Can you buy rights to airspace in the US? Say I am an astrophysicist setting up a location for an experiment involving measuring electromagnetic field strength from the ground. I can buy loads of land in the Mountain or Midwest regions of the country for my equipment, but I need to be sure I won't have aircraft passing overhead as they'll interfere with the data. Is there a legal channel by which to gain control of the airspace over a patch of property, assuming I'm willing to buy several million acres of land to cover enough area?
A property owner can give you an easement for the air rights of their property, which can allow you to put your own structure over their property or prevent them from putting a structure over their property (depending on the terms of the easement). For instance, a railroad might sell the air rights to an urban rail yard to a private developer so that the developer can put buildings over top of the yard. A high-rise owner might buy an easement for a neighboring property that bans them from building above a certain height in order to keep the views from the high-rise unblocked. However, a property owner can't sell you rights that they themselves don't have. The US government has exclusive sovereignty over US airspace, and there's a public right of transit through navigable airspace (defined as airspace above minimum safe flight altitudes). While the traditional rule was that a property owner owned their land up to infinity, with the development of airplanes this rule has been changed to significantly limit the rights of property owners. The FAA doesn't limit how tall a property owner can build (although too-tall structures can be declared hazards to navigation, which can cause issues with planning boards or insurance companies). However, if there are no obstructions, the airspace above 500 feet in rural areas (in built-up areas it depends on local obstructions) is open for pilots to fly through. The only way to get obstruction-free airspace restricted is to try to get the FAA to issue a flight restriction. If you're trying to get large swaths of airspace restricted, this is extremely unlikely to happen.
When you license your IP (like a song) you can specify the terms and conditions of its use by the licensee, including revenue shares from any derived work. However, if, as your comment suggests, you grant an "informal" license, and later decide that you want to "firm things up" with a license having different terms, that's a matter you would have to either negotiate or litigate with your counterparty. If you want a common reference point for negotiation of this sort of license, you might have a look at compulsory license terms.
Can you prevent the government from using your patent? The opposite is actually true. If you patent something, and it is felt to be potentially of national security interest, then they can take your invention for the nation, produce it, and prevent you producing it or sharing the design indefinitely (though it will be reviewed annually). This has happened to about 5000 patents so far. https://www.wired.com/2013/04/gov-secrecy-orders-on-patents/ Even where it is not of national security interest, and the government (or its contractors!) is not using it directly as covered in user6726' answer, they can still take your patent under the equivalent of eminent domain... well, I'll quote from http://patentplaques-blog.com/eminent-domain-excercised-on-patents/ During World War I, the military took all patents relevant to wireless technology and put them in a mandatory licensing pool. Anyone was then able to use the patents and the patent holders received royalties. The pooling of the patents led to innovations including the mass production of vacuum tubes and a national FM radio network. So, in short, the government can use your invention for its own purposes; it can prevent you from using it; and it can force you to give it to others. They don't do this too often, but if you're working in an area that you think will be of especial interest to them, it's something to be aware of. In general, they will compensate you somewhat for your trouble, but not as much as the open market could have.
The various governments invovled do use eminent domain. An authoritative website about roads, the American Road and Transportation Builders Association says - Between 2000 and 2016, the U.S. built an average of 30,427 lane miles of roadway per year, adding 63.4 square miles per year to the amount of land covered by roads. If all of it needed to be purchased and it was all in Los Angeles (2.7 million per acre) it does, coincidentally come out to 111 billion. Since it will not all be purchased by one entity - every state and the feds make roads and most of the land will be 1/10 of the cost of LA real estate, you will not find anything like that number in a Federal budget.
Generally, if someone asks you to leave their property you have to leave*. Just because a place is owned by the public, doesn't mean anyone can go there any time they wish. Military bases, firehouses, and jails are owned by the public, but many of these have limited access to the public. It may be open to the general public, but that does not mean restrictions cannot be put into place, either on times, or activities, or individuals. For example, public parks often have time and activity restrictions; schools have the power to restrict individuals from their premises, either specifically or by general category. As a general point of law, the owner of any property, or their agent, can order anyone without the right to stay (e.g. not a co-owner or tenant), and that person must depart, otherwise that person is tresspassing. The Social Service Administrator is almost certainly an agent of the controlling entity that owns the property. Thus their demand that you leave the premises is enforceable, unless you have a non-revokable right to be in that space. *As user Justaguy points out there are some exceptions. Most notably, police can some times enter a property uninvited or against the owner's wishes (such as under emergency circumstances or with a warrant).
