Listen to part of lecture in an archaeology class.

When we think of large monumental structures built by early societies and Egyptian pyramid probably comes to mind.

But there are some even earlier structures in the British Isles also worth discussing, and besides the well-known circle of massive stones of Stonehenge which don't get me wrong is remarkable enough, well, other impressive Neolithic structures are found there too.

Oh, yes, we are talking about the Neolithic period here, also called the new Stone Age, which was the time before stone tools began to be replaced by tools made of bronze and other metals.

It was about 5,000 years ago, even before the first Egyptian pyramid that some of amazing Neolithic monuments - tombs, were erected at the various sites around Ireland Great Britain and coastal Islands nearby.

I am referring particular to structures that in some cases, look like ordinary natural hills.

But were definitely built by humans, well-organized communities of humans to enclose a chamber or room within stone walls and sometimes with a high, cleverly designed ceiling of overlapping stones.

These structures are called Passage Graves, because the inner chamber, sometime several chambers in fact, could only be entered from the outside through a narrow passageway.

Excuse me, professor, but you said Passage Graves.

Were these just monuments to honor the dead buried there or were they designed to be used somehow by the living?

Ah, yes! Good question, Michael. Besides being built as tombs, some of these Passage Graves were definitely what we might call Astronomical Calendars, with chambers that were flooded with some light on the certain special days of the year, which must've seem miraculous and inspired a good deal of religious wonder.

But research indicates that not just light but also the physics of sound help to enhance this religious experience.

How so?

Well, first the echoes.

When religious leaders started chanting with echoes bouncing off the stone walls over and over again, it must seem like a whole chorus of other voices, spirits of Gods maybe join in.

But even more intriguing is what physicists called Standing Waves.

Basically, the phenomenon of Standing Waves occurs when sound waves of the same frequency reflect off the walls and meet from opposite directions.

So, the volume seems to alternate between very loud and very soft.

You can stand quite near a man singing in a loud voice and hardly hear him.

Yet step a little further way and this voice is almost deafening.

As you move around the chamber, the volume of the sound goes way up and way down, depending on where you are in these standing waves.

And often the acoustics makes it hard to identify where sounds are coming from.

It is as if powerful voices that are speaking to you or chanting from inside your own head.

This had to engender powerful sense of all Neolithic worshipers.

And another bit of physics I played here is something called Resonance.

I am no physicist, but well I imagine you have all blown air over the top of an empty bottle and heard the sound it makes.

And you probably notice that depending on its size, each empty bottle plays one particular musical note.

or as a physicist might put it, each bottle resonates at a particular frequency.

Well, that's true of these chambers too.

If you make a constant noise inside the chamber, maybe by steadily beating drum at a certain rate, a particular frequency of sound will resonate.

We will ring out intensely, depending on the size of chamber.

In some of the large chambers though, these intensified sound may be too deep for us to hear, we can feel it.

We are mysteriously agitated by it, but it is not a sound our ears can hear.

The psychological effects of all these extraordinary sounds can be profound, especially when they seem so disconnected from human doing the drumming or chanting.

And there can be observable physical effects on people too.

In fact, the sounds can cause headaches, feelings of dizziness, increase heart rate, that sort of thing, you see.

Anyway, what was experienced inside one of these Passage Graves clearly could be far more intense than the everyday reality outside, which made them very special places.

But back to your question, Michael, as to whether these graves were designed to be used by the living, well, certainly with regard to astronomical or calendar function,that seems pretty obvious, and I want to go into more detail on that now.