1) Movie 1 (:20) This is a view of constant acceleration through a starfield. This headlight effect is how space travel at near-light speeds would appear, contrary to the special effects in Star Trek and Star Wars universes. But in this movie and in reality, C, the speed of light, is not and cannot be exceeded.

2) Movie 2 (:09) The sphere's delayed shadow - cast earlier when it was in a different position . Light reflected off the sphere is Doppler-shifted, appearing a different colour.

3) Movie 3 (:12) In a world where the speed of light is only five meters per second, a flickering streetlamp does not instantly illuminate its surroundings; rather it casts expanding shells of light into space around it.

4) Movie 4 (:09) A flash does not instantly illuminate the interior, but slowly travels through the tram. As the light must travel out and back, the illuminated region moves outward at half the speed of light.

5) Movie 5 (:19) The streetlamp turns on and off. Even though the wall is closer to the streetlamp than the ground, parts of the ground are lit first. To understand this, we must consider not only the distance of the surface to the streetlamp, but also the distance to the eye.
Now, a schematic world where we can track the path of individual photons. As light makes the trip between the lamp, the surface and the eye, the light which follows the shortest path will reach the eye first. As the direct route between lamp and eye is shorter and thus faster, we see the lamp turn on before anything else is lit. The route to the wall is longer, so it appears later.

6) Movie 6 (1:24) We now look at moving objects. A tram moving close to the speed of light displays many effects, becoming distorted, and changing colour and brightness. Its shadow also falls at an unusual angle. The effects of distortion,the Doppler effect and intensity can be separately treated, so for the moment we "enhance" our image, correcting it so only distortion appears. This correction occurs within the large rectangle. The tram appears to have been shortened, sheared (with the two ends no longer perpendicular to the sides), and slightly bent. To explain the shear, we again move to the schematic world. As the tram moves close to the speed of light, it is shortened by the Lorentz contraction. As the back side of the tram is further from us than the front side, the light takes longer to reach us. Thus the light we see at any one time must have left the front and back surfaces of the tram at different times. As the tram is moving at a speed comparable to that of light, this time delay also means that we see the front surface of the bus later and further along the track than the back surface, thus we see a shear. This effect is known as the Terrell rotation, as the degree of contraction and shear combine to the exact proportions that a rotation would produce. However, this effect is dependent on the object appearing small and distant. If we are too close to the object it's different parts will appear rotated by different amounts, sometimes resulting in extreme distortion.

7) Movie 7 (:16) Moving with the tram, the world around us shows the same distortions. This is the Terrell effect. When generalized to an entire view its known as relativistic aberration.
Also, when we move with the tram, it seems to move faster - time dilation at work.

8) Movie 8 (:50) To understand relativistic aberration, consider the ordinary "real" world. When a vehicle moves through rain, to the vehicle the rain seems to fall at an angle. In an analogous process, photons "falling" into the camera appear to come from different angles as the camera moves at different speeds. As the camera moves faster and faster, photons enter it at increasingly steeper angles. This means that things that would
appear behind us if we were in their rest frame are wrapped forward into our field of view. The same, reversed, applies to outgoing photons. This gathering of light into a narrow circle in the direction of travel creates a headlight effect forward and a dimming effect behind.

9) Movie 9 (:15) Terrell rotation or relativistic abberation also explains why the tram appears small as it approaches us, and large as it recedes from us, as seen here in two different views of the tram from the street.

10) Movie 10 (1:19) Accelerating, we see the distortion increasing, and the sun and clouds rotating into our field of view. The rectangle in the center of the screen is a computer correction which leaves out Doppler and intensity effects to improve clarity.
To see what is happening all around us, we use a mercator projection; a map of everything we can see around us. The map is made by "unwrapping" a sphere and stretching the areas at the poles to make the map flat. This is the same kind of common map of the Earth that shows Greenland stretched to the size of South America. This kind of map obviously creates distortions of its own which have nothing to do with relativity. But using this view may help you to understand the abberation effects of relativity.
Accelerating, we can see that objects behind us increase in size. Even though we are moving away from the houses at the end of the street, at the left and right edges, the houses grow larger. The patch of blue sky overhead shrinks to a small circle ahead of us. And the clouds and sun rotate into that small circle, appearing distorted but maintaining their positions in the shrunken scene.