As the quote in your question notes (albeit in contrapositive form), Asimov's fiction may be made legally available for free download on the net with the permission of his estate. It is either that case that Princeton University's physics department (or whatever individual person or agency put up the story online) has obtained permission from Asimov's estate to distribute the story on their website, or they simply distribute it without legal permission, and Asimov's estate has not taken legal action to have it removed, which they may or may not choose to do in the future. Consider also that the Princeton distribution does not appear to have been meant to be in any way public: looking one directory level up (Princeton University Physics 115A and B: Physics for Future Leaders) shows a course overview with syllabus and lecture notes, without any apparent link to the story. Probably, it was put online for use exclusively by students taking that particular class, and the professor(s) just didn't put any controls to stop it from being accessible to anyone who knew the URL. This doesn't really change that fact that its public accessibility is, strictly speaking, copyright infringement, but it may be a favorable factor toward a finding that distribution outside of the class was innocent infringement, which can lessen (or, rarely, nullify) the penalty. (And it may be quite possible that distribution within the class was defensible under fair use/dealing, which considers educational context as a favorable factor.)
Yes they can You are approaching this from the wrong direction. Their right to enforce what you can and can't do doesn't come from radio-spectrum law; it comes from property and contract law. You are on their property subject to a license that they give you to be there. One of the terms of that license is that you won't set up or operate a wireless network. No doubt there are other things you are not permitted to do; for example, you may not be able to sell goods and services. If you breach the terms of the license then you are trespassing and they are within their rights to have you removed. In addition, if you are a student (or staff), this is probably one of the terms of your contract with the university. If you breach it, they can terminate your candidature (employment). Contracts can impose obligations on you that goes beyond what the law obliges you to do. Indeed, there is no contract if it only requires what is already required.
Can a court order a large asset to be sold if the defendent lost the case on a relatively small amount? Say a defendent owns land worth $200,000. The defendant lost the case and has to pay $9,000. He does not have any money to pay. Could courts order the land to be sold? In most U.S. law jurisdictions, yes, a high value assets can be ordered sold to satisfy a small money judgment or a small secured claim (i.e. a mortgage or the equivalent in real of personal property), subject to some exceptions that don't precisely target this concern but do alleviate it somewhat. Forcing a sale is mostly a decision made by the collection lawyer and the judge has very little discretion in the matter in most cases, so long as all formalities are observed. In most U.S. jurisdictions there are not minimum dollar amount of a debt that can be collected by execution and levy (i.e. seizure and sheriff's sale) on property of arbitrary value (although I am sure there must be at least one out there that does have a minimum dollar amount). Some kinds of property are completely exempt from creditors claims (e.g. defined benefit pension plans). Some kinds of property are protected up to a certain dollar amount of equity (most exemptions for household property and for homesteads, although a small number of homestead exemptions are unlimited). This allows courts and parties to disregard homes with little equity and low value personal property, focusing collection efforts on higher value property. There are also laws in some states require that creditors attempt to collect the debt from all other known assets with equity that can be collected through a formal process (other than a personal residence), before attempting to sell the personal residence (unless the debt is a voluntary mortgage or mechanic's lien on the personal residence and no other assets). There are several ways that the injustice of this can be avoided, if the debtor doesn't simply have the cash to pay off the debt. First, the debtor may be able to borrow the small amount of the debt owed from someone else to pay it off and avoid the foreclosure of the asset. Second, the debtor can take out a loan with the property as collateral to pay the debt, even if the debtor has few other assets. Third, the debtor can sell their own property to pay the debt probably producing a better price than would be obtained at a sheriff's sale. Fourth, someone other than the debtor and the creditor could bid at a sheriff's sale an amount closer to the fair market value of the property than the amount of the debt. Usually, the sheriff's sale price is still far below the fair market value, but it could be a lot more than the debt, and in those cases the excess goes back to the debtor. In some jurisdictions, bids for personal residences must be supported by appraisals that show what the fair market value of the property is and can't be less than that (apart from litigation costs and costs of sale). Fifth, someone could file for bankruptcy and negotiate a payment plan for the small debt in that context.