According to the theory of special relativity, an object with mass cannot reach or exceed the speed of light in a vacuum. As an object with mass approaches the speed of light, its relativistic mass increases, requiring an infinite amount of energy to reach or exceed that speed. Therefore, it is not possible for an object with mass to travel at the speed of light.
However, let's consider the hypothetical scenario where an object with massless particles, such as a photon (which is an elementary particle of light), is traveling at the speed of light. In this case, the concepts of time and space undergo significant transformations, and our usual notions of time and experience break down.
From the perspective of a photon traveling at the speed of light, time does not pass for the photon. This phenomenon is known as "time dilation." Time dilation means that for an observer moving at a lower speed relative to the speed of light, time appears to pass more slowly for the object traveling at the speed of light. Conversely, for the object itself, time would not be perceived to pass at all.
Furthermore, as an object's velocity approaches the speed of light, its length in the direction of motion appears to contract. This effect is referred to as "length contraction." For an object traveling at the speed of light, its length would contract to zero.
However, it's important to note that this hypothetical scenario of an object with massless particles traveling at the speed of light is not possible for objects with mass. The theory of special relativity provides insights into the behavior of objects approaching the speed of light, but it does not apply to objects traveling at or beyond that speed.