Question: Recently, I read a book called "Swallowed Star". In the story, a virus changes human DNA enough for humans to have unbelievable superpowers and skills. Some even obtain the ability to have their own gravitational pull and not breathe in space.

I want to know if it is actually possible for genes to be able to cause such things, or is it just impossible theoretically speaking if there isn't enough matter?

PS. Sorry if this sounds like a stupid question. I don't have the knowledge of space and viruses to answer this myself. Please forgive me.

Answer: 
Viruses and pathogens can affect everything that is based on genetic expression or biochemistry: there are known examples of pathogens changing the behavior of their hosts, for example, not forgetting that any pathogen tries to turn its host into a replicator of themselves.

What a virus cannot do is changing the laws of physics.

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> Some even obtain the ability to have their own gravitational pull and not breathe in space
> 
> 
> 

Changing the gravitational pull would require at least one of the three:

1. changing the gravitational constant G
2. changing the mass of the infected
3. changing the distance between the infected and the pulled object

1 is impossible based on what we know today about physics.

2 is trivial, a virus can induce mass weight or mass loss, but the effect is hardly appreciable, unless you want to step in the realm of mama jokes.

3 is also trivial and again hardly appreciable. We get closer or farther to many objects in our daily life, without even realizing that our gravitational pull on them is changing, because it's such a low pull that it can be taken as 0
In real life many people have genes for diseases they will never have. The unlucky ones are the people who get cancer, for example, after suffering a severe infection. The Epstein-Barr virus "turns on" the genes responsible for a certain kind of blood cancer. This is called epi-genetics. It's still a developing field.

In your story, gaining superpowers by way of a virus infection could be explained by an epi-genetic change kicking in, though your human would have to already have the genes necessary to express that power. That can be explained by their ancestors also having had superpowers which would carry through the generations just like hair colour, height, handedness, and a million other characteristics.

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