8:1 And when He broke the seventh seal, there was silence in heaven for about half an hour.

And when He broke the seventh seal,

This is the final seal on the scroll. When it is loosened, heaven can begin to see inside and the scroll starts to unfurl. Let's take time here to review the seven seals as they give a hint of the scroll's contents.

The Seven Seals
Seal Number Reference Result
1
 Revelation 6:1 ,2 Atheism
2
 Revelation 6:3 ,4 War
3
 Revelation 6:5 ,6 Famine
4
 Revelation 6:7 ,8 Pestilence & Death
5
 Revelation 6:9 Persecution
6
 Revelation 6:12 Physical disturbances
7
 Revelation 8:1 7 trumpets & 7 vials

there was SILENCE IN HEAVEN for about half an hour.

Silence is NOT a normal state in heaven. When you read the previous chapters (Revelation 4:8), you are struck by all the praising, worshiping, and singing taking place in heaven. To have silence is unusual.

There are two views as to what causes the silence.

It is difficult to say from these views, that any view is the sole cause of the silence. Since God is all knowing (hearing), it seems a little restricting for Him to have silence to hear the prayers Himself. Rather, it may be for the benefit of the angels and saints already present.

As an aside observation, it is typical of the Revelation to have everything explained in precision. That is, the silence is for about half an hour ('not about an hour' or 'some period of time'). This would indicate that what follows with the trumpets is NOT symbolic but EXACTLY what will happen to the earth. The 'thirds' which follow in the rest of this chapter are accurate. If they were symbolic, then they would be 'some' and 'lots' of whatever are burned or destroyed, and the precision of time is not needed in this verse. This is because time is of consequence to earthly things or more precisely, due to the rotation of the earth on its axis; God has no time restrictions!