"In a world without intellectual property laws, what incentivizes entrepreneurs to spend time and money innovating/inventing when someone else can just take their idea after the work is done?" - 
In my opinion, there would still be incentives to invest in innovations and technology, but investors would possibly invest their money differently than they currently do. As Dr. Bylund stated in his lecture, intellectual property laws distort the market because investors choose to invest in products that are easier to protect with a patent. Patent laws also allow the individuals with the monopoly on that specific good or idea to overcharge for their product since there is no availale substitute. Stifling competion usually makes the consumer worse off and it stalls innovation in those products as well.
While there are advantages to intellectual property laws, such as public display of invention designs and reducing people from "stealing" each others ideas, it definitley creates a distortion in the market. Personally, I am not sure if we are better off or not with intellectual property laws, but I tend to lean more towards the advantages of fewer or reduce intellectual property laws. I do not think that getting rid of intellectual property laws would reduce invesment, but I do think investors would be making different investing decisions. If someone can find a more efficient way to produce a good than someone else, than it is for the benefit of society. The premise of being an entreprenuer is to satisfy the needs of a consumer, so the government should not be getting to say who deserves the monopoly on an idea or invention. Also, patents are super expensive, so they help large corporations keep little guys out. I do not think that getting rid of intellectual property laws would have a big effect on the amount investors invest, but I do think it would effect what investors invest in. A possible solution would be to reduce the strength and time of intellectual property laws and see if society becomes better or worse off by this deregualtion and then go from there.