Presentation on theme: "Philosophy 024: Big Ideas Prof. Robert DiSalle Talbot College 408, 519-661-2111 x85763 Office Hours: Monday and Wednesday."— Presentation transcript:
Philosophy 024: Big Ideas Prof. Robert DiSalle Talbot College 408, x85763 Office Hours: Monday and Wednesday 12-2 PM Course Website:
“Scientific Philosophy”, a.k.a. Logical Empiricism: In general, statements can either be true or false. If true, this means: If it is a logical or mathematical truth, it can be logically derived from first principles. If it is a statement about what there is in the real world, or any matter of empirical fact, it can be verified by some observations. If false, this means either that it is logically contradictory, or that it is contradicted by the facts.
Verification and Meaning: A statement that cannot be verified by any empirical observation or logical reasoning, even in principle, is neither true nor false. It is completely meaningless. Example: “Nothing nothings” is neither true nor false. It simply has no cognitive content. Whatever content it might have is emotional rather than cognitive. (It is not a direct statement about any state of affairs. It is an indirect statement about the emotional state of the speaker.)
Albert Einstein ( ) “On the electrodynamics of moving bodies” (1905) “The foundation of the general theory of relativity” (1916)
Einstein and the philosophers: What Einstein did was not merely to propose a theory with powerful philosophical implications (e.g. the relativity of space, time, and motion). He actually created his theories by applying philosophical analysis to the fundamental concepts of physics. His theory of time is not a hypothesis about time, but a philosophical analysis of the concepts involved in our thinking about time and how we measure it. Relativity reveals that our usual notions of time are based on concepts that have never been clearly defined.
Heidegger on the notion of time: Temporality gets experienced in a phenomenally primordial way in Dasein’s authentic Being-a-whole, in the phenomenon of anticipatory resoluteness. If temporality makes itself known primordially in this, then we may suppose that the temporality of anticipatory resoluteness is a distinctive mode of temporality. (Being and Time, 1927)
Einstein on simultaneity (1917): We encounter the same difficulty with all physical statements in which the conception " simultaneous " plays a part. The concept does not exist for the physicist until he has the possibility of discovering whether or not it is fulfilled in an actual case. We thus require a definition of simultaneity such that this definition supplies us with the method by means of which, in the present case, he can decide by experiment whether or not both the lightning strokes occurred simultaneously. As long as this requirement is not satisfied, I allow myself to be deceived as a physicist (and of course the same applies if I am not a physicist), when I imagine that I am able to attach a meaning to the statement of simultaneity.
Simultaneity: For any events A and B, one of the following must be true: A happened before B, or, B happened before A, or, A and B happened at the same time. “Here and now,” a certain event happens. “Now,” at other places, other events are happening. “Here,” before and later, other events have happened or will happen. What happens before “now” is already determined. What happens after “now” is still indeterminate.
The present (“now”) time space The future The past Events that can still be influenced by what you do now, but that cannot influence what is happening now Events that can influence what happens now, but that cannot be influenced by anything you do now here and now The “causal structure” of spacetime
time space Space at time t “Laplacian determinism”: if you knew the positions and momenta of all particles at a given time t, you could deduce their trajectories for the entire future or past.
time space Events that can still be influenced by what you do now, but that cannot influence what is happening now: the “future light cone” of p Events that can influence what happens now, but that cannot be influenced by anything you do now: the “past light cone” of p p What if you couldn’t travel faster than light? Causally inaccessible to p
time space p If you can’t travel faster than light, then what’s happening “now” can only influence you later. “now”
What is simultaneous for a bat?
time space The bat in spacetime
time space Visual perception in spacetime
If you can’t travel faster than light, then you have to determine when a distant event happened by taking account of the distance and the velocity of light. If you observe two events at the same time, and they happened at the same distance from you, then they must have happened at the same time. If events happen simultaneously at different distances from you, then you won’t observe them at the same time. To determine that they were simultaneous you have to calculate by the velocity of light and the distance. As long as you are at rest there should be no ambiguity.
If you are (say) one light-year from some stationary source, then when you receive a signal you know that it was sent one year ago. But if you are moving, then you have to consider your own velocity as well as the velocity of light, and calculate the difference. c-v = ?
If light propagation is isotropic, then light from the explosion goes equal distances in equal times, and reaches equidistant points at the same time.
The same thing, in space-time time space
Einstein on the train ( Dramatization)
t2t2 t1t1 F1F1 F2F2 t-t- t+t+
Einstein: The invariance of the velocity of light is real. Simultaneity is relative: whether two events occur at the same time depends on the frame of reference. Therefore the Lorentz contraction and time- dilatation are mere frame- dependent appearances. Lorentz: The contraction and dilatation are real. Simultaneity is absolute: it is an objective fact whether two events occur at the same time. Therefore the invariance of the velocity of light must be mere appearance. Two views of the electrodynamics of moving bodies: