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Physics 11 Advanced Special to General Special Relativity is all about inertial reference frames. Example of an Inertial reference frame: Deep Space ○ No Earth ○ Far from sources of gravity ○ Very lonely place where we like to do physics Properties of Non-Inertial Frames No forces acting on it Constant velocity If our space-physicist let go of an object without exerting a force on it, the object just floats Boring Making it Non-interial What happens if this person is in a room in space that has a rocket on it? ○ A “rocket room” if you will What happens we they let go of the open bottle? Making it Non-interial What happens if this person is in a room in space that has a rocket on it? ○ A “rocket room” if you will What happens we they let go of the open bottle? No force on bottle We are pushed up We perceive Object “falling” The Equivalence Principle Einstein’s radical idea was to say the following: “A homogeneous gravitational field is completely equivalent to a uniformly accelerated reference frame” Sure, but what does this mean? The physics in a gravitational field should be the same as the physics of an accelerating reference frame. These people have no Idea… Non-inertial Reference Frame What we perceive is a sort of “artificial” gravity Is it “artificial”? Newton’s Gravity Newton gave us a model of gravity between two objects that states the force of gravity depends on the mass of the two objects …That’s fine. (More on this in Grade 12) but consider the following…. Newton vs. Einstein Newton states that an object must have mass to be affected by gravity Einstein disagrees. Einstein Says… …because of the equivalence principle, the force of gravity is just the ground acclerating towards us If we are accelerating, how do we see a pulse of light? Einstein says MASSLESS light is affected by gravity So who is Right? Turns out that light is bent by gravitational fields ○ Einstein 1: Newton 0 Effect known as “Gravitational Lensing” First observed during a solar eclipse in 1905 Shift in apparent position of a star in the sky Gravitational Lensing 1905 eclipse Deep space Galaxies Light and Space-time It is important to note here, that light still travels in a straight line in space-time. It appears to bend because space-time is warped Light and Gravity Consider light as it leaves a massive body (the sun) GR tells us that time warps/bends as you approach a massive body SR tells us that the speed of light must be constant So like a rocket on earth, light needs to escape the pull of gravity Decrease energy of photons, lower frequency E hf Changing space-time should changes frequency and wavelength of light c f Everything suggests a frequency change of light Black Holes If space-time is warped enough, light emitted from a body will not escape the field. This is a ‘Black hole’ At the very edge of the black hole, space-time is warped just enough that light orbits the mass. This radius tells us how large the ‘black’ part of the black hole is. ○ “Schwarzschild Radius” More Alice and Bob Problems ○ A 656nm photon is emitted from a star and observed on earth to be red shifted by 15nm. How fast is the star moving away from the earth? ○ Two musicians play a note of 440Hz; one musician is at rest while the other is moving to the right. If a beat frequency of 5Hz is heard, how fast is the second musician moving wrt to the first?