Just wondered... are people on each level of the academic hierarchy (e.g., lecturer, senior lecturer, professor) considered "equal" with those on the SAME level. For example, a newly appointed professor vs a bunch of more experienced professors, a new PhD vs... etc?

I'm not really into hierarchy by the way. But since it exists, I'm just curious about how it works in academia.

To clarify... I mean for example within a department or research lab.

Clearly not, professors in particular can negotiate their salaries individually with the university.
Apart from that there are hierarchies and structures within the departments with more senior people taking the decisions - they usually have the support of their team. Seniority is influenced by how successful they are in bringing money in. Years in the field also play a role; individuals at professorial level often set up the department.

Hierarchy in PhD students is less clear I would think - I have never been bossed around by a fellow PhD student - but you know what they say, "if you don't know who is the person that everyone hates in the lab then it is probably you". Joking aside, I have been mercilessly attacked by "friends" that I did too much (teaching, marking etc), blocking their development in the group. May they never experience 4th year poverty, and may their data be normally distributed:)

Haha may their data be normally distributed!

Someone got a promotion, is now a prof, and is acting so different all of the sudden, even being a bit arrogant to the other profs - maybe to show that he is one of them now - I don't know. I find it quite interesting to observe!

They are definitely not equal. It goes lecturer - senior lecturer - reader - profs. Everyone bows to the profs, so I'm not surprised you find the new prof throwing his/her weight around!

But I mean are they equal among themselves - like if you become a prof are you then instantly on the same level so as to speak and can throw your weight around with the other profs, or are there sort of sublevels within each level! Slightly complicated and largely pointless question! Just wondering!

I don't think there's real sublevels but I think in reality someone who has been a prof for 20 years is going to have more authority than the newest recruit.