outcome not a consistent effect. If you hammer your thumb 10% of the times you pick up and use a hammer that's a clear and reproducible result and the model is good but the idea of cause and effect is more blurry. We wouldn't even be talking about these strange fields except that they predict and describe, in a totally reproducible way, various processes at an atomic level that we have no other way to describe. That makes them as real as it gets in physics. On the other hand, the strangeness of what these fields say about the world has contibuted to the deaths of several prominent physicists a century ago. Walk carefully in the world of the quantum.

Assignment Breadcrumb Reading: Bb Quiz

How Many Fields:

How many physical fields do physicists have reproducible evidence for at this time?

Before Next Class:

Assignment HW: Bb Quiz

Detecting a Magnetic Field:

As we discussed we need some object to detect the presence of a field. For gravity that object is a mass of some kind (a physical object). What would you use to detect a magnetic field?

Assignment HW: Bb Assignment

Many Labs 2:

Read this article from The Scientist (2018) which describes the broad outcomes of an effort to replicate a number of important earlier results from psychology. Based on your reading of this article how will you think about the next newsfeed article that explains why you act the way you do? Try to damp down your natural cynicism as you answer this:)

Looking Ahead:

Look ahead to the next Breadcrumb: Fields II

Assignment Breadcrumb Reading: Bb Quiz

Fading Away:

How do various fields die away as we get further from the source? You will be choosing multiple answers from a list.