11) Movie 11 (0:49) Returning to the tram we now consider the colour shift. Even at low speeds, ten percent of the speed of light, objects change their colour significantly. Lamp posts ahead look green, but behind they look red. This is the Doppler shift at work.
Just as the direction of motion of photons change when the camera moves, so do the frequencies which we perceive as colour. Objects we move towards appear blueshifted. Objects we move away from appear redshifted. As we go faster, the effect becomes extreme, and we see a rainbow effect as any sharp spectral features pass through the visible band.
This is the cause of red-shift, an observation astronomers made which showed nearly all stars in the universe are moving away from us and each other.

12) Movie 12 (:39) Without colour correction, the world ahead turns blue, and the sun darkens as visible light shifts into ultraviolet and above. This is matched by a reddening behind. A rainbow ring appears in the sky as the blue colour is shifted through the regions of the spectrum our eyes detect as red and green.
We only see light in a narrow range, ROY G BIV, and high speeds can easily shift visible light above or below visible range.
Doppler shift effects are seen again in this mercator projection.Though the distribution of energy in spectra means that the Doppler effect will sometimes make an object look darker, this is not the only effect changing the brightness of the tram.

13) Movie 13 (:40) At high speeds, extreme intensity effects occur, with most parts of the scene too dark or bright to see. Aberration concentrates photons in front and spreads them out behind, so ahead looks bright and behind looks dim.
Time dilation means the shutter of a moving camera is open longer - collecting more light and making the image brighter.
This effect means that moving light sources concentrate along their direction of motion - front and back lights are equal when stationary.
Accelerating without computer correction, relativity effects swiftly overtake us. The scene changes colour and becomes very bright or too dark to make out. At high velocity, the camera is hit by a beam of high energy radiation.

14) Movie 14 (:11) A subtle effect occurs with shadows. The shadow of the moving tram lies at a steep angle compared with that of other objects. Light moves slowly here, so shadows are not instantaneous. The effects of the blocking take time to reach the surface.

15) Movie 15 (:19) As the tram accelerates, electromagnetic radiation enters more and more directly from in front. This effect, when combined with the doppler shift towards shorter wavelengths of higher frequencies, would produce a lethal high intensity beam of gamma-rays. This is another consequence of traveling near the speed of light usually ignored in science fiction.

16) Movie 16 (:20) Here is the same intensity effect shown in mercator projection. Note that any information from the outside world enters through a very restricted kind of porthole.
How would a message carried by laser beam reach the tram ?
How could a message be sent from the tram to the street ?

17 + 18) Movie 17 & 18 (:27) Moving light sources also cast unusual shadows ­ because they cast different parts of the shadows from different positions at different times. Note the shadow's curving shape on the ground. Why does this occur ?
And although of equal intensity, why does the headlight appear brighter than the tail light as seen from above?

19) Movie 19 (:58) These effects can be seen in the real universe. But the real speed of light is very fast, three hundred thousand kilometers per second. Because relativity effects are most pronounced at very high speeds, the real visual effects of relativity must occur on a much larger scale than the simulations you've just seen. For example : light delay in the "light echoes" of exploding stars, the Doppler shift of fast-moving astronomical bodies, and the headlight effect in the incredible brightness of gas jets directed towards us.
Because light is normally so fast, humans do not notice these effects. Someday, it may be possible, though not practical, to build a space ship with today's technology that could travel fast enough to see these effects directly.

Visualising Special Relativity 7 minutes

21) Movie 21 (:49) A trip down a highway without any relativistic effects. Note that we started from rest, and accelerate uniformly. On the left, is an unusual speed limit sign. It shows that c, the speed of light is only one meter per second, or about as fast as a person walks. The speed of light in our universe is very very fast, which is why relativistic effects are much more difficult to observe. These effects, although measuarable at slower speeds with sensitive equipment, really become noticeable at speeds close to the speed of light.
Also note the position and orientation of the structures in the desert. In the next videos , the speeds, accelerations, and positions of objects will be exactly the same, but visual relativistic effects will be added.

