Learn Hardcore German: Unsere Zugtickets sind schon vor zwei Wochen online gebucht worden. - Our train tickets were already booked online two weeks ago.

Vorgangspassiv (event passive), Perfekt:
- Unsere Zugtickets sind schon vor zwei Wochen online gebucht worden.
- Auxiliary sein (in the present) + past participle (gebucht) + worden
Vorgangspassiv, Präteritum (simple past):
- Unsere Zugtickets wurden schon vor zwei Wochen online gebucht.
- Simple past of werden (wurden) + past participle (gebucht)

Both sentences are grammatically correct and mean the same thing in most contexts: Our train tickets were already booked online two weeks ago.

Style difference:

Perfekt (sind … gebucht worden) is more typical in spoken German (especially in southern regions).
Präteritum (wurden … gebucht) is common in written German and in the north.

So the sentence uses sind … gebucht worden simply as the Perfekt passive form.

Why is it worden and not geworden?

German has two different forms related to werden:

worden
- Used in the Vorgangspassiv in compound tenses (Perfekt, Plusquamperfekt, Futur II):
  - Die Tickets sind gebucht worden. – The tickets have been booked.
- It does not mean "become" here. It’s just the special passive auxiliary form.
geworden
- Past participle of werden in its meaning to become:
  - Er ist müde geworden. – He has become tired.

Rule of thumb:

Passive + past = worden
“Become” + past = geworden

Why is the auxiliary sein used here, not haben?

In the event passive (Vorgangspassiv), German always uses werden as the main passive auxiliary, and in compound tenses its auxiliary is sein:

Present passive:
Die Tickets werden online gebucht.
Perfect passive:
Die Tickets sind online gebucht worden.

Structure in the perfect passive:

Auxiliary of werden in Perfekt → sein
Past participle of the main verb → gebucht
Special passive form → worden

So:

sind (Perfekt of sein, 3rd person plural)
gebucht (past participle)
worden (passive marker)

You never use haben for the Vorgangspassiv.

What is the difference between sind gebucht and sind gebucht worden?

They are two different types of passive:

sind gebucht worden – Vorgangspassiv (event passive)
- Focus: the action of booking took place.
- Unsere Zugtickets sind schon vor zwei Wochen online gebucht worden.
  → The act of booking happened two weeks ago.
sind gebucht – Zustandspassiv (state passive)
- Focus: the resulting state after the action.
- Unsere Zugtickets sind (schon) gebucht.
  → Our tickets are (already) booked. (They are in the “booked” state now.)

So:

Use sind gebucht worden when you care about when / how the booking happened.
Use sind gebucht when you care about the current state (they’re booked, not free).

Why is it unsere Zugtickets and not something like unseren Zugtickets?

Zugtickets is:

plural
neuter in singular (das Zugticket, plural die Zugtickets)

In the sentence:

Unsere Zugtickets is the subject of the passive verb (sind gebucht worden).
The subject is in the nominative case.
For unser- in the nominative plural, the ending is -e: unsere.

Case pattern for unser- (relevant parts):

Nominative plural: unsere Tickets
Accusative plural: unsere Tickets (same form)
Dative plural: unseren Tickets

So unsere Zugtickets is nominative plural and correct as the subject.

Why is unsere Zugtickets the subject in the passive, when it would be an object in English?

In active voice, the logical structure would be:

Jemand hat unsere Zugtickets schon vor zwei Wochen online gebucht.
- jemand = subject (nominative)
- unsere Zugtickets = direct object (accusative)

In passive, German (like English) makes the object of the active sentence into the subject:

Unsere Zugtickets sind schon vor zwei Wochen online gebucht worden.
- unsere Zugtickets now functions as subject (nominative).

English does the same:

Active: Someone booked our tickets two weeks ago.
Passive: Our tickets were booked two weeks ago.

So the German structure matches English: the former object becomes the new subject in the passive.

