Newton has proposed inertia for more than 200 years, and the default time and space for the physical world as a whole is fixed。EinsteinIn one sentence, the foundation was drawn: there was no absolute time, no absolute length. Without a complex formula, two assumptions can be made clear。
You can't detect yourself moving in a closed car
Galileo introduced the inertial law in two new sciences in 1638: objects maintain a flat-speed straight-line movement without external force. But what really matters is the second sentence: the reference system for all flat-speed straight-line movements is completely equal. You sit in a sealed, flat-speed, flat-sharp car, throwing balls, measuring circuits, dripping water, and then welding it to the ground. You don't have any physical experiments to determine whether you're still or moving, which is the simplest expression of relativity。
Einstein moved the principle of relativity into electromagnetics in 1905 and hit the hard wall immediately. The vacuum light speedc calculated by the maxwell equation is a fixed value that has nothing to do with the observer speed. However, at newton's galileo velocity, ground-based photometric velocities are c, and the same beam should be measured in the car moving at v-speed. There's a direct contradiction between the two, there's no middle ground. Einstein did not hesitate to directly declare that all inertial system photometric speeds were c at the expense of giving up absolute time and length, and that time and space themselves had to be changed。
Lorenz turns the time into one
And when the paradox emerged, in 1904 the dutch physicist lorenz gave a mathematical way out: if the length of the same pole under different reference systems can be different and the time spacing of the same pair of events can be different, then the light speed can be completely mathematically consistent. This coordinate formula is the lorenz switch. The biggest difference between it and galileo is that time and space no longer operate independently, but are combined into a four-dimensional space structure。
What einstein's paper did in 1905 essentially gave lorenz a clear physical meaning: length contraction and time expansion were not an additional "effect" but an inherent attribute of spatial geometry. A ship that flies 0. 9 times the speed of light, you measure it short, you see its clock slow, and it sees you in turn. Full symmetry, no one special. Plus e=mc2, narrowRelativityThe framework is completely closed。
Something that a physics graduate can introduce
A specific scenario: assuming you're a graduate of physics in 1900, calculus, vector analysis, classical mechanics, electrodynamics, mathematical ability equals more than 140 points in advanced examinations. You don't have to look at einstein's paper, just two hypotheses — vacuum light speeds are the same for all inertial systems, galileo doesn't work — you can launch the lorenz transition, time expansion, length contraction, mass equations. The extrapolation process is a pure algebra operation, which is not superb。
So the real difficulty is not to be deduced, it's to "bold to raise those two assumptions." prior to 1905, absolute time and absolute length were written as default justice in the minds of every physicist, shaking it was tantamount to shaking the foundations of all classical physics. Einstein's breakthrough was a physical instinct, not a mathematical gift. He starts with "relativity must be established and the speed of light must remain the same" and then math naturally changes lorenzo. The choice of a pair is 100 times more difficult than the push formula。
Equivalence equals gravity and acceleration
Narrow relativityJust keep moving. Einstein has spent 10 years since 1907 on this piece of hard bone, "the acceleration is relative." the core is called equivalence: in a closed space, you can't distinguish by any experiment between "self being evenly accelerated" and "attractive to a mass object." because the inertia and gravity generated by acceleration are mathematically the same thing, the external expression is that inertia is the mass of gravity. This principle binds gravity and temporal geometry directly together。
The principle of equivalence forces a hard conclusion: gravity is not the force that newton calls it, but the geometry of time and space bends. You're standing on the earth feeling dragged down, and it's the earth that bends the space around, and you're just taking the "most straight" path in the sky, and you're doing it in the outer flat reference system. So..Broad relativityThe equation describes not force, but quality tells how time and space bend and how the substance moves。
Space station weight loss is not the disappearance of gravity
Take the example of iss. It operates around the earth at a rate of approximately 7. 7 km/s and has a heart acceleration of about 9 m/s2, almost as large as the earth's gravity acceleration. You feel completely weightless standing in it, but the earth is gravitational, and it's just used to provide the power of the circle. Gravity pulls down, inertia throws out, and both are perfectly offset. Thus, although a typical non-inertial reference system within the station, physical law is fully consistent with inertia, which is the most intuitive application of the equivalent principle。
In september 2015, two ligo detectors in livingstone, louisiana, and hanford, washington, caught a gravitational wave signal simultaneously. It was a combination of two black holes of about 36 times the mass of the sun over 1. 3 billion light years, and it took 4. 9 billion years for the space and space to reach earth. The signal coincides with the quantitative prediction of broad relativity to several decimal points. Gravity waves are no longer just the equations on paper, but the physical reality that can be measured in terms of arrival times。
The relativity is really hard to choose
A lot of cope talks about relativity as "a scary formula," but the real hard part is the first step: how do you propose "all inertial systems equal" and "time can bend"? Prior to 1905, the entire physics community defaulted on absolute time, shaking it was tantamount to shaking the foundations of newton mechanics. Einstein's breakthrough was to define new principles and then make math fit. If you're leading lorenz to change or einstein's equation, you can follow someone with enough math; but the original selection of the hypothesis is a physical instinct, not a brush。
To sum up, relativity is the choice of a principle of relativity under certain conditions, and then to abandon the notion of space and time that you thought was unshakeable. A narrow waiver of absolute time and duration and a broad waiver of space and time must be flat. Newton's inertia law is the exception to the principle of relativity at low-speed limits, not the opposite. The progress of physics has never been to throw away the old theory as a whole, but rather to paint the applicable boundary, which should be the same and not the same。
You've got gps on satellite every day, without correcting relativistic deviations, which drift a dozen kilometres a day. Which day-to-day technology around you actually relies on relativity? The comment section said that if there was something to be gained, the words were passed on to the fellow student who was still at galileo。
