First round decisions are usually made in February. Most departments will
admit a few more students than they actually want (called "over-commits")
with the expectation that some of their admits will choose other schools.
While most departments have an ideal class size in mind at the start of the
admissions process (largely based on expected available funding), large departments
may have more flexibility in regards to the final yield than small departments
(i.e., if the entering class is too small, the department may ask senior students to
TA one semester; if the entering class is too large, a large department is more
likely to have research groups that can come up with additional funding through
an RA). Thus, additional offers of admission may or may not be made later if
a larger than normal percentage of students turn down the offer of admission.
For students on the waitlist, it is important to know that additional offers
may be made at any time during admissions season (Feb - April). However,
most second round (or waitlist) offers will be made in late March/early
April, once the department has a better idea of how many students are likely
to accept (and also once they have a better idea of the actual available funding
for the next academic year).
Once offers of admission have been made, most physics and astronomy departments
encourage (domestic) students to visit during Feb/March/April. Some departments
have official visit days, where you can meet with different research groups,
tour the campus, etc. at the same time as other admitted students. Other
departments organize individual visits - arranged at your mutual convenience.
Reasonable travel costs are usually reimbursed.
By agreement within the Council of Graduate Schools, the official accept/decline
date is April 15 (for US schools). Regardless of when the offer is made, you
cannot be required to respond prior to April 15. However, if you do not
respond by April 15, the offer of financial support may no longer be valid.
Because of this universal response date, students who are waitlisted may
hear that they have been accepted shortly before or after April 15. This
last minute scramble to fill available positions (i.e., to make offers to additional
students) can be minimized if both students and departments act responsibly
and keep in active communication. For students, acting responsibly means
declining offers of admission as soon as you have decided that you will
not attend that school (e-mail is fine). Even if you haven't made a final
decision yet, if you have narrowed your choice down to just 2 or 3, then you
should notify the other schools as soon as possible. This will allow
departments to make timely offers to additional students, which will allow
those students to make timely decisions, which will...etc. It is also
wise to send inquiries to your top choice departments if you have not heard
from them by early April. While rejection letters are not usually sent until
May, you may be able to learn if you are high/low on the waitlist, and whether
they think they will be drawing from their waitlist this year [note, however,
that incessant e-mails, or inquiries starting in early February will be viewed
One final note - when you are accepted, you will likely hear separately from
the department and the graduate school. Unlike undergraduate admissions,
graduate admissions are largely conducted by individual departments. However,
all graduate students are enrolled in the graduate school of the university.
Thus, the department admissions committee reads the applications, decides which
students to admit, and then recommends those students to the graduate school.
The graduate school then looks over the applications, agrees with the
department, and admits those students. Because this process is time consuming,
offers of admission are often written by departments with the phrase "contingent
upon acceptance by the University Graduate School". This is pro forma, and
should not be a cause of concern.