Even if we don’t know if there is life further away from the Earth, we could arrive to deduct, using the physics laws and the habitat in which they live, which size and form would arrive to have the aliens. For what we know, they wouldn’t be some giant creatures, but they would have a similar size to ours.
What size would they have?
If King Kong really existed, he wouldn’t be able to scare New York city. On the contrary, his legs would break in the moment he started to walk. This phenomenon is due to, if we take a monkey and we multiply its size per 10, then his weight would increase like his volume, that to say, 10 x 10 x 10 = 1000 times. So he would be 1000 times more heavy. But his resistance increases proportionally to the thickness of his bones and muscles. The area of the transversal section of his bones and muscles increases only with the distance square, that to say: 10 x 10 = 100 times. In other words, if a monkey was 10 times bigger, he would only be 100 times more resistant, but he would be 1000 times heavier. Therefore, the weight of the monkey (or of any other animal) enlarges more quickly than his resistance when his size is augmented. He would be, in relative terms, 10 times weaker than a normal monkey, and it is for that reason that his legs would break.
An ant has an enormous strength. She can easily raise a leaf of a much bigger weight than she’s. It can be concluded that if an ant had the size of a house, she could raise it. This hypothesis is incorrect for the same reason that we have just seen with King Kong. If an ant had the size of a house, its legs would break. If we increased the size of the ant in a 1000 factor, then it would bee 1000 times weaker than an ant in normal state.
To one side, in this case of the ant, another problem is present: the ant would suffocate. The ants breathe through holes in the sides of their bodies. The area of these orifices grows as the radium square, but the volume of the ant grows as the radium cube. So, an ant which is 1000 times bigger than an ordinary ant would have 1000 times less air to provide to the muscles and corporal tissues.
From these simple calculations and examples, we could know which approximative size the aliens would have, and it is for that reason that we know that they wouldn’t be some giant beings, but they would be, in size, similar to us.
Can we know an approximative form?
Using this scale scale law, we can also calculate the approximate form of the animals on the Earth, and possibly of the aliens in the space.
The heat which is emitted from an animal increases when its superficial area is increased. For this reason, when its lineal size is augmented in a 10 factor, its thermic wastes increase in 10 x 10 = 100. But the contents of heat in its body is proportional to its volume, or 10 x 10 x 10 = 1000. As more small is an animal, more augments its relative surface, which makes to increase the area in which its heat escapes, and for consequence the small animals need a bigger heat production for unit of weight. Because of this, the big animals lose warmth more slowly than the smaller animals.
This is the reason for which our fingers and ears freeze the first, as they have a bigger relative surface. It is also the cause that the smaller persons freeze more quickly than the bigger ones. It also explains why the newspapers burn very quickly, due to their bigger relative surface, while the logs burn more slowly, as they have a relatively small surface.
This phenomenon explains why the whales in the Arctic have a circular surface: because a sphere has the minimum surface per mass unity. It also explains why the insects in a hot ambient have a thorn form, which makes to have a relatively big surface per unit of mass.
In an analogous way we can do an approximative estimation of the surface and volume of the animals in far planets using the physics laws. From this laws we can theorize that the aliens in the exterior space wouldn’t probably be the giants that are often represented in the science-fiction, but closer to us in size. The size and form of the aliens wouldn’t be too different to ours.
However, the habitat in which they leave must be considered. The whales, for example, can have a much bigger size due to the force of the sea water. This explains why the whales die when they stuck in the beaches, as they are squashed by their own weight.