If the parliament passes something that you don't want, you can collect 50'000 signatures and challenges the decision. If you managed to collect these signatures, then the law will voted by the whole population in the next votation (we have like 3-4 votations per year).

On the other hand, if you want to propose a law, you can collect 100'000 signatures and create an "initiative". After evaluation of the feasibility of this law, it will be the subject of a nation-wide votation.

Its the other way around, 100k for an initiative, 50k for a referendum.

My bad, I confused the numbers. I corrected

How does the evaluation of the feasibility of the proposed law work?

Well, generally if you propose a law like that there is a large discussion around it and those that propose it usually write a whole bunch of 'this is why its a good idea' stuff.

The Bundesrat (i.e. the State Council) sometimes proposes an alternative. So they might say 'Initiative X proposes Y, but the State Council recommends a compromise where we do Z instead'. And then when you vote on it you have 3 options, rather then just 'yes' or 'no'.

There is also a check of the highest court, where they basically say 'this isn't really according to international law'. However that is just a recommendation and people can ignore it when voting.

Also, even if something goes threw, the actual implementation usually slightly adjust to reality on the ground somewhat.

That's how Swiss politics work. If you can get 100000 voters to sign a petition it triggers a referendum. And that's basically how any opposition to such a project is expected to proceed.

50k. 100k is for if you want to introduce a new law.

Here’s the official information provided by the Swiss authorities related to political rights of referendums, petitions, and right to vote, which is a filter for participation:

https://www.ch.ch/en/political-system/political-rights/

Not sure exactly what you're asking, and also not from Switzerland, but what I can comment on is the fact that IIRC correctly, it is fairly easy to launch a "referendum" in Switzerland, i.e. something (a new law, or the overturning of one, or a project like this being canned) to be submitted to a direct vote from the entire population.

correction: It's a referendum (oppose a law enacted by the parliament), so you need to collect 50 000 signatures. For a petition (changing the consitituion) you need 100 000. However, the vote in the parliament was quite clear. For example, in the Ständerat 43:0, so it would have been a surprise if a referendum were launched. Swiss politics is not consensus-based. However, you don't have just two parties that oppose each other. As most parties somehow play part in the government (some more, some less), destructive behavior is frowned upon unlike in other countries. That's why maybe some think it's consensus-based. Furthermore, due to the strong federal system and general culture, minorities need to be considered. Moreover, Switzerland is a small country, which makes some behavior difficult (see also destructive behavior above).