Disney in Paris

Each Disney park is a bit different, which makes it fun to visit them all. Disneyland Resort Paris emphasises the European roots of fairy tales, starting with the castle.

Tomorrowland has become Discoveryland, inspired by France's native son Jules Verne. The decor is 19th century steampunk, full of brass and rivets. A redesigned Space Mountain blasts you off in a cannon like FROM THE EARTH TO THE MOON. The Hyperion airship from Disney's ISLAND AT THE TOP OF THE WORLD was inspired by the French Lebaudy airships of 100 years ago.

Not everything in Discoveryland is steampunk-- this X-wing fighter decorates the Star Tours outpost. There is no monorail, but the park has a rail station served by TGV and RER from Paris. In Europe the dream of superfast trains has already come true. NEXT: Mysteries of the Nautilus.

Ole Roemer and the Observatoire

For the "Invisible Universe" conference, Paris Observatory was location of a welcoming ceremony Sunday and a farewell cocktail Friday. The grounds contain a line marking the Prime Meridian. For many years navigators disagreed whether to measure longitude from here or Greenwich. Eventually Britain's mastery of the seas led the world to adopt the Greenwich Observatory as Prime Meridian.

For centuries scientists disagreed whether light had a finite speed at all. Aristotle and even Kepler believed that light travelled instantaneously. This was once a reasonable assumption, for light travels so fast that to most observers it seems instantaneous. Galileo suggested stationing observers on distant hilltops with lanterns to determine if there was a time delay. This would have been difficult for Galileo, because a good clock had not been invented!

Young astronomer Ole Roemer came to work at this observatory in 1672, working for Dominic Cassini. At the time there was an anomaly in observations of the Galilean moon Io. The time when the moon emerged from behind Jupiter appeared strangely delayed. Cassini ordered his staff to make more precise observations to resolve the puzzle. Roemer realized that, if light had a finite speed it would take time to cross Io's orbit, delaying the moon's apparent emergence. Using data from this observatory, Roemer was first to measure the speed of light.

Having made a great discovery, Roemer was unable to convince his elders. Cassini was a distinguished astronomer in his own right, but believed that light travelled instantaneously. Finally in 1675 Roemer was bold enough to present the results on his own. He also predicted that on November 9, 1676 Io would appear at 5:35:45 rather than 5:25:45 as astronomers had calculated. Though Roemer's prediction was correct, Cassini and others who followed him insisted that there was no speed of light. It was 50 years before other experiments proved that light had a finite speed.

As scientists once believed that light travelled instantaneously, today they say that its speed is finite but fixed. This was once a reasonable assumption, for channge in c is so slow that to most observers it seems constant. Observations of high-redshift supernovae indicate that light has slowed over time. This result is corroborated by measurements of solar luminosity and light signals reflected from Earth's moon. We will not have to wait 50 years to prove that the speed of light is slowing.

Lumiere

As promised, photos from Paris and the "Invisible Universe" meeting. Here is the view from UNESCO headquarters, the conference site. The parade ground lies in front of Ecole Militaire, where French officers are trained.

Eiffel Tower from Champ Du Mars. In 1783 the Montgolfier Brothers launched their first manned balloon from this site. Since radios were introduced a century ago, the tower has been a natural site for transmitting antennas. Signals radiate outward at the speed of light. Space and Time are one phenomenon, also related by the speed of light. If an event is outside this expanding sphere, its separation is spacelike-the tower's signal is too late to affect that event. If you are "within the sound of my voice" our separation is timelike, literally a matter of time. From this simple principle (without a fixed c) one can derive all the equations of the Lorentz tranformation.

Wednesday the scientists took a boat tour down the Seine and around Ile St. Louis. A long day of meetings leaves one worse for wear. On a hot Summer night crowds gathered around the riverbanks. In the cafe atmosphere of Paris, scientists discussed new ideas like a changing speed of light.

MOND

The UNESCO palace, site of the "Invisible Universe" conference, is across from Ecole Militaire and within sight of the Eiffel Tower. Today there was time for a visit to the War Museum and Napoleon's tomb between talks. Last night I shared a table with Mordecai Milgrom and his wife. This afternoon Milgrom gave a 45-minute talk on MOND, modified Newtonian gravity.

While scientists since Fritz Zwicky and Vera Rubin have looked for "dark matter," Mordecai and colleagues have been developing MOND as an alternative for the last 25 years. Since DM has never been directly observed, the field is open to alternatives. He claims that MOND can match the predictions of DM. The theory is far from complete, Milgrom admits, but today he was able to present before an international audience.

Though they sound similiar, "dark matter" and "dark energy" would be quite different if they both existed. One would attract and the other repel. They possibly share the quality of being misnamed. DM could be made of Black Holes that have never been matter at all. DE can be explained by a changing speed of light. They are both inferences that have never been directly observed.

One of Mordecai's slides had an interesting equation:
a ~ cHo
This is remarkably similar to R = ct, suggesting that they are on to something. (Thanks to nige for pointing out the correct form, which he has pointed out before.) It is good that alternative ideas are being heard.

City of Light Pt. 2

Today at the Invisible Universe, saw talks by George Smoot, Adam Reiss, Ned Wright and others. We ended up having a French banquet at the Pavilion Dauphine. Study of "dark energy" now embraces a variety of ideas. Even Riess admits it might be something other than a cosmic constant. One of these days they may consider a changing speed of light...

City of Light

Am in Paris this week for the "Invisible Universe" international conference. Saturday saw Latin Quarter and Opera House. Today saw Louvre, a reception at the Paris Observatory, and an evening on the Eiffel Tower. Photos soon. In the City light is still slowing.