Lawrence Berkeley National Laboratory 與 High-Z Supernova Search Team 這兩個團體分別發現現今的宇宙膨脹是呈現加速的情形。這個結果出乎許多科學家
的預料；原本他們認為現今宇宙應是處於減速膨脹的時期。因此科學家認為有某種神秘的力量會抵抗重力的吸引力，促使宇宙加速膨脹；這種神秘的力量來源，我們稱呼為為「暗能量」（dark energy）。 科學家提出很多種方案來解釋「暗能量」這種奇特的東西，其中兩個較有名的解釋方案是（1）宇宙常數(Cosmological Constant)及（2）第五元素（Quintessence）。然而這兩種方案依然存在一些問題待解。在這篇論文中，我們探討另一種更自然的模型：dynamical scalar torsion 來解釋「暗能量」的來源。我們發現dynamical scalar torsion 解釋
了現今宇宙呈現加速膨脹的情形，它還告訴我們其實宇宙膨脹的速率是有時加速，有時減速的週期性運動。除此之外，我們的模型還能避免發生在其他模型的一些問題，如巧合性問題、宇宙常數問題等。

Two independent groups, Lawrence Berkeley National Laboratory and the High-Z Supernova Search Team, have observed the presently accelerating expansion of the universe. Their results show that there should be some kind of energy with a negative pressure in our universe called dark energy. This negative pressure can resist the attraction of gravity and make the expansion of the universe accelerate. Some wellknown guesses for dark energy are the cosmological constant and quintessence. All the
proposed models still have many unsolved problems. In this thesis we discuss another
possibility for explaining the accelerating universe: dynamic scalar torsion, which is
based on the Poincar´e gauge theory. The effect of torsion can not only make the expansion rate oscillate, but also force the universe to naturally have an accelerating expansion in some periods and a decelerating expansion at other times. In addition to explaining the accelerating expansion, the effect of torsion could avoid some problems which occur in some other models. In this thesis we include some diagrams to explain
our model and to compare with the data of the Type Ia supernovae.

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