Apophis: The Asteroid That Could Smash Into The Earth on Friday, April 13th, 2036

Apophis is an asteroid with an slightly offset orbit to that of Earth's. Discovered in June 2004, astronomers have determined that it will make a very close flyby on April 13th, 2029, where it will pass to within 5 Earth diameters of us. The exact path the asteroid follows on its flyby in 2029 will determine whether it smashes into the Earth seven years later.

Earth impact animation (8 sec)
Credit: ESA/Hubble
(M. Kornmesser & L. L. Christensen)

In 2004, it was first thought that the asteroid would hit us in the first flyby in 2029. The initial calculation for the orbit was made using only two sets of observations, those made in June and a subsequent set made in December.

From those observations, astronomers calculated a 1-in-200 chance that the asteroid would hit the Earth. If this was true, then this asteroid had become the most dangerous asteroid ever found. After taking more observations , the chances climbed even higher and by the end of December 2004, the chances of the Earth being struck by this asteroid climbed as high as 1-in-37.

Normally, when more observations are taken the chances of this kind of collision decrease. Not so here, it seemed like this thing was really going to hit us.

Luckily, some other observations from other sources were located and they allowed astronomers to calculate a more precise orbit. From those images they were able to conclude that there was no way that Apophis was going to hit the Earth. Whew!

How could a mosquito fly in mid air in a moving bus?

assume that the bus is already driving at constant speed, no
acceleration or deceleration.
The reason why a mosquito can fly inside a moving bus is, that you have a closed
system. Everything in this bus is moving at the same speed including the air,
every single molecule. This means all air molecules move with the same speed as
the bus. So a mosquito flying inside the bus only has to deal with movements
relative to the surrounding air inside the bus.

During acceleration or deceleration this is much more difficult. The mosquito
probably would not be able to stay on its course - similarly to a passenger in a
train, who tries to stand still while the train starts moving or while it is
stopping.

Also things change dramatically if the bus becomes an open system. Take out the
front windshield and your mosquito will not fly anymore.

By the way, we also can see our earth as the bus we are all sitting in. Earth has
a distance from the sun of about 150 million kilometers and moves around the sun
within one year. To do so the earth must have an average speed of more than
100000 kilometers per hour (76000 miles per hour). Still we can walk, drive, sit
.... because we experience our earth as closed reference system.

Is Time is Slowing down?

Time may literally be running out – and could one day vanish altogether, according to a bizarre new theory. The suggestion has been put forward to explain a cosmological mystery that has baffled scientists. A decade ago, measurements of the light from distant exploding stars showed the universe to be expanding at an accelerating rate. Physicists assumed that a kind of anti-gravitational force must be driving the galaxies apart, and gave it the name “dark energy”. However, to this day no-one has been able to say what dark energy is or where it comes from. The new theory from Professor Jose Senovilla, at the University of the Basque Country in Bilbao, Spain, offers a radical alternative idea. He believes there is no such thing as dark energy. Instead, he says we have been fooled into thinking the expansion of the universe is accelerating because time itself is slowing down.At our local everyday level, the change would be imperceptible.

But it would be obvious from cosmic scale measurements tracking the course of the universe over billions of years. Astronomers work out the speed of the universe’s expansion from the frequency of light emitted by certain types of supernovae, or exploding stars. However, these measurements depend on our current perception of time, says Prof Senovilla.If time has been slowing down, and clocks are now running more slowly than they did long ago, it would appear from our perspective as if things have been speeding up. Looking back over billions of years, galaxies would seem to be travelling away from each other faster and faster at various intervals since the Big Bang.

“Our calculations show that we would think that the expansion of the universe is accelerating,” said Senovilla.His idea is based on string theory concepts which allow dimensions of space and time to switch from one to another.
If our single time dimension was changing into a new space dimension, it would produce just such an effect.After billions of years, time would eventually disappear altogether.“Then everything will be frozen, like a snapshot of one instant, forever,” Prof Senovilla told New Scientist magazine. “Our planet will be long gone by then.”Prof Gary Gibbons, a cosmologist at Cambridge University, is drawn to the idea. “We believe that time emerged during the Big Bang, and if time can emerge, it can also disappear – that’s just the reverse effect,” he said.