GPS network impacted by time drift

The concept of time continues to amaze and befuddle us.

Here, for example, is one interesting fact: did you know that time travels faster just above the earth than it does on the surface of the planet?

In the 20th century, Albert Einstein had said that time can be understood to flow like a river; in some places it moves faster than others. He also likened it to the fabric of space. Earlier this year, British cosmologist Stephen Hawking provided tantalizing proof of time's fluidity. In a newspaper article, he cited as evidence what happens daily to the Global Positioning System (GPS) satellite network in orbit around the earth. The system that so many of us now rely on for accurate navigation requires the constant adjustment of its computer clocks.

Hawking writes, "Inside each spacecraft is a very precise clock. But despite being so accurate, they all gain around a third of a billionth of a second every day. The system has to correct for the drift, otherwise that tiny difference would upset the whole system, causing every GPS device on Earth to go out by about six miles a day." (Six miles per day!) Imagine what this drift, left unchecked, would do to aviation safety.

Hawking explained that the reason the clocks need adjustment is that the earth's gravity acts like a drag on the flow of time, and actually slows it down compared to the flow of time in space.

For more on Hawking's thoughts about time, including the possibilities of time travel, see Stephen Hawking's Time Machine, which was a summary posted on discovery.com


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Link: Research on the frontiers of physics leads to interesting theories about time travel

To an observer in space, does our planet even exist?

If intelligent life is out there, way out there, would Earth even be visible? The strange answer is "no," but not because we are small or hard to see; but rather because to an observer far away our planet may not exist - yet.

Yes, indeed, another mind-challenging concept from the world of science.

An astrophysicist held an interesting discussion on Canadian radio earlier this year. The topic was the expanding universe, the speed of light and relative distances.

The scientist reminded listeners that when we see light from the stars, we're actually looking back in time. When we look at our nearest star, our sun, we're not seeing how the sun looks now, but how it looked a full eight minutes ago. That's how long it takes light to travel the distance from the sun to the earth.

The really interesting concept relates to other solar systems and galaxies. If we turn the thought around and place ourselves in the role of an observer from far away looking at the earth, then that observer would also be seeing OUR past.

They say the Milky Way, our home galaxy, is about 100,000 light years across. If someone's out there watching us from the other end of our own galaxy, they may be seeing Earth not as it is now, but only as it was when our species, Homo Sapiens, was just distinguishing itself from our "cousins," the Neandertals. No cities, no technology.

And that's just our own galaxy. The universe has millions of galaxies. Any observer watching from any of the other galaxies in our universe would see Earth much earlier in it's history.

So all the observations in space are true only as measurements of the past. Since the size of space is so enormous, even at the relatively fast speed of light, at 300,000 kilometers per second (186,000 miles per second), it takes a relatively long time for light to travel across these vast distances.

Finally, then, if intelligent life were searching for us from 5 billion light years away, they would not see us at all ! To them, we still don't exist. That's because Earth is calculated to be about 4.5 billion years old.

5 billion years ago, our solar system probably was just a loose collection of gases.

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Photo: wpclipart.com

For more thoughts on our universe, see posts in August (Are parallel universes real?)