An object moving past an arbitrary point used for measurement. In the objects stationary frame the arrow is doing the moving, and in the arrows frame the object is doing the moving. That is, the distance between is just the length, and the time between is how long it takes for the measuring point to traverse that distance. That is, the events happen in the same place, but at different times given by how long it takes the object now L M long to pass. Pingback: Q: How do velocities add? Pingback: Q: Do time and distance exist in a completely empty universe?
It would be red shifted. Pingback: Q: According to relativity, things get more massive the faster they move.
If something were moving fast enough, would it become a black hole? Spaceman heading to star 10 light years away, as measured by Ground Control on Earth. Speed attained is close to the that of light. Does the actual distance contract that the spaceman has to travel? So, does the period taken for the Spaceman to reach the 10 light year away star distance divided by speed , now take less time, than had been calculated prior to the journey due to the shorter distance now being experienced as a consequence of length contraction or does time dilation result in the actual journey time equalling the calculation prior to setting off?
Paul Quinn Length contraction and time dilation are two sides of the same coin. The space man would say that the distance was shorter and that his watch ran normally length contraction. I can understand that we observe things and things will look different to different people based on movement and their location.
And I love the maths to work out what length an object will appear as. But just because of the order of events may be screw-if and B fore A, to me does not change the facts that the pole is still shorter than the barn. In fact I noticed you talk about the pole being longer then in your next paragraph after you say its real we jump into being shorter with length contraction. SO to me you used an example to prove the opposite. And why is it real.
If I pressed Pause on the universe at that exact moment as the pole vaulter and the rod stayed in place and I walked around it. I do not believe it would be longer than the barn. But was only being observed longer than the barn. I had this story. If a space ship at light speed travelled 25 light years to earth. It wold take 25 years for the light of that event to arrive and at the ship being 24 lights years out, would take 24 light years to arrive and so on.
So when it gets to earth, assuming you could see it all. The light from all events would arrive all at once. Well truth is the ship is still the same length, but all we are seeing is the effect of light bringing the image to us out of event. Maths can be used to work out length dilation based on an observation, but I think it is being used the wrong way around. Objects look longer at speed, and we use their speed and reverse engineer the length to work out the actual length of the object.
But I could be wrong and everyone contradicts the way I see it, but I am yet to be convinced. Can you help. The effect you described at the end, with a ship approaching at the speed of light, is a strictly visual effect. Pingback: Q: In relativity, length contracts at high speeds. Is it distance or space or is there even a difference? In the pole vaulter example, I can see why the pole vaulter views the pole as longer than the barn because they are approaching the front of the pole and moving away from the back of the pole.
In the train track example the observer who was stationary relative to the lightning strikes saw them happen at the exact same time not one before the other. Conor The briefly shut barn doors take the place of the lightning strikes, not the ends of the pole passing through the doors.
All in all, these effects will make a rapidly moving object, such as the Enterprise , appear nothing like it does at rest. The idea of length contraction was postulated by the Irish theoretical physicist George FitzGerald in and by the Dutch theorist Hendrik Lorentz in It was only in that Albert Einstein cut through the confusion when he published his special theory of relativity. It did away with the aether altogether and proposed two postulates. The second postulate states that an observer in any inertial reference frame will measure the speed of light in a vacuum to be the same.
From his theory, Einstein derived length contraction as well as time dilation, the equivalence of mass and energy, and more. Paradoxically, an observer on that train will measure the first as shortened by the same factor. Length contraction has never been directly measured. But its effects show up in the magnetic force that acts between parallel, current-carrying wires. Phys 29 and Eur. What both Einstein and Lorentz overlooked, however, is the fact that the photons may have been emitted by the object at a different time, especially if the object is large.
For an observer looking head-on, two sides would now be visible but not seen to be of equal area. The moving cube will thus look the same as an undistorted, rotated, non-relativistic cube of length L. Lost in history Over the years, few people paid much attention to observing Lorentz contraction.
Concerning the appearance of a moving rod to an observer, his work was unfortunately largely overlooked. He showed bicycles as simply shortened in the direction they are travelling, instead of being distorted and elongated when approaching an observer, or contracting as they receded into the distance.
Researchers only properly started to take notice of the practicalities of observing Lorentz contraction when Terrell published an internal Los Alamos article in about the effect, followed two years later by a paper in the Physical Review 4. Like Terrell, Weisskopf also noted an earlier article by the British mathematical physicist Roger Penrose , in which he analysed the appearance of a relativistically moving sphere.
In his paper on special relativity, Einstein had said that such a sphere would look like an ellipsoid, contracted in the direction of motion. But Penrose reckoned that the object would still be spherical, albeit rotated. The eye or lens sees images from photons that strike it simultaneously, but these photons — especially for a rapidly moving object — do not leave the object simultaneously.
Surprisingly enough, in certain circumstances this difference exactly cancels the Lorentz length contraction and the moving object appears rotated. To appreciate why Lorentz contraction disappears for an object moving at relativistic speeds, Peter Signell from Michigan State University has considered the simple case of a cube moving left to right when viewed head-on see figure 1, above.
Of course, to fully understand the appearance of a rapidly moving object, you have to calculate the geometry not only for arbitrary viewing angles but also for arbitrary distances, velocities and sizes i. In each animation a spaceship is moving past Earth at a high speed.
The spaceship would be measured to be feet in length when at rest relative to the observer. Spaceship Moving at the Note that the length contraction is only significant when the object is moving at relativistic speeds - i. Furthermore, note that the contraction only occurs in the dimension of the object's motion.
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