What is the infinitive of gebucht, and how is this participle formed?

Infinitive: buchen (to book, to reserve)
gebucht is the Partizip II (past participle).

For regular (weak) verbs like buchen, the participle pattern is:

ge-
- verb stem + -t

So:

buch- (stem) → ge-buch-t = gebucht

This participle is used:

in the active perfect:
Wir haben die Tickets online gebucht.
in the passive:
Die Tickets sind online gebucht worden.

What does schon add here, and where can it go in the sentence?

Meaning:

schon here means already.
It indicates that the action happened earlier than someone might expect.

Nuance:

Without schon: Unsere Zugtickets sind vor zwei Wochen online gebucht worden.
→ Neutral: just states the time.
With schon: Unsere Zugtickets sind schon vor zwei Wochen online gebucht worden.
→ Suggests: “(Surprisingly / as you can see) it was already two weeks ago.”

Position:

The given position is very natural:
- … sind schon vor zwei Wochen online gebucht worden.

Other positions are possible but less neutral:

Unsere Zugtickets sind vor zwei Wochen schon online gebucht worden. (slightly different emphasis)
Unsere Zugtickets sind online schon vor zwei Wochen gebucht worden. (stronger focus on online already)

Standard, most natural version is exactly as in the sentence: schon vor zwei Wochen online.

Why is it vor zwei Wochen and not seit zwei Wochen?

Both vor and seit talk about time, but they are used differently:

vor
- time expression = a point in the past, completed
- vor zwei Wochen = two weeks ago
- Used with events that are finished:
  Unsere Zugtickets sind vor zwei Wochen gebucht worden.
seit
- time expression = since / for and the situation continues until now
- seit zwei Wochen = for two weeks / since two weeks ago
- Used with ongoing states or actions:
  - Wir haben die Tickets seit zwei Wochen. – We’ve had the tickets for two weeks.
  - Seit zwei Wochen warten wir. – We have been waiting for two weeks.

The booking event happened at a specific point in the past, so vor zwei Wochen is correct.

What is online grammatically, and where can it appear in the word order?

online in German is:

an adverb (also used like an invariable adjective in some contexts)
it does not change its form (no gender, number, case endings).

In this sentence, it modifies gebucht (how/where the tickets were booked).

Typical adverb order rule (simplified TMP):

Time – Manner – Place (though online is a kind of "manner/location in the internet").

Possible positions:

Unsere Zugtickets sind schon vor zwei Wochen online gebucht worden. (very natural)
Unsere Zugtickets sind schon vor zwei Wochen gebucht worden, online. (possible, but sounds a bit tacked-on)
Unsere Zugtickets sind online schon vor zwei Wochen gebucht worden. (emphasis on “online”)

The original position (just before gebucht) is the most neutral and idiomatic.

How would this sentence look in the active voice?

A natural active version would be:

Jemand hat unsere Zugtickets schon vor zwei Wochen online gebucht.

or, more generally:

Man hat unsere Zugtickets schon vor zwei Wochen online gebucht.

Structure:

Jemand / Man = subject (doer of the action)
hat gebucht = active perfect
unsere Zugtickets = direct object
schon vor zwei Wochen online = adverbials

The passive version hides the agent:

Unsere Zugtickets sind schon vor zwei Wochen online gebucht worden.
→ We focus on the fact that the tickets are booked, not on who did it.

Could I say Unsere Zugtickets wurden schon vor zwei Wochen online gebucht instead? Is there any difference?

Yes, you can, and it is perfectly correct:

Unsere Zugtickets wurden schon vor zwei Wochen online gebucht.

Difference:

wurden gebucht = Präteritum passive
sind gebucht worden = Perfekt passive

In meaning, they are practically the same here.

Usage tendencies:

wurden gebucht is very common in written German (reports, news, formal texts).
sind gebucht worden is more common in spoken German, especially in southern regions.

So it’s mostly a stylistic/region preference, not a meaning difference in this context.