22) Movie 22 (:49) Let's look at relativistic rotation. As we accelerate, the angular compression creates an initial impression of backwards motion.
At the top right is the camera speed relative to the scene, given as a decimal fraction of the speed of light. Although acceleration is constant, the number changes less and less as we get closer and closer to c, the speed of light.
The number at bottom left is the gamma factor, the degree of relativistic effects. This number starts at 1 and increases as we approach c.
At bottom right a bird's eye view shows the camera position on the highway.
As we pass the sign, it seems to rotate. This can be viewed as a Terrell rotation, or as angular aberration keeping the sign in our field of view as we pass it. Look at the difference between our actual postion as viewed from above on the lower right, and our apparent position. The back walls of the building are also visible, and extreme distortion is visible on all the objects. The sky shrinks down to the vanishing point.

23) Movie 23 (:49) We now turn on Doppler shifting with aberration. The desert is blueshifted ahead, causing a rainbow effect. As the sky is blueshifted, it drains of visible colour. The opposite happens at the edges of the image, - the sky takes on a reddish hue and the road is drained of colour as the red desert shifts into the infra-red.
Visible light can be shifted out of visible range entirely. If we recede rapidly from an object, its light will be shifted into the infrared, producing "red-shift," an observation astronomers made showing that most galaxies in the universe are moving away from us.
But approaching, light is blueshifted, even into high frequency gamma-rays, very unhealthy for speedy travellers without shielding.


24) Movie 24 (:49) With full relativistic effects the image turns monotone, with objects near the edge of the screen darkened, and the center brightly illuminated.
These three relativity effects combine here to produce a very dangerous beam of high frequency radiation aimed directly at the traveller. Incoming radiation from all directions is rotated more and more to the front, and is doppler shifted to higher and higher frequencies.
And as we speed close to light speed, time frames stretch. A camera shutter set to open for one second on a very fast passing spaceship would take in much more radiation than if it were on the ground next to you, even with other relativity effects ignored.

25) Movie 25 (:48) The Terrell effect can be shown with this cube. Doppler and intensity effects are off. Note the orientation of the cube change. Compare its apparent position with the actual position indicated at the lower right. We see the cube as it was, catching up with photons.
However, these distinctions are meaningless. Even in this universe, nothing exceeds the speed of light, even when bending, so for light to travel in a straight line, it would have to exceed its own speed : impossible. Reality is the distorted cube, and the bird's eye view is from outside this universe.
On the highway, objects rotated more due to our acceleration. Since we move past the cube at a constant speed, rotation is constant. In space flight, effects would also be constant, because spaceships coast more than accelerating by firing rockets.

26) Movie 26 (:48) If we fly through the cube at a constant speed, the structures Terrell rotate independently, seeming to turn the cube inside out. Even when we have exited the back of the cube, aberration keeps most of it in view.
Here's a few questions to think about :
How would this flythrough change if we started from rest and accelerated through the cube ?
Once you are physically past the cube, if you were to shine a laser light ahead, in the direction where you see the cube, where would the beam end up ?
If you were to throw on the brakes and suddenly stop, what would the cube look like ?
And how would it be possible to land on the cube itself ? Note that by the time it appears the cube is closeby, you are completely out the other side.

27) Movie 27 (1:05) Another interesting property of the rotations produced by relativity is that it preserves circles - that is, a sphere will always present a spherical outline to any observer regardless of their relative motion. This is a special property of circles, and does not apply to any other shape.
We see this demonstrated by orbiting a camera around the Earth at a constant high speed. The camera's position can be seen from above in the lower right hand corner of the screen. Though the camera is very close to the surface, aberration wraps the Earth into our forward field of view. But because we are so close to the earth, we can see only a small portion of its surface so small regions seem to bulge out and fill the sphere.
These effects are present even in our real world, although to a much smaller extent because of the great speed of light. Satellites and space shuttles and Global Positioning Systems all must account for these effects.