Suppose we have a planet whose atmosphere has roughly the same gaseous proportions as Earth, but helium replaces nitrogen, and has a strong hydrogen presence in the upper atmosphere; has a gravitational pull stronger than Earth; and has a thicker atmosphere than Earth (from the planet's surface to the boundary with space). What effect would these conditions have on the development of science and technology from a human perspective? Fields I am interested in seeing an impact to include, but are not limited to, the following:
- Flight. Lighter-than-air vehicles would likely require heated helium or hydrogen to maintain flight, but what about fixed- and rotor-wing craft? Would it be easier or harder to fly, or would there not be a noticeable difference?
- Communication. Waves propagate through different materials/densities at different rates. Would there be a noticeable effect on the transmission of, e.g., radio waves?
- Diving. When scuba divers make deep dives, they swap out the nitrogen in their compressed air tanks for helium (this was the idea behind the atmospheric change). Would helium still be a viable option for deep dives?
- Explosives. As with communication, waves have varying propagation factors. Would explosions be noticeably affected? For example, would they be more destructive, but in a smaller radius?
- Firearms. In extension to explosives, would firearms be noticeably affected? Gravity would be likely to pull ammunition to the ground faster. Would projectiles face more or less resistance from the altered atmosphere, potentially affecting the effective range?
- Spaceflight. Modern rocketry is built on the concept of a controlled explosion. Which factor would play the greatest role in deterring/encouraging spaceflight: the helium in the atmosphere, the strong gravity well, or the height of the atmosphere? Also, would modern rocket engines cause the high hydrogen content in the upper atmosphere to explode, effectively preventing such vehicles from reaching space?
Please note: I am not altogether interested in an exploration of the impact of these changes on the human physiology; humans would probably be shorter, denser, and sound like Alvin and the Chipmunks.
If there are any areas I have not already listed you believe would be noticeably affected by the conditions described above, feel free to list them.
Addendum: I've noticed a lot of the answers tend to be about the feasibility of life developing in a helium-based atmosphere rather than the impact the atmosphere would have on the development of scientific understanding. Just to be clear, this planet is not Earth, so any biological factors can be assumed to be properly developed for the indicated atmosphere. Answers to this question should only be about the impact on various fields of science and technology.