> Funny - you could say the same about physics. For example, knowing that the coming car may kill a person causes the human behaviour to change, namely the driver will stop the car. Does that invalidate Newton's laws?
The difference is that whether a person will try to move out of the way of an oncoming car is not considered within the domain of physics (so them using their knowledge of physics to predict that a car is a danger may change their behavior, but not the accuracy of what physics predicts within its domain), but whether or not a person will try to move their money out of the path of a predicted stock market collapse is within the domain of economics.
This doesn't actually make empiricism any less applicable to economics, but it does compound problems in the empirical study of economics.
No, it's an artificial distinction (or perhaps better would be to say, there is an artificial distinction where you decided that physics is not a social science). In both cases, you can analyze two scenarios:
1. Car continues and hits the person / investor won't move money out before stock market crashes
2. Car is stopped / investor will move the money out
In both cases, the physics or economics is no less applicable whatever the circumstances of the actual decision. And just like physics cannot tell you whether the car stops, economics cannot tell you whether investors will actually move the money out. But what economics can tell you, under certain assumptions, say, investors want to make money with this and this horizon, whether or not are they likely to move out.
Let me give another example. Water flows downhill due to gravity. Yet, people can decide to build water pump and aqueduct to get water uphill. In doing so, they didn't break any physical laws. But if you ignore the pump, it may seem that the water flow downhill anymore and so the laws are incorrect. What happened is that now our model of the situation should include the pump, and within the expanded model, physical laws are again preserved.
Similarly for instance, if the society decides to regulate markets, the behaviour of the people can be changed, but they don't necessarily have to break some universal economic law. The new behaviour can have a perfect economic explanation, it's just that the frame of the model changed.
It seems that this "infinite regress" confusion (also called Lucas critique, if I am not mistaken) is caused by ignoring the fact that every model of reality only includes a portion of it and is never a perfect description (for example we ignore the physics of human brain when we model the car hitting the pedestrian).
Also, you should note there are situations where knowing more doesn't actually change the behaviour (under assumption of certain rationality) - for example, getting to know the exact odds of casino wins won't entice me to play.
The difference is that whether a person will try to move out of the way of an oncoming car is not considered within the domain of physics (so them using their knowledge of physics to predict that a car is a danger may change their behavior, but not the accuracy of what physics predicts within its domain), but whether or not a person will try to move their money out of the path of a predicted stock market collapse is within the domain of economics.
This doesn't actually make empiricism any less applicable to economics, but it does compound problems in the empirical study of economics.