Perpetual Motion and the Laws of Thermodynamics

[binbots]

How come we say perpetual motion is not possible according to the laws of thermodynamics. Yet our universe is expanding faster and faster. How can we say nothing is faster than the speed on light but the universe expanding is? Keep it simple please.

 

[Galap]

The universe is not expanding faster than C. if it were, light from distant galaxies would never reach us because the space between them would grow faster than the light could cross it.

As for perpetual motion, It is not the same as a force. We do not know why the universe is expanding faster and faster, but it seems to be due to some accumulating acceleration. We do not say an orbiting satellite is perpetual motion, yet it perpetually moves. Be careful with the definitions.

 

[LostConjugate]

I think what bin is asking is that if it is expanding at any rate, wouldn't it eventually exceed the speed of light far enough away. The answer is no, relative to any observer in the universe nothing is moving faster than the speed of light.

Speed is distance over time, but take the time of any relative object and you get

$$t' = \frac{t}{1-\frac{v^2}{c^2}}$$

So

$$\frac{d}{t'}$$

will never exceed c where c is the speed of light.

 

[AUK 1138]

Back in one of my astro classes my professor tried to explain that what's happening is that the objects aren't 'moving' away faster than the speed of light, but instead, the distance between the objects is getting longer! kind of like drawing two dots on a balloon and filling it up, they aren't moving with respect to the balloon, but are becoming farther apart due to its expanding nature. now, obviously this balloon example is wholly crude, but the point is that it's not that the objects are moving, but instead, the way we perceive distances have changed and are changing with respect to time. i hope this helps.

 

[pmacias]

Perpetual motion is the concept of a machine that can continue to operate indefinitely without the need for external energy input. This idea has been pursued by many inventors and scientists throughout history, but it has always been proven impossible according to the laws of thermodynamics.

The laws of thermodynamics state that energy cannot be created or destroyed, only converted from one form to another. In other words, the total amount of energy in a closed system remains constant. This means that any machine or system that claims to produce unlimited energy without any input is violating the first law of thermodynamics.

Additionally, the second law of thermodynamics states that in any energy transfer or transformation, some energy will inevitably be lost as heat. This means that the efficiency of any machine or system will always be less than 100%, and therefore it cannot continue to operate indefinitely without an external energy source.

As for the expansion of the universe, this is not a violation of the laws of thermodynamics. The universe is not a closed system, as it is constantly interacting with and receiving energy from outside sources. The expansion of the universe is driven by the force of dark energy, which is a mysterious form of energy that pervades all of space. This does not contradict the laws of thermodynamics, as the energy for the expansion is coming from outside the universe.

Furthermore, the speed of the expansion of the universe is not comparable to the speed of light. The expansion of the universe is happening at a rate relative to the scale of the universe, not at a speed through space. Therefore, it is not violating the principle that nothing can travel faster than the speed of light.

In conclusion, perpetual motion is not possible according to the laws of thermodynamics because it would violate the conservation of energy and the inevitability of energy loss. The expansion of the universe, while seemingly fast, is not a violation of these laws as the universe is not a closed system.