Expert: Courtney Seligman - 2/27/2010

Question
QUESTION: since it has been proven that motion is relative to time and movement no mater how little actually makes u travel into the future, then lets say i have moved more in my life than my friend so i have infact traveled further into time than him. How come we both still exist in the same moment in time and can communicate and interact etc...

ANSWER: Motion does not cause you to travel into the future. It simply changes how you age, as you do so. If you run around for a year, you will move forward in time by a year, and remain in the same moment of time as your non-moving friend. The only difference is that a clock moving with you would measure a slightly lesser passage of time. Let's say that you move so fast (which would have to be very fast, indeed) that for you, only 11 months passes, while a year passes for your friend. At every moment during his year, you and he would exist in the same moment of time; but your clock would gradually fall behind his, at a rate of one second out of twelve.

In other words, although you would only experience 11 months of time (and aging), you would not move forward in time, relative to your friend. You would always remain in the same moment of time as him. It's just that he would age a little more than you, during that time. So it would be better to say that by moving around, you can remain young for a longer period of time, as perceived by your friend. But the reason isn't because you moved forward in time. It's because you experienced less passage of time, and need another month to "live" as long as he did.

As a different way of looking at it, I often wish that I could put an extra day between now and tomorrow, so that I had more time to do things I would like to do. Unless I could also increase the number of days I have left to live, I wouldn't actually gain any time by doing this. I would simply use up my days at twice the normal rate, and live only half as long, as seen by my contemporaries. In a similar way, as you moved through time, your friend would seem to get older faster than you; but from moment to moment, he would be in the same "moment" as you.

I'm not sure how clear this is. Talking about time, and its different perception in different situations, can be very confusing; and the approach I've used may not properly address the question, as you perceive it. (I always liked Einstein's quote that an hour spent with a pretty girl can seem like a minute, while a minute sitting on a stove can seem like an hour... or words to that effect. But though his words were memorable, whether they properly explained his theory of relativity is another matter.) So if I've misunderstood what you meant, or not made this clear to you, please feel free to restate your question, or to question what I've written.

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QUESTION: also in e=mc^2 it proves that energy and mass are related and by increasing temperature an object actually gains mass. if your reverse this and somehow achieve absolute zero you would say it has no mass and typically you would say an object with no mass is non-existent but yet you could be looking at the object? please just explain in general what happens at absolute zero to objects?

ANSWER: For the simplest case related to your discussion, that of a gas (such as the air in a room), the energy of motion (kinetic energy) would be zero at absolute zero; but there is also a rest-mass, which is independent of motion, and is present even at absolute zero. So objects don't cease to exist if the temperature is equal to absolute zero.

Let's suppose that at absolute zero an object has rest mass RM, and at some temperature T above absolute zero, a kinetic energy equal to 1% of its rest-mass energy RM c^2. Then at that temperature, the effective mass would be 1.01 RM, and the total energy would be 1.01 RM c^2.

Now, let's double the temperature. That would give the object a kinetic energy equal to 2% of its rest-mass energy, an effective mass of 1.02 RM, and a total energy of 1.02 RM c^2.

Finally, drop the temperature to absolute zero, so that the kinetic energy is zero. Then the effective mass would be the rest-mass, or RM, and the total energy would be the rest-mass energy equivalent, or RM c^2. This is not zero, but that doesn't affect the temperature, as that is only related to the kinetic energy, not to the rest mass. And since the kinetic energy is zero, the temperature would be absolute zero.

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QUESTION: (The kinetic energy of an object is the extra energy which it possesses due to its motion.) So when you say air has no kinetic energy wouldnt that be false, because when a gas or air in this example(even though air is a mixture of gases) is in motion we refer to that as wind. And we feel the effects of wind and use it for power. If it had no energy then what would be the point of windmills?

Answer
The movements and physical state of a blob of air can be exploited in various ways. Depending upon the situation, we can divide the energy of the blob into various pieces:

(1) rest-mass energy, which is due to the mass of the blob (the sum of the masses of its individual atoms and molecules). Unless you use the air for some kind of nuclear reaction, this is essentially locked up in the nuclear structure of the atoms, and unavailable (that is, the rest-mass normally remains a constant).

(2) chemical energy, which can be tapped by changing the chemistry of the gas (e.g., if it is methane, combining it with oxygen -- burning it -- to change the structure of the electron shells which surround the atomic nuclei).

(3) kinetic energy of the blob as a whole, due to its overall movement. This is the energy tapped by windmills and such.

(4) heat energy, which is the random energy of the individual atoms and molecules, added together. This is zero at absolute zero, but at higher temperatures, can be utilized by allowing the gas to radiate energy, or by compressing or expanding the gas. For instance, in a heat exchanger, air is compressed, and the work done in compressing it appears as an increase in its temperature (or heat). The hot air can then be used to heat a room. In air conditioners and refrigerators, the heated air is not used to heat a room, but to heat the surrounding regions (usually, the great outdoors). Once the air has radiated its excess heat and cooled off, it is allowed to expand to its original volume, which cools it off by the same amount it was heated by compressing it. Whatever reduction in temperature it experienced while radiating heat in its compressed state is now apparent as a reduction in its temperature compared to its starting temperature, and the cooled air can be used for refrigeration (e.g., air conditioning) purposes. All heat engines and heat pumps use this process, or some variation on it. As an example -- take air in a warm room, at say 80 degrees, and compress it until it is 160 degrees. Pass the hot air through coils, and let it radiate heat until it is only 120 degrees. Now expand the air to its original density and volume, and it will cool by the same 80 degrees it heated up in compressing it, and be only 40 degrees, which is cooler than it started off, and can be used to cool the 80-degree room air. (Actual air conditioners compress and heat the air, then expand and cool it far more; this is just for illustration.)

(5) Potential energy, due to the physical state of the air. Suppose you have warm air filled with water vapor, such as air near the surface of a tropical ocean. Let it rise. As it rises, it expands and cools off. If it cools enough, the water vapor may turn into water droplets, releasing heat referred to as latent energy of condensation. This heat is what drives the vertical motions in tropical thunderstorms -- creating high-velocity winds which may be utilized to create power, or may destroy everything in their path.

There are other ways in which energy stored in the gas can be released, stored, exchanged, or otherwise utilized; but this is probably already a more complicated answer than you wanted or expected.